Patent Grant
10466245
The invention relates to the field of biological indicators, and in particular to biological indicators for the validation of treatment processes designed to reduce the amount or activity of a contaminant in a sample. The invention further relates to methods of preparing these indicators, and to the uses thereof.
A wide variety of biological indicators are known for validating cleaning and decontamination processes. These range from relatively basic indicators, such as those that use a simple “visual score” to assess whether a process has been effective, to more sophisticated indicators that rely on thermostable kinases as reporter enzymes (WO2005/093085). These kinase-based indicators have been an important development in the biological indicator field, providing a rapid and sensitive means of process validation.
WO2005/093085 describes in detail the production and use of the kinase-based indicators referred to above. In summary, a typical indicator is prepared by adsorbing a thermostable kinase onto a solid support such as an indicator strip or dipstick. The indicator is then included with a sample (containing a contaminant) to be treated, and the indicator plus sample are subjected to a treatment process. The reduction in activity of the indicator kinase by the treatment is then correlated with the reduction in amount or activity of the contaminant. When a level of activity is determined that is known to correlate with an acceptable reduction in the contaminant, the treatment is then regarded as validated.
It has now been found that the performance of these kinase-based indicators can be significantly improved by covalently cross-linking the thermostable kinase to a biological component, wherein the biological component is a mimetic/surrogate of the contaminant. This allows the indicator to more accurately reflect the reaction of the contaminant to the treatment process, which in turn leads to improved indicator accuracy/sensitivity, and thus fewer “false” process validations.
Advantageously, the biological component may be part of a biological matrix or mixture, such as a commercially available test soil (Browne soil, Edinburgh soil etc.), blood, neurological tissue, food, culled animal material, serum, egg, mucus, or a test soil made up to meet the specific requirements of the user. In this way, the reduction in the amount/activity of the kinase is a function of the diverse properties of the matrix, which further improves the accuracy/sensitivity of the indicator.
An indicator of this type is also able to monitor the removal/inactivation of a specific component of the matrix or mixture. Advantageously, an indicator can be designed so that the thermostable kinase is linked to the most “difficult” component of the matrix to remove/inactivate (e.g., in a matrix of blood, fibrin is much more difficult to remove than haemoglobin). This provides for an extremely stringent validation of the treatment process.
The indicators described above also have the advantage of providing rapid, single step, process validations. This is in contrast to certain known validation indicators, which require multiple steps for validation and therefore require a much greater investment of time and effort. By way of example, WO00/65344, describes the use of a yeast prion as a biological indicator for a prion decontamination process. At the end of the process, the operator must, in a further step, assay the destruction of the yeast prion in order to validate the process. In contrast, the indicators described above are designed to have an indicator kinase linked directly to a biological component that mimics the relevant contaminant (e.g., prion) so that the destruction of this component is intimately linked to the loss of kinase activity. As such, these indicators are able to provide for a rapid single-step indication of process efficacy.
The invention therefore addresses the problem of providing an alternative/improved kinase-based biological indicator.
Biological Process Indicator
In a first aspect of the invention, there is provided a biological process indicator for validating a treatment process in which the amount or activity of a contaminant in a sample is reduced, wherein the indicator comprises a thermostable kinase covalently linked to a biological component, with the proviso that the biological component is not an antibody.
In one embodiment, the biological component is a mimetic or surrogate of the contaminant, and therefore reacts to the treatment process in substantially the same way as the contaminant. In another embodiment, the biological component may be the same as, but physically distinct from, the contaminant in the sample that is to be subjected to the treatment process, e.g., if the contaminant is a protein, then the biological component is also a protein; if the contaminant is a blood protein, the biological component is also blood protein; if the contaminant is a DNA molecule, then the biological component is also a DNA molecule; if the contaminant is an RNA molecule then the biological component is also an RNA molecule, etc. for each of the contaminants and biological components disclosed in this specification. In a further embodiment, the biological component may be different from the contaminant.
Examples of biological components that can be used in the indicators of the invention include proteins, nucleic acids, carbohydrates and lipids.
In one embodiment, the biological component comprises a protein selected from the group consisting of a blood protein, a bacterial protein, a viral protein, a fungal protein, and a self-aggregating or amyloid forming protein.
In a further embodiment, the blood protein is selected from the group consisting of blood clotting proteins (e.g., fibrinogen, fibrin peptides, fibrin, transglutaminase substrates, thrombin), serum proteins (e.g., albumin and globulin), platelet proteins, blood cell glycoproteins, and haemoglobin.
In another embodiment, the bacterial protein is selected from the group consisting of a bacterial fimbrial protein (e.g CgsA from E. coli and AgfA from Salmonella), a bacterial toxin protein (e.g., toxins from Bacillus anthracis, Corynebacterium diphtheriae, Clostridium botulium), a bacterial cell surface protein (e.g., peptidoglycan, lipoproteins), and a bacterial spore protein (e.g., from Gram positive bacteria and having a similar sequence or overall structure to the proteins forming ribbon appendages in Clostridum taeniosporum, chaplin proteins, rodlin proteins).
In yet another embodiment, the viral protein is selected from the group consisting of a viral envelope protein, a viral capsid protein, and a viral core protein. Suitably, the viral proteins are from a bacteriophage virus (e.g., the MS2 and PP7 proteins), norwalk virus (e.g., capsid protein), rotavirus (e.g., VP2, VP6 and VP7 proteins), coronavirus (e.g., SARS S, E and M proteins), bluetongue virus (e.g., VP2 protein), human papillomavirus (e.g., viral major structural protein, L1), hepatitis B (e.g., small envelope protein HBsAg), Hepatitis C virus (e.g., core, E1 and E2 proteins), influenza virus (e.g., neuraminidase and haemagglutinin and matrix proteins), poliovirus (e.g., capsid VP0, 1 and 3 proteins), HIV (e.g., Pr55gag, envelope proteins) and dengue B virus (e.g., envelope (e) and pre-membrane/membrane (prM/M).
In another embodiment, the fungal protein is selected from the group consisting of hydrophobin proteins (e.g., SC3 from Schizophyllum commune, RodA/B from Aspergillus fumigates, and equivalent proteins from yeast), fungal spore proteins, hyphal proteins, mycotoxins, and fungal prions (e.g., Sup35, Het S, URE 2, Rnq1, New 1).
In yet another embodiment, the self-aggregating protein is selected from the group consisting of prions (e.g., PrPSc and PrPc, Sup35, Het S, Ure 2, Rnq1, New 1), prion mimetic proteins, amyloid fibrils, cell surface adhesins from floc forming and filamentous bacteria in activated sludge, beta amyloid protein, tau protein, polyadenine binding protein, herpes simplex virus glycoprotein B, lung surfactant protein C, CsgA protein from E. coli, AgfA protein from Salmonella species, bacterial fimbrial proteins, apolipoproteins (e.g., apolipoprotein A1), hydrophobins from fungal species (e.g., SC3 from Schizophyllum commune, RodA/B from Aspergillus fumigates), chaplins (e.g., Chps A-H from Streptomyces spp), rodlins (e.g., Rd1A and Rd1B from streptomyces spp), gram positive spore coat proteins (e.g., P29a, P29b, GP85 and a SpoVM analogue), and barnacle cement-like proteins (e.g., the 19 kDa protein from Balanus albicostatus, and the 20 kDa protein from Megabalanus rosa, and the novel calcite-dependent cement-like protein from Balanus albicostatus).
In another embodiment, the nucleic acid is selected from a DNA molecule and an RNA molecule. In a further embodiment, the nucleic acid is selected from single-stranded DNA (ssDNA), single-stranded RNA (ssRNA), double-stranded DNA (dsDNA) or double-stranded RNA (dsRNA). In one embodiment, the nucleic acid is derived from neurological tissue.
In another embodiment, the carbohydrate is selected from the group consisting of exopolysaccharide, lipopolysaccharide (EPS/LPS, sometimes known as endotoxin) (e.g., from Legionella species, E. coli, Staphylococcus species, Streptococcus species, Pseudomonas species, Acinetobactor species, Campylobactor species, and Bacillus species), peptidoglycan, cell wall components of plants, fungi and yeast (e.g., chitin, lignin, glucan), mucin preparations, glycolipids (especially brain derived glycolipids), glycoproteins (e.g., cell surface glycoproteins, Eap1p), spore extracts (e.g., from Bacillus spp, Clostridal spp and other spore-formers), polysaccharides from yeast capsules, and invertebrate secretions (e.g., from molluscan gels).
In another embodiment, the lipid is selected from the group consisting of glycolipids (e.g., brain-derived glycolipids), gangliosides (e.g., neuronal cell gangliosides such as GT1b, GT1a and gangliosides of more general cell origin such as GM1), and plant oils and lipids.
In a further embodiment, the biological component is part of a biological matrix. In one embodiment, the indicator is covalently linked to the biological matrix. The biological matrix may be a mimetic of the sample that is to be treated. In one embodiment, the biological matrix comprises one or more components selected from the group consisting of proteins, lipids, nucleic acids, and carbohydrates, or fragments or derivatives thereof. In another embodiment, the biological matrix may comprise a mixture of proteins. In a further embodiment, the biological matrix may comprise one or more components selected from the group consisting of blood, serum, albumin, mucus, egg, neurological tissue, food, culled animal material, and a commercially available test soil. In yet another embodiment of the invention, the biological matrix comprises one or more components selected from the group consisting of fibrinogen, thrombin, factor VIII, CaCl2, and, optionally, albumin and/or haemoglobin.
In one embodiment of the invention, the thermostable kinase is covalently linked to the biological component. In another embodiment, the thermostable kinase is genetically or chemically cross-linked to the biological component. In a further embodiment, the biological component is linked to the thermostable kinase in the form of a fusion protein.
The indicators of the invention may be used to validate treatment processes designed to remove/inactivate a contaminant selected from the group consisting of a protein, a lipid, a carbohydrate and a nucleic acid.
The biological process indicator of the invention may further comprise an agent to stabilise the kinase, such as metal ions, sugars, sugar alcohols or gel-forming agents.
The indicator of the invention (including any biological matrix) may also be “fixed” by treatment with 70% ethanol or isopropanol. To achieve this, the indicator/matrix is incubated in 70% isopropanol for 30 minutes at room temperature. This mimics one of the commonly encountered processes which may increase the resistance of contaminating materials on surgical instruments, and therefore provides the indicator with an effective way of monitoring the removal of such materials.
The biological process indicator of the invention may be immobilised in or immobilised on a solid support. In one embodiment, the biological process indicator is immobilised in the solid support, or is immobilised on the solid support by chemical cross-linking or adsorption. The indicator may be attached to the solid support via the thermostable kinase, or via the biological component.
In one embodiment, the solid support is an indicator strip, a dip-stick or a bead, and, optionally, further comprises means to attach the solid support to a surface (such as a projection, recess or aperture for attachment of the solid support to a surface by means of a screw, nut and bolt, or clamp). In a further embodiment, the solid support is a matrix and the indicator is dispersed within the matrix.
In one embodiment of the invention, the enzyme used to form the biological process indicator is not a lichenase, a xylanase, a xylosidase, a formiltransferase, a Taq polymerase, an alpha-amylase, or a beta-glucosidase.
In yet another embodiment of the invention, there is provided a test soil comprising an indicator as described above.
Preparation of the Biological Indicator
The biological indicator of the invention may be prepared by covalently linking a thermostable kinase to an appropriate biological component. Any suitable method of covalent attachment known in the art may be used. In one embodiment, the thermostable kinase is genetically or chemically cross-linked to the biological component, and in one embodiment, the indicator is prepared as a fusion protein.
Chemical cross-linking may be achieved using a range of homo- and hetero-bifunctional reagents commonly used for cross-linking of proteins for the generation of enzyme conjugates or other related purposes. For example, in an indicator comprising fibrin as the biological component, the fibrin and the thermostable kinase may be derivatised with the addition of SPDP (Perbio) to primary amine groups. The thermostable kinase can then be reduced to generate a reactive thiol group and this is then mixed with the fibrin to produce covalent fibrin-thermostable kinase linkages.
The kinases can also be chemically cross-linked to carbohydrates, lipids or other glycoconjugates using heterobifunctional agents following treatment of the target carbohydrate with meta-periodate. The cross-linking may be achieved using a variety of chemistries as outlined in Example 23.
Alternatively, the indicator may be prepared as a fusion protein. This is achieved by fusing a synthetic gene encoding an appropriate thermostable kinase (e.g., the gene encoding AK from Sulfolobus acidocaldarius or Thermatoga neopolitana) to a gene encoding an appropriate biological component. Detailed protocols for the preparation of fusion protein indicators are given in the Examples (see e.g., Examples 10 & 13).
Kinase Enzymes for Use in the Biological Indicator
The kinase enzymes used in the indicators of the invention are capable of generating a signal that is detectable over an extremely wide range. Generally, the kinase is detected using a substrate comprising ADP which is converted to ATP, itself used to generate light, eg. using luciferin/luciferase, detected using a luminometer. The wide range makes the indicator particularly suitable for validation as the kinase remains detectable even after many logs reduction in amount/activity. For sterility, most national institutes regard a 6 log reduction in the amount or activity of a contaminant as required before sterility can be validated. The kinases used in the indicators of the invention offer the potential of validating reduction in the amount or activity of contaminants well beyond 6 logs, to 8 logs and more.
Any suitable kinase enzyme may be used as the reporter kinase in the present invention. In one embodiment, the reporter kinase is an adenylate kinase, acetate kinase or pyruvate kinase, or a combination thereof.
The reporter kinases used in the invention may have a variety of recognized tertiary structures, e.g., the kinase may be a trimeric or monomeric kinase. These tertiary structures may be associated with an improved stability of the kinase to conditions such as e.g., temperature, pH, chemical denaturants, or proteases.
In one embodiment, the reporter kinase is a microbial kinase derived from an organism selected from the group consisting of Pyrococcus furiousus, P. abyssi, P. horikoshii, P. woesii, Sulfolobus solfataricus, Sacidocaldarius, S. shibatae, Rhodothermus marinus, Thermococcus litoralis, Thermatoga maritima, Thermatoga neapolitana and Methanococcus spp. In another embodiment, the kinase is a Sulfolobus sp. kinase or a Thermotoga sp. kinase. In yet another embodiment, the kinase is a A. acidocaldarius kinase, A. fulgidus kinase, A. pernix kinase, A. pyrophilus kinase, B. caldotenax BT1 kinase, Bacillus species PS3 kinase, B. stearothermophilus 11057 kinase, B. stearothermophilus 12001 kinase, B. thermocatenulatus kinase, C. stercocorarium kinase, Methanococcus spp. Kinase, M. ruber kinase, P. abyssi kinase, P. furiosus kinase, P. horikoshii kinase, P. woesii kinase, R. marinus kinase, S. acidocaldarius kinase, S. shibatae kinase, S. solfataricus kinase, T. ethanolicus kinase, T. thermosulfurogenes kinase, T. celere kinase, T. litoralis kinase, T. aquaticus YT1 kinase, T. caldophilus GK24 kinase, T. thermophilus HB8 kinase, T. maritima kinase or a T. neapolitana kinase. In yet a further embodiment, the kinase is a T. litoralis kinase, T. maritima kinase, or a T. neapolitana kinase.
In one embodiment, the reporter kinase is thermostable. As well as being resistant to high temperatures, thermostable kinases are also found to be resistant to other biochemical and physical processes that routinely damage or destroy proteins or render them inactive, such as exposure to certain chemicals e.g., chaotropes, free-radical damage, detergents, extremes of pH, exposure to proteases, protein cross-linking, encapsulation within non-permeable or semi-permeable membranes or polymers, or irreversible immobilisation onto surfaces. (See for example: Daniel R M, Cowan D A, Morgan H W, Curran M P, “A correlation between protein thermostability and resistance to proteolysis”, Biochem J. 1982 207:641-4; Rees D C, Robertson A D, “Some thermodynamic implications for the thermostability of proteins”, Protein Sci. 2001 10:1187-94; Burdette D S, Tchernajencko V V, Zeikus J G. “Effect of thermal and chemical denaturants on Thermoanaerobacter ethanolicus secondary-alcohol dehydrogenase stability and activity”, Enzyme Microb Technol. 2000 27:11-18; Scandurra R, Consalvi V, Chiaraluce R, Politi L, Engel P C., “Protein thermostability in extremophiles”, Biochimie. 1998 November; 80(11):933-41; and Liao H H., “Thermostable mutants of kanamycin nucleotidyltransferase are also more stable to proteinase K, urea, detergents, and water-miscible organic solvents”, Enzyme Microb Technol. 1993 April; 15(4):286-92, all of which are hereby incorporated by reference in their entirety).
Examples of kinases suitable for use in the invention are set out in SEQ ID NO.s 1-32 below. In one embodiment, the kinases used in the invention have at least 70%, 80%, 85%, 90%, 95%, 99% or 100% identity to SEQ ID Nos: 1-32.
Other examples of suitable reporter kinases may be found in WO00/46357 and WO2005/093085, which are hereby incorporated by reference in their entirety.
In one embodiment of the invention, kinase activity is detected using an ATP bioluminescent detection system. A standard luciferin-luciferase assay method can detect as little as 10−15 moles of ATP. By coupling an enzymatic amplification to the bioluminescent detection methods it is possible to detect as few as 10−20 moles of kinase.
Stabilisation of the Biological Indicator
A number of additives and changes to formulation that increase the stability of an enzyme, e.g., a kinase, to heat inactivation will be known to those familiar with the art.
The addition of stabilising agents such as sorbitol up to a concentration of 4M, or other polyols such as ethylene glycol, glycerol, or mannitol at a concentration of up to 2M may improve the thermostability of the enzyme. Other additives such as xylan, trehalose, gelatin may also provide additional stabilisation effects either individually or in combination. Addition of a range of divalent metal ions, most notably Ca2+, Mg2+ or Mn2+ may also improve stability of the enzyme.
Chemical modification of the enzymes can also be used to improve their thermal stability. Reductive alkylation of surface exposed amino groups by glyoxylic acid (e.g Melik-Nubarov (1987) Biotech lefts 9:725-730), addition of carbohydrates to the protein surface (e.g., Klibanov (1979) Anal. Biochem. 93:1-25) and amidation (e.g., Klibanov (1983) Adv. Appl. Microbiol. 29:1-28) may all increase the stability of the enzyme. Further methods including the use of chemical cross-linking agents and the use of various polymeric supports for enzyme immobilisation are also relevant methods for increasing the thermostability of enzymes (reviewed in Gupta (1991) Biotech. Appl. Biochem. 14:1-11).
Similar modifications are also relevant to the stabilisation of the indicator against other sterilisation processes such as hydrogen peroxide or ozone. In particular, processes where the access of the gaseous phase sterilant to the enzyme is restricted, for example by encapsulation in a suitable polymer or formulation with an additive to reduce penetration of the gas, will provide useful methods for increasing the stability of the enzyme if required.
Many of the treatments that are effective at increasing the thermal stability of enzymes are also relevant to the stabilisation against protease treatments, e.g., for the development of an indicator for the effective inactivation of TSE agents by protease treatment. In general, a protein that shows high levels of thermostability is likely to also show a high degree of stability for degradative processes such as denaturation or protease treatment (See for example: Daniel R M, Cowan D A, Morgan H W, Curran M P, “A correlation between protein thermostability and resistance to proteolysis”, Biochem J. 1982 207:641-4; Rees D C, Robertson A D, “Some thermodynamic implications for the thermostability of proteins”, Protein Sci. 2001 10:1187-94; Burdette D S, Tchemajencko V V, Zeikus J G. “Effect of thermal and chemical denaturants on Thermoanaerobacter ethanolicus secondary-alcohol dehydrogenase stability and activity”, Enzyme Microb Technol. 2000 27:11-18; Scandurra R, Consalvi V, Chiaraluce R, Politi L, Engel P C., “Protein thermostability in extremophiles”, Biochimie. 1998 November; 80(11):933-41; and Liao H H., “Thermostable mutants of kanamycin nucleotidyltransferase are also more stable to proteinase K, urea, detergents, and water-miscible organic solvents”, Enzyme Microb Technol. 1993 April; 15(4):286-92). Thermostable kinases therefore generally show a higher degree of stability to the actions of the protease treatments designed to inactivate TSE agents than might equivalent mesophilic kinases. Depending on the type of process used, a kinase can also be selected to favour other characteristics of the process. Thus for a protease treatment at alkaline pH the protocol tends towards the use of a thermostable kinase from a moderately alkalophilic organism such as P. furiosus, whereas a protease treatment at acidic pH might use a kinase from an acidophile such as S. acidocaldarius or S. solfotaricus.
If required to improve the stability of the kinase indicator to protease treatment a number of other options exist. A number of these are the same as those described above for the stabilisation of the enzyme against heat treatment. For example, formulations containing sorbitol, mannitol or other complex polymers reduce the levels of inactivation of the enzyme on the indicator surface. In addition, treatments that specifically reduce the rate at which a protease substrate is degraded are particularly relevant to this application. For example, the formulation of the kinase in a solution containing up to around 10 mg/ml (a 10-fold excess compared to the preferred concentration of the indicator) of a suitable carrier protein such as casein or albumin, that acts as alternative substrate for the protease, will specifically reduce the rate of digestion of the kinase indicator. Similarly, the addition of free amino acids such as glycine, tyrosine, tryptophan or dipeptides to the formulation would provide a means of substrate level inhibition of the enzyme and reduce local inactivation of the kinase indicator.
Thermostable kinases produced by recombinant expression in bacteria can also be used in the present invention. The genetic modification of enzymes has been shown to provide significant increases in thermal stability and by analogy such mutations are also likely to significantly enhance the stability of the indicator enzymes in other processes such as protease treatment or gaseous phase “sterilisation”. The comparison of the thermostability of the kinase enzymes taken with the defined 3-D structure of the trimeric (archaeal) AKs (Vonrhein et al. (1998) J. Mol. Biol. 282:167-179 and Criswell et al. (2003) J. Mol. Biol. 330:1087-1099) has identified amino acids that influence the stability of the enzyme.
Genetically engineered variants of kinases showing improved thermostability are also used in the invention, and can be generated in a number of ways. Essentially these involve the specific site-directed mutagenesis of amino acids believed to form part of the central core packing region of the trimeric molecule and random “directed evolution” methods where the whole molecule is subjected to subsequent rounds of mutagenesis and selection/screening of molecules with improved properties. Specific modified enzymes are set out in SEQ ID NOs: 17-19 (several variants are embraced by each reference). These modifications outlined are based on a hybrid approach using a consensus based approach to define regions likely to influence the thermostability of the enzymes based on observed differences between structurally related molecules. This is followed by either defined changes to incorporate the amino acids that correlate with the best thermostability or a random replacement to incorporate every available amino acid at the positions defined as being essential for thermostability.
The stability/resistance of the indicators that bind to biological components that are part of a matrix may be improved by increasing the concentration of the biological component in the matrix, or by increasing the degree of cross-linking. By way of example, one of the indicators of the invention employs a fibrin-reactive peptide-kinase indicator to effect cross-linking into a biological matrix containing fibrin, e.g., a fibrin film. By altering the fibrin film, e.g., by increasing the concentration of fibrin, or by increasing its degree of cross linking, it is possible to significantly increase the resistance of the indicator to specific processes.
The resistance of indicators containing biological components such as Sup35 can be increased by promoting the fibrilisation of the indicators. This provides a molecule with greater physical stability, and may be relevant to monitoring the inactivation of agents such as prion proteins, which are believed to be multimeric in nature.
In one embodiment, the indicator is formulated in a carrier selected from the group consisting of sucrose (e.g., at up to 1% w/v), mucin (e.g., at up to 0.5% w/v), and albumin (e.g., at up to 1 mg/ml).
Solid Supports
The biological indicator of the invention may be attached to a variety of solid supports. The supports may be with or without chemical modifications and may comprise one or more indicators in a variety of formulations, depending e.g., on the requirements of the process to be validated. In one form the support is a plastic, wood, ceramic, glass, textile, steel or other metallic or polymer surface onto which the indicator is dried/cross-linked as a means of immobilisation. The support can be a polycarbonate, polystyrene or polypropylene strip or dipstick, optionally with a flattened surface, onto which the indicator is applied. An additional type of support with a porous surface for attachment of indicator is also particularly useful as an indicator for gaseous processes. Plastic, wooden, metallic or ceramic beads may also provide a valuable format for the solid support, again with specific relevance to monitoring gaseous processes. Such supports have advantages for certain applications, as they provide a significantly increased surface area for the attachment of the indicator. In a further embodiment, the solid support is a matrix and the indicator is dispersed within the matrix. In yet another embodiment, the matrix is a complex biological matrix.
Immobilisation of the Biological Indicator onto the Solid Support
The indicators of the invention may be bound onto the solid support using any of a wide variety of methods known in the art.
In one embodiment of the invention, the indicator is bound onto the solid support via standard protein adsorption methods as outlined below.
Binding of the indicator onto the solid support may be achieved by methods routinely used to link protein to surfaces, e.g., incubation of protein in 0.1M sodium bicarbonate buffer at about pH 9.6 at room temperature for about 1 hour. Alternatively, the protein is covalently coupled to the surface using any of a wide range of coupling chemistries known to those familiar with the art. For example, an adenylate kinase fusion protein (e.g., to Sup35) derivatised with SPDP (Pierce chemicals; using manufacturer's instructions), reduced with DTT to provide free sulfhydryl groups for cross-linking, is covalently attached to a polystyrene support with a maleimide surface. Plastic surfaces with such sulfhydryl-binding surfaces are well described in the literature. An added benefit of this method of coupling is that, if required, the enzyme can be cleaved from the support, e.g., by reduction with DTT or MESNA, to allow the assay to be carried out separately to any indicator support. The indicators described in this application have the property that their activity is retained upon derivatisation and cross-linking to such supports.
Alternatively, an amine reactive surface on a polystyrene or polycarbonate support is used, with a bifunctional cross-linking agent such as monomeric glutaraldehyde, to provide direct non-cleavable cross-linking of the kinase indicator via free amine groups on the protein. UV treatment can also be used to directly link the indicator to a suitable support. Steel surfaces can be treated in a similar way to plastic surfaces to mediate covalent attachment of the indicator.
A wide variety of protein cross-linking reagents are available from companies such as Pierce chemical company (Perbio). Reagents reactive to sulfhydryl, amino, hydroxyl and carboxyl groups are designed for coupling proteins but they can equally be used for cross-linking proteins to either naturally reactive or coated solid supports such as plastics, other polymers, glass and metals. Reactive chemistries are also available for cross-linking the enzymes to carbohydrates. For example, the reagents BMPH ((N-[ß-maleimidopropionic acid]hydrazide.TFA), KMUH ((N-[k-maleimidoundecanoic acid]hydrazide), and MPBH (4-(4-N-maleimidophenyl)butyric acid hydrazide hydrochloride) can be used to cross link the indicator containing either a free sulfhydryl in the form of a cysteine residue or a chemically derivatised protein reduced to generate a sulfhydryl reactive group, to carbohydrates. This may be particularly important for a solid support which is either a complex carbohydrate (e.g., paper, cellulose-based membranes, gels or resins) or can be coated or treated with a carbohydrate solution to generate a suitably reactive surface.
For each type of support, the indicator may be formulated in a solution that enhances binding and/or stabilises the bound protein. Such formulations include solutions containing up to 10% (w/v) sucrose, sorbitol, mannitol, cellulose, or polyethylene glycol (PEG). In addition, the indicator can be formulated as part of a gel that is applied to the surface or lumen of a suitable support. Examples include alginate, agar or polyacrylamide matrices.
The indicator may also comprise an agent to stabilise the indicator, and suitable stabilising agents are selected from metal ions, sugars, sugar alcohols and gel-forming agents.
To facilitate use of the indicator, the indicator may further comprise means to attach the solid support to a surface, such as a projection, recess or aperture for attachment of the support to a surface by means of a screw, nut and bolt or clamp.
Kits Comprising the Biological Indicator
In a second aspect of the invention, there is provided a kit for use in validating a treatment process in which the amount or activity of a contaminant in a sample is reduced, comprising:
To carry out measurement of the kinase amount/activity, the kit can include means for detecting ATP, e.g., luciferin/luciferase and optionally a luminometer. In one embodiment, the substrate for the thermostable kinase is ADP.
From previous testing with known contaminants, data correlating the reduction in the amount or activity of the contaminant with kinase activity can be prepared, and the kit therefore can also include one or more look-up tables correlating kinase activity with the reduction in amount or activity of a list of specified contaminants. In one embodiment, the kit is for monitoring TSE inactivation. In a further embodiment, the kit is used for monitoring norovirus inactivation.
Use of the Biological Indicator
In a third aspect, the invention provides for the use of a thermostable kinase covalently linked to a biological component as a biological process indicator for validating a treatment process for reducing the amount or activity of a contaminant in a sample.
In one embodiment, the biological process indicator is formulated according to the first aspect of the invention.
In a particular use of the invention, an indicator according to the first aspect of the invention is the reporter in a method of indicating the possible presence of a contaminant (e.g., an infectious agent) following a cleaning or inactivation procedure. First, a sample containing the indicator is exposed to a cleaning/inactivation procedure (e.g., one or more of a selected temperature, pH or protease concentration). The next step is to remove any contaminating enzymatic activity by heat treatment, e.g., at from 60° C. to 80° C. for at least 10 minutes (i.e. under conditions that do not significantly affect the thermostable kinase). The indicator is then reacted at a temperature of between 30° C. and 70° C. with a substrate (e.g., ADP) to allow the generation of ATP. The formation of ATP can be measured by bioluminescent detection using luciferin/luciferase and a suitable luminometer at 20° C.-30° C. for 10 minutes to 1 hour. The light output reading from the luminometer gives a reading of the residual kinase activity, i.e. the activity of the kinase following exposure to the cleaning/inactivation treatment. Based on data that have been previously derived from separate experiments, the method is completed by correlating the residual kinase activity with the possible presence of a contaminant within the treated sample.
In one embodiment, contaminating enzymatic activity or ATP in a sample may be removed by an initial treatment step (e.g., a selected temperature, pH or protease concentration), prior to addition of the indicator.
The use of the indicator of the invention to monitor/validate a variety of processes is now described.
In one embodiment, the indicator is used to validate the performance of a biological washing preparation in a wash cycle. Whilst validation of a wash cycle would potentially be of use in a domestic setting, its most advantageous use would be within a healthcare, pharmaceutical or food preparation setting, e.g., for validating decontamination of bedclothes, gowns or other items associated with patients suffering or exposed to infectious agents (e.g., an outbreak of methicillin resistant Staphylococcus aureus (MRSA) or Norwalk/Norwalk-like virus). In this context, the indicator of the invention has the advantage that it is relevant to biological material such as blood or other bodily fluids.
For the validation of a wash cycle, the indicator may be cross-linked onto a flexible wand, strip of cloth or other material suitable for inclusion within the cycle. The indicator is put into the washer with the remainder of the load. In one embodiment, the indicator may be fixed within a suitable holder on the inside of the washer to facilitate its recovery.
The wash cycle is then performed and the indicator removed and assessed prior to any further handling or processing of the load, using a “reader” which has been calibrated to indicate an acceptable level of residual kinase activity within the indicator—the acceptable level having been derived from previous calibration and assessment of suitable wash performance within the process. Such assessment might include the overall levels of soiling and the viable count of micro-organisms as assessed using suitable model organisms known to those familiar with the art. Based on the calibrated read-out, the load is passed for further processing or the wash cycle is repeated.
In a second embodiment, the indicator is used to validate processes for the inactivation of viruses. The detection of live viral isolates in the environment is problematic, particularly when associated with an emergency situation where speed and accuracy may be critical. The present invention provides the possibility of developing indicator systems that allow the monitoring of decontamination procedures essentially in real time. This would be particularly valuable for surface decontamination in healthcare and related facilities following either an outbreak (e.g., of Norwalk-like viruses) or a deliberate release of a viral agent (such as small pox).
An indicator for validating a viral inactivation process can take a variety of different forms, e.g., a wand or dipstick for monitoring an area sprayed or immersed with virucide, or a suspended indicator for monitoring a gaseous phase decontamination process. Alternatively, the indicator can be sprayed onto a surface prior to decontamination and the levels of residual kinase activity subsequently assessed by swabbing of the surface.
In a further embodiment of the invention, the indicator is used for validating protease degradation of bacterial protein toxins, plant toxins such as ricin, and other toxic proteins, peptides, or peptide analogues.
Proteases show significant potential for the degradation of a wide range of protein toxins that are potential biowarfare/bioterror threat agents including botulinum toxin, anthrax toxins and ricin. They also have the potential to inactivate a wide range of other potentially toxic or harmful protein or peptide agents to enable decontamination of surfaces/facilities or the safe disposal of materials. In this context, the indicator of the invention, together with the surface/material to be decontaminated, is subjected to the protease decontamination procedure. At the end of the procedure, the residual kinase activity of the indicator is assessed according to the method of the invention. The level of residual kinase activity is then correlated with inactivation indices for the particular protein toxin, or group of toxins. Assuming the level activity is equal to or below the defined index value then the material can be safely disposed of or the surface/facility returned to use.
In one embodiment, a suitable safety margin is built into the calibration of the inactivation indices to allow for any variability of the process performance. The additional stability of the enzymes used in this invention allow for this to be done with more certainty and greater dynamic range than a wide range of other enzymatic indicators, including those from “thermostable” organisms such as Bacillus stearothermophilus, as shown by the data showing the relative thermal stability of AKs from thermophilic organisms (
The indicator may also be used to validate protease decontamination procedures for cleaning down pharmaceutical production apparatus. A wide variety of pharmaceutical products use materials from either humans, or animals that might be contaminated with a wide variety of agents including prion (TSE) agents and viruses (e.g., West Nile virus, hepatitis, HIV). The risks may be exacerbated when the source of the material is of animal origin (e.g foetal calf serum, horse immunoglobulins) and where an intermediate processing stage may carry the risk of increasing the concentration of unidentified pathogens in a particular sample. The possibility of using a protease to clean down manufacturing facilities and apparatus (e.g., chromatography columns, vessels, pipework) between manufacturing batches has the potential to reduce or eliminate such risks, even when the contaminant has not been formally identified. This is particularly true for prion agents in, for example, blood fractionation apparatus where there is a significant risk of accumulation and of carrying an infection risk into the final product.
For validating this type of procedure, the indicator of the invention is ideally formulated as a dipstick to be immersed in the protease treatment solution, or as a cartridge to be attached in line with the apparatus to be cleaned. By assessing the levels of residual kinase activity in the indicator device following the treatment, and correlating this with the acceptable levels of cleaning, a rapid and reliable monitor of performance can be developed.
In another embodiment of the invention, the indicator is used for validating gas phase inactivation of contaminants, such as TSE.
The potential of ozone or other gas phase sterilants to inactivate such contaminants is suggested by a wide range of publications and articles, however, as yet, no method has explicitly been shown to be effective. To support the development and introduction of this gas phase technology into healthcare, a means of validating the performance of the technology will be required. As agents such as TSE have already been shown to be far more resistant to this form of inactivation than conventional viral or bacterial agents, the methods currently available for validating gas phase inactivation are unlikely to be suitable. The present invention addresses this problem.
For this type of validation, the indicator is attached onto a solid support by any suitable method, e.g., general adsorption and chemical cross-linking via amide, peptide, carbonyl, or cysteine bonds. For example, for ozone sterilisation, a rigid polyvinyl chloride (PVC), glass, steel, polyamide or polypropylene support may be used, with the indicator coupled to the support by any one of the methods previously described. The indicator is then included in the batch of material/instruments to be sterilised, exposed to the ozone, and assessed against a suitably calibrated inactivation index designed for assessing corresponding inactivation of the agent in question. Successful inactivation allows onward processing or use of the material/instruments.
The indicator may optionally be attached to the internal face of a tube or equivalent internal space, such that the penetration of the gas is restricted. This provides for a monitor that is suitable for assessing the penetration of the gas into equivalent spaces in instruments with lumens, or through packed loads of material. Alternatively, the indicator may be attached to porous materials such as polystyrene beads, or may be immobilised within a gel or resin.
In a further embodiment of the invention, the indicator is used for validating liquid chemical sterilisation systems (e.g., ENDOCLENS-NSX™) as used for processing of endoscopes and related equipment.
A wide range of endoscopes are routinely used in medicine and are an important part of medical diagnosis and treatment. These instruments are extremely sensitive and have posed a very significant problem for routine cleaning and disinfection. Traditionally, and remaining in current practice, endoscopes are cleaned by hand before being decontaminated using a low temperature method. A range of chemical disinfectants and automated re-processing apparatus has been developed to address the specific issues of decontaminating sensitive pieces of equipment such as endoscopes, where traditional autoclaving is not possible. These methods have helped to reduce the levels of contamination on difficult to clean instruments, which have been associated with the iatrogenic transmission of a wide range of viral and bacterial pathogens. The current method of validating such processes is to monitor the flow rate and temperature of the washing solution. The indicator of the invention provides for a further means of validation that provides a read-out of actual cleaning effectiveness within the endoscope lumen.
For this type of validation, the indicator is attached to the internal surface of a tube designed to be of a similar overall internal diameter to the endoscope tube. This indicator apparatus is connected in series to the endoscope on the automatic reprocessing apparatus. The endoscope is then processed in the normal way. At the end of the process, preferably before the endoscope is removed from the apparatus, the indicator is detached and assessed for the level of kinase activity remaining. The level of activity may be correlated with previously defined thresholds for the acceptable performance of the process and, based on this assessment, the endoscope may be transferred for additional cleaning or decontamination or prepared for use. If the level of performance is not adequate then the instrument may be re-processed (using the same or more stringent conditions) with a new indicator attached as previously. The indicator apparatus is also suitable for validating the manual cleaning of endoscope and/or any other instrument with a lumen.
In a further embodiment of the invention, the indicator is used to monitor routine cleaning performance in washer-disinfectors, such as those used in hospitals.
In another embodiment of the invention, the indicator is used for monitoring glutaraldehyde or ortho-phthaldehyde (OPA) treatments. Glutaraldehyde and formaldehyde have been widely used as sterilants over many years. The chemical disinfectants work by multiply crosslinking proteins in a non-specific fashion to destroy their function. Ortho-phthaldehyde (OPA) has emerged recently as a new disinfectant in this family and is being widely used as it avoids some of the toxicity problems associated with glutaraldehyde. The indicator of the invention is suitable for the monitoring of all of this class of chemical disinfectants as the kinases are sensitive to non-specific cross-linking of this kind. The indicator may be covalently attached to a suitable surface and exposed to the chemical sterilant along with the other items to be sterilised. The effectiveness of the process is assessed by measuring the residual enzyme activity of the indicator. This activity is compared to defined threshold values that indicate the correct performance of the process.
The use of different types of kinase may provide additional sensitivity or susceptibility to the process as may be required for different applications. The thermostable adenylate kinases described in this specification can be broadly classified into two groups based on their molecular architecture. Thus, the enzymes from Sulfolobus species are examples of enzymes that have a trimeric structure with a central hydrophobic core that is the principle determinant in maintaining their activity at high temperatures. The second group of enzymes are monomeric, exemplified by the adenylate kinases from Thermatoga species, but have a slightly longer polypeptide chain with an additional “lid” domain that affects the active site. These different types of thermostable enzymes will show differential sensitivity to this type of chemical sterilant due to the variable flexibility of their peptide chains during enzyme action. For any particular sterilant and/or concentration an empirical screen will identify enzymes with suitable susceptibilities for monitoring and validating these types of chemicals.
In a further embodiment of the invention, the indicator is used as an ultra-rapid read-out monitor for ethylene oxide, hydrogen peroxide or other gas phase processes.
A wide range of gas phase sterilants are currently being used by a variety of manufacturers for routine disinfection of bacterial and viral agents. The current methods exploit the oxidative properties of the gases to destroy peptide linkages. As such, the kinases of the present invention, with their robust physicochemical properties, are ideal for providing a very rapid read-out of inactivation. The indicator in this example is similar to those described previously, e.g., in relation to the ozone inactivation of agents such as TSE.
A particularly challenging issue for sterilisation and decontamination processes is the ability to validate sterility of large bulk liquids, as might be required in the manufacture of various medicines or other pharmaceutical products. Whilst current methods monitor the temperature, time, and/or pressure parameters of a particular process (depending on its precise nature), there are few, if any, available methods for validating actual sterilisation within the bulk liquid. This is difficult even within volumes of around 1 liter, but is almost impossible at larger volumes.
The present invention provides a number of possible solutions to address this problem. In its simplest form, the indicator may be added to the liquid to be sterilised at a concentration suitable for measuring defined levels of kinase inactivation at the end of the process and equating this to levels of sterilisation. Whilst this might not be desirable in certain types of processes, the inert nature of the kinase and the ubiquitous presence of equivalent enzyme activities in all organisms, may make it acceptable. The acceptability may be improved by the fact that many thermostable enzymes are highly condensed and thus have very low immunogenicity following inoculation into animals.
Where such direct additions are not acceptable, the indicator may be added to the bulk liquid in a dialysis sack, porous container or immobilised to a suitable support such that no part of the indicator is released into the bulk liquid, but the sterilising conditions work on the indicator in the same way as for the whole sample. A wide variety of possible ways of containing or immobilising proteins, to allow general diffusion of the liquid sample but to restrict the movement of the indicator sample, will be known to those familiar with the art. Possible examples include, but are not limited to dialysis membranes, Visking tubing, porous membranes, protein-binding resins, rigid gels or solid supports as described for the other indicators discussed. The indicator may be attached to the surface by any one of the methods discussed previously, or simply encased within a suitable membrane without attachment, such that the indicator may be simply removed from the bulk liquid at completion of the process.
Method of Validating a Treatment Process
In a fourth aspect, the invention provides a method of validating a treatment process for reducing the amount or activity of a contaminant in a sample, comprising the steps of:
It is possible that the sample in step (a) may not contain any contaminant at all. The point of the validation is that, after carrying out the treatment, it is confirmed that any agent that might have been present has been removed/inactivated to an acceptable degree. In general, however, the sample is known to contain, or suspected to contain, the contaminant.
In one embodiment, the thermostable kinase used in step (b) of the method is formulated as an indicator according to the first aspect of the invention.
In another embodiment, the residual kinase activity in step (c) is measured by adding a substrate comprising ADP to the residual kinase and measuring the formation of ATP. ATP formation can be measured by bioluminescent detection using luciferin/luciferase and a suitable luminometer.
Typically, an operator measures kinase activity before and after treating the sample. It is also possible that contaminating, usually mesophilic, kinase can get into the sample prior to assaying for kinase activity. Thus, in one embodiment of the invention, the assay includes the step of inactivating mesophilic kinase, such as by treating the sample at 70° C. for at least 30 minutes, or at 80° C. for at least 10 minutes, prior to measuring residual kinase activity.
In one embodiment, the kinase, prior to the treatment, has an activity of at least 10,000,000 Relative Light Units (RLU) per mg kinase, or at least 8,000,000 RLU per mg kinase, or at least 5,000,000 RLU per mg kinase, or at least 3,000,000 per mg kinase, or at least 1,000,000 RLU per mg kinase, or at least 500,000 RLU per mg kinase, when measured in the presence of luciferin/luciferase by a luminometer.
In another embodiment of the invention, the predetermined kinase activity is less than 10,000 RLU per mg kinase, or less than 1000 RLU per mg kinase, or less than 500 RLU per mg kinase, or less than 250 RLU per mg kinase, or less than 100 RLU per mg kinase, or less than 10 RLU per mg kinase, or less than 1 RLU per mg kinase, or is 0 RLU per mg kinase.
In a further embodiment of the invention, the predetermined reduction in kinase activity is equal to or greater than a 1 log reduction, or a 2 log reduction, or a 3 log reduction, or a 4 log reduction, or a 5 log reduction, or a 6-log reduction, or a 7 log reduction, or an 8 log reduction or a 9 log reduction in kinase activity.
In another embodiment, the predetermined reduction in kinase activity corresponds to a 3 log reduction, or a 6 log reduction, or a 7 log reduction, or an 8 log reduction, or a 9 log reduction, in the amount or concentration of the kinase. In further embodiments, the predetermined reduction in kinase activity corresponds to a reduction in RLU of at least 800,000, or at least 900,000, or at least 950,000, or at least 990,000, or at least 999,000, or at least 999,900, or at least 999,990, or at least 999,999 RLU.
In yet another embodiment of the invention, the confirmed reduction in the amount or activity of the contaminant within the sample is at least 3 logs, at least 6 logs, ably at least 7 logs, more ably at least 8 logs, most ably at least 9 logs.
In another embodiment of the invention, the treatment is continued until the residual kinase activity or the reduction in the kinase activity corresponds to a confirmed reduction in the amount or activity of the contaminant of at least 3 logs, at least 6 logs, or at least 7 logs, or at least 8 logs, or at least 9 logs.
In one embodiment of the invention, the method further comprises the step of recording the data obtained in step (c) on a suitable data carrier.
Method of Correlating
In a fifth aspect, the invention provides a method of correlating the reduction in the amount or activity of a contaminant in a sample with the kinase activity of a biological process indicator as described in connection with the first aspect of the invention. This method comprises:
In one embodiment, the treatment parameter comprises one or more of time, temperature, pH, pressure, protease concentration, and concentration of sterilant or detergent.
In a particular embodiment, the treatment comprises heating the sample(s) at 50-140° C., or 80-100° C., or 134-138° C.; the treatment parameter is time; and steps (i) to (iv) are repeated by subjecting the sample(s) to said treatment for periods of 1, 5, 10, 20, 40 and 60 minutes.
In a further embodiment, the treatment comprises exposing the sample(s) to a pH of 9-14, or pH 12 or above, or about pH 12; the treatment parameter is time; and steps (i) to (iv) are repeated by subjecting the sample(s) to said treatment for periods of 1, 5, 10, 20, 40 and 60 minutes.
In another embodiment, the treatment comprises exposing the sample(s) to a protease at a concentration of 0.5-2 mg/ml, or about 1 mg/ml, or about 2 mg/ml; the treatment parameter is time; and steps (i) to (iv) are repeated by subjecting the sample(s) to said treatment for periods of 1, 5, 10, 20, 40 and 60 minutes.
The above method enables preparation of calibration data for future use of the indicator for validation of a treatment on samples containing, or suspected of containing contaminant. The calibration of a number of treatment processes is described in WO2005/093085.
The term “contaminant” encompasses both infectious and non-infectious agents derived from a biological source. Examples of contaminants include bacteria, viruses, fungi, prions, toxins, allergens, spores, any of the agents listed above as biological components, and fragments and derivatives of any of the foregoing. In the context of the invention, a contaminant can also be referred to as a contaminating biological agent.
The term “cross-linked” refers to the attachment of two entities via one or more covalent bonds. Cross-linking may be chemical or genetic. Genetic cross-linking encompasses indicators prepared as fusion proteins.
The term “sample” encompasses any item, instrument, surface, fluid or material. Examples include, but are not limited to clinical samples (such as whole blood, serum, oral samples such as saliva, pus, vaginal samples, stool samples, vomitus), environmental samples (such a water, soil, air samples), surgical and medical instruments, microtitre plates, dipsticks, lateral flow devices, hospital gowns, bedclothes, bulk liquids, culled animal material, pharmaceuticals, workbenches, walls and floors, biological matrices.
The term “treatment” or “treatment process” encompasses any process that is designed to reduce the amount or activity of a contaminant in a sample. Suitable treatments include one or more of: a selected pH (e.g., below pH 1, 2, 3, 4, 5, 6 or 7, or above pH 7, 8, 9, 10 or 11, or about pH 12), temperature (e.g., at least 40 C, 50 C, 60 C, 70 C, 80 C, 90 C, 100 C, 110 C, 120 C, 130 C, 140 C, 150 C, or 160 C, or between 50-120 C) or pressure (e.g., at least 50 kPa, 70 kPa, 100 kPa, 150 kPa, 200 kPa, or 250 kPa), exposing the sample to a protease or other lytic enzyme, exposing the sample to a detergent, a chemical sterilant, radiation, free radicals, or a gas-phase sterilant. In one embodiment, the treatment is designed to reduce the infectious activity (also known as the infectivity) of an infectious biological contaminant, such as TSE. The term “treatment” or “treatment process” also encompasses cleaning and inactivation processes such as high temperature autoclaving with wet or dry steam, ozone sterilisation, H2O2 sterilisation, rendering or other method designed to eliminate or inactivate the contaminant. In another embodiment of the invention, both the indicator and the contaminant are directly exposed to the treatment process, i.e. there is no seal or barrier between the indicator/contaminant and the treatment process. The indicator and the contaminant are therefore both in direct contact with the treatment process, and are subject to the same treatment conditions.
The term “biological component” encompasses any biological molecule that can be covalently linked to a kinase enzyme. The biological component may be selected from a protein, a nucleic acid, a lipid or a carbohydrate. The biological component is suitably a mimetic or surrogate of the contaminant in the sample to be treated, and therefore reacts to the treatment process in substantially the same way as the contaminant. In one embodiment, the biological component may be the same as, but physically distinct from, the contaminant in the sample that is to be subjected to the treatment process, e.g., if the contaminant is a protein, then the biological component is also a protein; if the contaminant is a blood protein, the biological component is also blood protein; if the contaminant is a DNA molecule, then the biological component is also a DNA molecule; if the contaminant is an RNA molecule then the biological component is also an RNA molecule, etc. for each of the contaminants and biological components disclosed in this specification. In another embodiment, the biological component is different from the contaminant. In one embodiment of the invention, the biological component is not a peptide, protein or polypeptide. In a further embodiment of the invention, the biological component is not an oligonucleotide (e.g., an oligonucleotide probe specific for HPV16). In yet a further embodiment of the invention, the biological component is not a lectin, growth factor, DNA/RNA aptamer, bacteriophage, or a binding agent specific for an analyte.
The term “protein” encompasses any protein- or peptide-containing molecule. The terms “protein”, “peptide”, and “polypeptide” are used interchangeably in the present specification.
The term “blood protein” encompasses any protein that is present in blood. Specific examples include blood clotting proteins (e.g., fibrinogen, fibrin peptides, fibrin, transglutaminase substrates, thrombin), serum proteins (e.g., albumin and globulin), platelets, blood cell glycoproteins, and haemoglobin.
The term “bacterial protein” encompasses any protein that is derived from a bacterium. Specific examples include a bacterial fimbrial protein (e.g CgsA from E. coli and AgfA from Salmonella), a bacterial toxin protein (e.g., toxins from Bacillus anthracis, Corynebacterium diphtheriae, Clostridium botulinum), a bacterial cell surface protein (e.g., cell surface adhesins from floc forming and filamentous bacteria in activated sludge, peptidoglycan, lipoproteins), and a bacterial spore protein (e.g., from Gram positive bacteria and having a similar sequence or overall structure to the proteins forming ribbon appendages in Clostridum taeniosporum, chaplin proteins A-H and rodlin proteins Rd1A and Rd1B from Streptomyces spp.)
The term “viral protein” encompasses any protein that is derived from a virus. Specific examples include a viral coat protein, a viral envelope protein, a viral capsid protein, and a viral core protein. In one embodiment, the viral proteins are from a bacteriophage virus (e.g., the MS2 and PP7 coat proteins), norwalk virus (e.g., capsid protein), rotavirus (e.g., VP2, VP6 and VP7 proteins), coronavirus (e.g., SARS S, E and M proteins), bluetongue (e.g., VP2 protein), human papillomavirus (e.g., viral major structural protein, L1), hepatitis B (e.g., small envelope protein HBsAg), Hepatitis C (e.g., core, E1 and E2 proteins), influenza (e.g., neuraminidase and haemagglutinin and matrix proteins), poliovirus (e.g., capsid VP0, 1 and 3 proteins), HIV (e.g., Pr55gag, envelope proteins) and dengue B (e.g., envelope (e) and pre-membrane/membrane (prM/M).
The term “fungal protein” encompasses any protein that is derived from a fungus. Specific examples include hydrophobin proteins (e.g., SC3 from Schizophyllum commune, RodA/B from Aspergillus fumigates, and equivalent proteins from yeast), fungal spore proteins, hyphal proteins, mycotoxins, and fungal prions (e.g., Sup35, Het S, Ure 2, Rnq1, New 1).
The term “self-aggregating protein” encompasses any protein that is capable of self-aggregating or self-assembling into amyloid fibrils or surface reactive biofilms. Specific examples include prions (e.g., PrPSc and PrPc, Het S, Ure 2, Rnq1, New 1), prion mimetic proteins, amyloid fibrils, cell surface adhesins from floc-forming and filamentous bacteria in activated sludge, beta amyloid protein, tau protein, polyadenine binding protein, lung surfactant protein C, CsgA protein from E. coli, AgfA protein from Salmonella species, bacterial fimbrial proteins, apolipoproteins (e.g., apolipoprotein A1), hydrophobins from fungal species (e.g., SC3 from Schizophyllum commune, RodA/B from Aspergillus fumigates), chaplins (e.g., Chps A-H from Streptomyces spp), rodlins (e.g., Rd1A and Rd1B from streptomyces spp), gram positive spore coat proteins (e.g., P29a, P29b, GP85 and a SpoVM analogue), and barnacle cement-like proteins (e.g., the 19 kDa protein from Balanus albicostatus, and the 20 kDa protein from Megabalanus rosa, and the novel calcite-dependent cement-like protein from Balanus albicostatus).
The term “nucleic acid” encompasses nucleotide polymers of any length or composition. Specific examples include a DNA molecule and an RNA molecule. In one embodiment, the nucleic acid is selected from single-stranded DNA (ssDNA), single-stranded RNA (ssRNA), double-stranded DNA (dsDNA) or double-stranded RNA (dsRNA). In another embodiment, said molecules are derived from neurological tissue.
The term “carbohydrate” encompasses any carbohydrate-containing molecule. Specific examples include exopolysaccharide, lipopolysaccharide, (EPS/LPS, sometimes known as endotoxin) (e.g., from Legionella, E. coli, Staphylococcus species, Streptococcus species, Pseudomonas species, Acinetobactor species, Campylobactor species, and Bacillus species,) peptidoglycan, cell wall components of plants, fungi and yeast (e.g., chitin, lignin, glucan), mucin preparations, glycolipids (especially brain derived glycolipids), glycoproteins (e.g., cell surface glycoproteins, Eap1p), spore extracts (e.g., from Bacillus spp, Clostridal spp and other spore-formers), polysaccharides from yeast capsules, and invertebrate secretions (e.g., from molluscan gels).
The term “lipid” encompasses any lipid-containing molecule. Specific examples include glycolipids (e.g., brain-derived glycolipids), gangliosides (e.g., GT1b, GT1a and GM1), and plant oils and lipids.
A “transglutaminase substrate” is any molecule that is a substrate for a transglutaminase enzyme. Transglutaminases are a family of enzymes (EC 2.3.2.13) that catalyze the formation of a covalent bond between a free amine group (e.g., protein- or peptide-bound lysine) and the gamma-carboxamid group of protein- or peptide-bound glutamine. Examples of such enzymes include Factor VIII, keratinocyte transglutaminase and tissue transglutaminase. Fibrin, which is acted upon by Factor VIII, is an example of a transglutaminase substrate.
A “biological matrix or mixture” may comprise one or more components selected from the group consisting of proteins, lipids, nucleic acids and carbohydrates. In one embodiment, it may be a mixture of proteins, or may comprise one or more of blood, serum, mucus, egg, neurological tissue, food, or culled animal material. The biological matrix or mixture may also be a commercially available test soil, such as Browne soil or Edinburgh soil. In one embodiment, the biological matrix/mixture has a similar composition to the matrix/mixture in which the contaminant is present. In the context of the invention, a biological matrix can also be referred to as a test soil.
A biological component that is a “mimetic” or “surrogate” of the contaminant is a component that will react to the treatment process in a very similar (or substantially the same) way to the contaminant. Similarly, a biological matrix that is a “mimetic” or “surrogate” of the sample is a matrix that has a similar composition to the sample, and that will react to the treatment process in substantially the same way.
The term “antibody” embraces full length immunoglobulins, and all fragments and derivatives thereof, e.g., a heavy chain, a light chain, a constant domain, a variable domain, an Fab region, an Fc region etc. of an immunoglobulin.
The term “fibrin” embraces all fibrin-derived peptides. This includes full length fibrin peptides and all fragments and derivatives thereof. It embraces all peptides having a fibrin reactivity, e.g., peptides that are acted upon by Factor VIII to form a clot. The term fibrin or fibrin peptide may be used interchangeably with the term “transglutaminase substrate” throughout this specification.
The term “light output” means the light that is emitted by the reaction of ATP with the bioluminescent reagent. This light output can be detected using entirely conventional technology, such as a standard luminometer (e.g., a Berthold Orion 96-well microplate luminometer, or a hand-held luminometer).
The term “reporter kinase” refers to a kinase enzyme that is not inherently present in the sample being tested, i.e. the kinase is exogenous to the sample. Reporter kinase is added to the sample as a separate reagent, e.g as an isolated kinase. In one embodiment, reporter kinases are thermostable.
The term “thermostable kinase” refers to a kinase that retains activity after exposure to heat, i.e. that is relatively unaffected by high temperatures. In one embodiment of the invention, thermostable kinases retain at least 70% activity (or 80% activity, 90% activity, 95% activity, or 100% activity) after exposure to a temperature of between 50-120 C. In another embodiment, thermostable kinases retain at least 70% activity (or 80% activity, 90% activity, 95% activity, or 100% activity) after exposure to 40 C for 30 minutes, or after exposure to 50 C for 30 minutes, or after exposure to 60 C for 30 minutes, or after exposure to 70 C for 30 minutes, or after exposure to 80 C for 20 minutes, or after exposure to 90 C for 10 minutes, or after exposure to 120 C for 3 minutes. Thermostable kinases may also be more resistant than non-thermostable kinases to a range of other biochemical and physical processes that routinely damage or destroy proteins or render them inactive, such as exposure to certain chemicals e.g., chaotropes, free-radical damage, detergents, extremes of pH, exposure to proteases, protein cross-linking, encapsulation within non-permeable or semi-permeable membranes or polymers, or irreversible immobilisation onto surfaces. In a particular embodiment, thermostable kinases may retain at least 70% activity (or 80% activity, 90% activity, 95% activity, or 100% activity) after exposure to one or more of the biochemical and physical processes described above. In all cases, this “retained activity” can be readily confirmed using conventional tests. In brief, the kinase is incubated with ADP under the given treatment conditions for a given amount of time, and then analysed for residual activity by detecting the generation of ATP using luciferin/luciferase and a luminometer. From this, the % of kinase activity retained after the treatment can be determined.
The terms “kinase” and “kinase activity” are used interchangeably throughout this specification.
The term “bioluminescent reagent” refers to any substance or mixture of substances able to react with ATP to generate light, e.g., a mixture of luciferin and luciferase.
The term “RLU” means Relative Light Unit. Relative Light Units are a relative, not absolute, measurement. The figures given in the specification relate to measurements taken using a Berthold Orion 96-well microplate luminometer with injector system using a “flash” method of light measurement for 2 seconds immediately after the addition of the luciferase/luciferin reagents (technical specification photomultiplier measuring light emitted at a wavelength of 300-650 nm). To address this issue, manufacturers have generated data for RLU “factors”, which allow the data generated by a given luminometer to be normalised to a calibrated standard. Thus, comparisons can be made between different instruments. The RLU factor for the Berthold Orion 96-well microplate luminometer is 1. Accordingly, the RLU values given in the specification can be regarded as standardised/normalised RLU values.
In terms of absolute values, an RLU value can be related to the concentration of ATP required to give said value with the reagents as described in the method. As an approximate conversion, and given the linear relationship between RLU values and ATP concentration, the following values can be used:
All references cited in this application are hereby incorporated by reference in their entirety.
The invention is now described in specific embodiments in the following examples and with reference to the accompanying drawings in which:
Lane 1, molecular weight markers; Lane 2, tAK conjugated to mucin; Lane 3, tAK-mucin conjugate reduced using DTT. Following SPDP derivatisation of tAK and mucin as described previously, high molecular weight conjugate species are formed <200 kDa. No non-conjugated tAK is present in Lane 2 demonstrating highly efficient cross-linking between the two protein species. Reduction of the conjugate breaks the cross-linking bonds resulting in the appearance of free tAK as indicated in Lane 3;
tAK in mucin was prepared by adding unmodified tAK to porcine mucin and allowing tAK to dry on the indicator surface. tAK-mucin conjugate was prepared as described previously using SPDP to cross-link tAK and mucin. The indicators were processed in a validated washer-disinfector using 3E-zyme as the detergent;
Purification of Native Adenylate Kinase Enzymes
Biomass was produced from twenty-four diverse thermophilic and hyperthermophilic microorganisms (Table 1).
Eight members of the archaea were represented along with sixteen diverse aerobic and anaerobic bacteria. AKs from each of these organisms was purified by affinity chromatography using selective absorption and desorption from Cibacron Blue 3A (Blue Sepharose). All enzymes were further characterised and purified by gel filtration (Superdex G200). This enabled identification of the major AK fraction and estimation of molecular mass.
Aeropyrum pernix
Alicyclobacillus acidocaldarius
Aquifex pyrophilus
Bacillus caldotenax BT1
Bacillus species PS3
Bacillus stearothermophilus 11057
Bacillus stearothermophilus 12001
Bacillus thermocatenulatus
Clostridium stercocorarium
Meiothermus ruber
Pyrococcus furiosus
Pyrococcus horikoshii
Pyrococcus woesei
Rhodothermus marinus
Sulfolobus acidocaldarius 98-3
Sulfolobus shibatae B21
Sulfolobus solfataricus P2
Thermoanaerobacter ethanolicus
Thermoanaerobacter
thermosulfurogenes
Thermobrachium celere
Thermococcus litoralis
Thermus aquaticus YT1
Thermus caldophilus GK24
Thermus thermophilus HB8
Analysis of Thermostability of Native Adenylate Kinases
The thermostability at 70° C., 80° C., and 90° C. of adenylate kinases isolated from biomass from thermophilic organisms was assessed, and the results shown in
The adenylate kinases were isolated from the biomass by affinity chromatography using selective absorption and desorption from Cibacron Blue 3A (Blue Sepharose). The samples eluted from the columns were diluted 1:10 000 and then 10 μl of each added to a microtitre well. 2.5 μl of apyrase was added to each well to destroy the ATP present from the elution buffer, and incubated at 37° C. for 30 minutes. The apyrase was inactivated by heat treatment at 65° C. for 20 minutes.
ADP substrate was added and incubated at either 70 (panel A), 80 (panel B) or 90° C. (panel C) for 30 minutes and cooled to 25° C. before the addition of 10 μl of D-luciferin-luciferase reagent. The ATP produced was measured as RLU on a plate luminometer.
Expression and Purification of Recombinant Adenylate Kinases
Clones expressing representative thermostable AKs were secured and recombinant thermostable AKs from the thermoacidophilic archaeon Sulfolobus acidocaldarius and the thermophilic bacterium, Bacillus stearothermophilus produced. The plasmids were transformed into E. coli and the cell extracts shown to contain protein bands on electrophoresis corresponding to the expected molecular masses of the AKs. Thermostable AK activity was measured after incubation at the appropriate temperature (80° C. for the Sulfolobus acidocaldarius AK and 60° C. for the Bacillus stearothermophilus AK).
Purification methods for both thermostable AKs were established and included an initial heat treatment of incubation for 20 minutes at 80° C., to inactivate and aggregate proteins derived from E. coli, followed by affinity chromatography and gel filtration. The affinity chromatography involved adsorption of the enzyme to Blue Sepharose, followed by specific elution with a low concentration of AK co-factors (AMP+ATP and magnesium ions). The ATP and AMP (Sigma) in the elution buffer were degraded by incubation with mesophile apyrase, which is readily inactivated by subsequent heat treatment. Gel filtration chromatography was scaled up to utilise a preparation grade Superdex column to enable large quantities of both enzymes to be prepared.
Primers were designed for PCR amplification of the AK genes from the thermophilic organisms identified during the screening of candidate native enzymes.
The thermostable microorganisms were grown using individually defined growth conditions and genomic DNA isolated and used as templates for PCR amplification of the adenylate kinase genes from each organism. PCR amplified adenylate kinase genes from the thermophilic organisms, Thermotoga maritima, Aeropyrum pernix, Sulfolobus acidocaldarius and Sulfolobus solfataricus were sub-cloned into the vector, pET28a and transformed into a codon enhanced E. coli strain expressing rare tRNAs (Zdanovsky et al., 2000). This E. coli strain is suitable for enhancing expression levels of AT-rich genes.
The success of the transformation was assessed by a mini-expression study, and the results analysed by SDS-PAGE of the culture supernatants before and after induction with IPTG. SDS-PAGE was also used to analyse the supernatants after inclusion of a heat treatment step, which consisted of heating the sample to 80° C. for 20 minutes prior to running on the SDS-PAGE gel to remove heat labile proteins present in the sample.
Sequences:
Analysis of the Thermostability of Recombinant Adenylate Kinases
The thermal stability of recombinant tAK enzymes was assessed in crude E. coli cell lysates.
Cells were grown essentially as described in Example 3 and lysed by sonication. The AK activity of the crude extract was determined both before and after heat treatment at 80° C. for 30 minutes followed by 10-fold serial dilution
The results (see
Genetic Modification of Adenylate Kinases to Improve Stability
Site-directed mutants were constructed in the AK gene from P. furiosus, P. horikoshii and S. acidocaldarius as shown in Examples 6-8 and SEQ ID NOS:17-19 respectively, using standard methods known to those familiar with the art.
In addition to specific changes identified in each gene, the regions underlined in the S. acidocaldarius sequence form the core packing region of the archaeal adenylate kinase trimer structure. Hence amino acid substitutions that disturb the packing of this region are likely to have a major effect in decreasing the thermal and physical stability of the enzyme. Conversely amino acid substitutions that improve the core packing, in particular hydrophobic residues with large side chains, may stabilise the enzyme to heat or other processes. Therefore in addition to the specific mutations already described a number of “selective” approaches were used with localised gene shuffling of related gene sequences in these regions (essentially as described in Stemmer (1994) Nature 370:389-391 and Crameri et al. (1996) Nature Biotech. 14:315-319) and random PCR-based mutagenesis using degenerate oligonucleotides or modified nucleotide mixes (e.g., Vartanian et al. (1996) Nucleic Acid Res. 24:2627-2633). A number of these modifications show altered stability when assessed by recombinant expression in E. coli and rapid assay of adenylate kinase activity in lysed cells at high temperature.
Adenylate Kinases from Pyrococcus furiosus Genetically Engineered to Provide Improved Stability (SEQ ID NO. 17)
Mutations at one or more or all of the sites indicated modify the thermostability of the enzyme. In addition to the three defined changes highlighted, modification of the alanine at position 157 to another small hydrophobic residue (such as I, L) or larger hydrophobic residue (such as F) increases the thermostability of the recombinant protein. Hence, there are 35 variants possible through combination of modifications at these sites. Modification of amino acid 157 to a polar residue such as the T (as observed at the equivalent position in AdkA of P. horikoshii), S Y, D, E, K, R results in a decrease in stability.
Adenylate Kinases from Pyrococcus horikoshii Genetically Engineered to Provide Improved Stability (SEQ ID NO. 18)
The modification of either or both of the residues shown in bold and underlined increases the thermal stability of the enzyme (3 variants are possible).
Adenylate Kinase from Sulfolobus acidocaldarius Genetically Engineered to Provide Improved Stability (SEQ ID NO. 19).
The modification of the underlined residues shown can increase the thermal stability of the enzyme.
Expression of Acetate and Pyruvate Kinases
Following the methods of Example 3, we expressed acetate and pyruvate kinases:
Preparation of a Fibrin-Based Indicator Device
Preparation of tAK Fusions for Cross-Linking to Fibrin.
A transglutaminase substrate sequence (MNQEQVSPLGG—SEQ ID NO:33) is added on to the N-terminus, the C-terminus, or both N- and C-termini, of the thermostable adenylate kinase from S. acidocaldarius encoded by a codon optimised gene clone. (The transglutaminase substrate sequence is interchangeably referred to in these Examples as fibrin, the fibrin peptide or the transglutaminase substrate). This construct is transferred as an NdeI-SalI fragment into an in-house expression vector (pMTL 1015; as described in WO 2005/123764). The expression construct is confirmed by DNA sequencing and transferred into expressions hosts BL21 or RV308 for subsequent expression.
Similarly, the resynthesised tAK gene from Thermatoga maritima (SEQ ID NO:29) is fused to the transglutaminase sequence in the three orientations identified above. The cloning and preparation of the expression system is also as described above.
The fusion constructs can also be expressed in other expression vector-host combinations with the addition of affinity tags for subsequent purification. Particularly useful in this context are expression vectors which add 6-histidine tags on either the N- or C-terminus of the fusion proteins, modifications which aid purification and detection but do not interfere with the intrinsic properties of the fusion proteins. Vectors for this type of modification include pET series vectors (Novagen/Merck) and pQE series vectors (Qiagen).
To generate material for the indicator devices the expression strains are grown initially in 8-liter fermenters essentially under static culture conditions. In brief, the strains are prepared as seed stocks and subsequently diluted into the 8-liters of growth media (modified terrific broth containing additional glucose). The cultures are grown under standard fermentation conditions until the cultures reached an optical density (OD at 600 nm) demonstrating that they are entering stationary conditions (typically at around an OD=5). The fermenters are then held under minimally aerated conditions for up to 12 hours prior to harvesting of material by continual centrifugation.
Purification of tAK Fusions.
The harvested material is then purified according to the following protocol.
Buffer A: 20 mM Tris-HCl; 900 mM NaCl, pH 7.5
Wash Buffer: 20 mM Tris-HCl; 200 mM NaCl, pH 7.5
Buffer B: 20 mM Tris-HCl; 200 mM NaCl, pH 7.5; 10 mM ATP; 10 mM AMP; 10 mM MgCl2
MgAc buffer: 15 mM MgAc (1M Fluka BioChemika), pH 6.8
Optionally, additional protein purification methods are applied to yield a higher purity product. Ion exchange chromatography on either SP-Sepharose Fast Flow or Q-Sepharose Fast Flow resins is particularly effective.
The samples are then analysed using a standard assay format to identify fractions containing peak adenylate kinase activity. This is confirmed by SDS-PAGE analysis using standard techniques (see
The fractions with peak kinase activity are then dialysed extensively against phosphate buffered saline (PBS pH 7.4) and stored until required. Confirmation of the presence of the added transglutaminase substrate sequence (i.e. the fibrin peptide) on the purified tAK is confirmed by SELDI mass spectroscopy analysis (see
Optionally a fusion can be prepared between tAK and the full length fibrinogen molecule to provide further means to incorporate the enzymatic activity within the fibrin film.
Deposition of tAK Fusions onto a Solid Support.
The tAK-fibrin fusion is diluted to around 200 μg/ml in either PBS or bicarbonate buffer (pH 9.6) and applied to a solid support of 316L grade stainless steel, plastic, glass or textiles. The protein is allowed to adhere to the surface for up to 2 hours at room temperature or overnight at 4° C.
Optionally, additional carrier molecules are added at this stage, e.g., sucrose at concentrations up to 1% w/v, albumin at up 1 mg/ml, pig mucin at up to 0.5% w/v. The addition of such carriers may be particularly important for certain types of indicator but the presence of the carrier should not interfere with subsequent interaction and cross-linking to the fibrin film applied in the next stage.
Overlay of Fibrin-Containing Soil and Cross-Linking to Fibrin-tAK Fusion.
A test soil (biological matrix) is then overlaid onto the tAK-fibrin fusion preparation adhered onto the surface as described above.
A solution containing fibrinogen is added to effect the cross-linking of the indicator to the fibrin-containing test soil.
A solution containing up to 3 mg/ml fibrinogen (containing Factor XIII), 2.5 mM CaCl2, and thrombin (up to 5 NIH units per ml) is mixed freshly and added to the coated surface of the solid support. The reaction is allowed to proceed at room temperature for up to 30 minutes, depending on the level of cross-linking required. Optionally, albumin (up to 80 mg/ml) and haemoglobin (up to 80 mg/ml) are added at this stage to provide a tougher and more realistic challenge for cleaning of a blood-like soil. After cross-linking, residual liquid is removed, and the indicator device is left to dry.
Optionally, the tAK-fibrin peptide fusion is added to the fibrin-containing test soil solution (biological matrix) prior its addition to the solid support surface. Cross-linking of the fibrin peptide to the matrix can be increased by adding more Factor XIII and/or extending the duration of the reaction. Cross-linking can also be enhanced by the use of the tAK fusion protein with fibrin peptides added to both ends of the molecule.
Optionally a fibrinogen-tAK fusion could be added directly to this solution to provide further cross linkage of the indicator.
Covalent Chemical Cross-Linking of tAK to Fibrin or Fibrinogen.
The preparation of tAK-fibrin as a fusion protein has already been described above. However, tAK-fibrin may also be prepared by chemically joining tAK to fibrin, fibrin peptides or fibrinogen by a wide range of methods familiar to those working in the field. For example purified protein preparations for fibrinogen or fibrin are obtained from commercial sources (e.g., Sigma). The tAK from S. acidocaldarius is prepared as described above. The tAK is derivatised using the amide reactive reagent SPDP (SPDP (N-Succinimidyl 3-(2-pyridyldithio)-propionate; Pierce chemical company) according to the maufacturer's instructions. The fibrin or fibrinogen is also derivatised using the same protocol. The derivatised tAK is reduced by reaction with mercaptoethanol to yield a reactive sulfhydryl group. This is then mixed with the SPDP-derivatised fibrin causing the formation of covalent bonds between the two molecules. The concentrations of the reaction partners should be determined empirically following the guidelines within the manufacturer's instructions for SPDP.
The chemically linked tAK-fibrin or fibrinogen can be used interchangeably or in addition to the fusion protein throughout the preceding description of this and subsequent examples.
Uses of Fibrin-tAK Indicators
Use in a Washer Disinfector.
An indicator is prepared as described in Example 10. The solid support is a rectangular stainless steel strip 55 mm×5 mm×0.75 mm, which may be coated on one or both surfaces. One or several indicator strips are positioned within the chamber of the washer disinfector. Optimally, these may be positioned in sites which may be the most difficult to clean, providing the highest degree of certainty that the wash process has been effective. Alternatively, they may be positioned to monitor the function of multiple spray arms (i.e. where these may be independent of each other). The indicator strips are clipped to the shelves or other substructure of the washer-disinfector chamber to ensure that they do not move during the wash treatment. The orientation of the surrogate devices can be modified to provide further information about the efficacy of the wash process, for example by positioning them so that the coated surface are at right angles to the direction of water spray.
The instrument load is added and the standard run cycle performed. At the end of the run the devices are removed from the chamber and the presence of residual tAK-fusion assessed, as outlined in Example 12, prior to the removal of the instruments and any subsequent processing. Optionally, devices can be removed during the wash process either by interrupting the process at carefully defined points or by using a machine that provides a method of withdrawing the indicator during the run.
Use in Endoscope Test Procedure.
The indicator device for monitoring an endoscope reprocessing system is essentially similar to that outlined above. A similar size indicator surface, representative of either the stainless steel components within an endoscope, the PTFE tubing or other relevant materials is placed within a tubular chamber. This is attached, via suitable screw, push or bayonet fittings to either the front end of the endoscope or the end which makes contact with patient tissues. This is placed within the endoscope reprocessing unit and the ends of the endoscope tubing and indicator device are coupled to the ports in the unit. The process is run as standard and the indicator device removed at the end of the run for analysis, prior to onward processing or the return of the endoscope to use.
Means of Assessing Cleaning Performance
The indicator device is removed at the end of the test process. The indicator is inserted into a hygiene monitor or luminometer reagent tube and processed according to the manufacturer's instructions, with the indicator device replacing the swab. The hand-held hygiene monitor provides a read-out in relative light units (RLUs) which is directly proportional to the concentration of ATP generated by the tAK-enzyme attached to the biological component. This in turn is directly proportional to the concentration of enzyme over the concentration range typically used for the indicator. The indicator devices are calibrated such that an RLU value below a pre-determined threshold value is indicative of at least a 3-log reduction (or potentially higher depending on the acceptance criteria) in the concentration of the tAK fusion which remains attached to the indicator surface. The batch release of processed instruments is based upon a reduction in the RLU value generated by the residual tAK fusion on the indicator device. This can be identified by either training operatives to return all batches of instruments above the threshold value or by calibrating the hygiene monitor to provide a simple pass or fail read-out based on the RLU value.
The practical process for allowing onward processing of batches of surgical instruments or other processed products is as follows:
This is an example of a suitable protocol, but a number of different reagent tubes or instruments (such as those prepared by BioTrace, Charm or other companies) would be suitable to enable such instrument release protocols.
Preparation of tAK-Sup35 Fusion.
Clones containing the N-terminal domain of Sup35 from Saccharomyces cerevisae fused to either the N- or C-terminus, or both termini, of adenylate kinases from either S. acidocaldarius or T. maraima are generated by standard DNA manipulation techniques. All clones are transferred as NdeI-SalI fragments into the pMTL1015 expression vector and their sequences verified. The expression constructs are used to transform BL21 or RV308 expression strains and the material grown in large scale fermentation conditions, but with minimal aeration.
Expression and purification of a tAK-Sup35 fusion is essentially the same as for the fibrin-peptide fusions described in Example 10, except that the use of the thermal denaturation step (Step 4) is not part of the purification protocol. In brief, cell paste from the fermenter is resuspended in buffer A, and lysed by sonication. The cell debris is removed (no heat treatment is used standardly for these type of fusions) and the supernatant used for column purification as outlined in Example 10.
Under certain growth conditions the fusion proteins may be insoluble, being apparent as inclusion bodies within the cells. In this case the cell pellets are prepared and lysed in the same way, but the resulting insoluble fraction, containing the inclusion bodies, is collected by centrifugation. This material is washed in a buffer (e.g., PBS) containing Triton X100 (up to concentrations of 5%). After each wash the pellet containing the fusion proteins is separated by centrifugation. After 5 washes the inclusion bodies are resolubilised in PBS containing 8M urea and agitated gently for up to 30 minutes. Any residual insoluble material is removed by centrifugation. The urea-solubilised material is dialysed against up to 5×10 volumes of PBS to remove the urea and allow the fusion proteins to refold. Optionally the urea may be removed more rapidly by spraying the urea-solubilised preparation through a fine gauge needle into 100 volumes of rapidly stirred PBS or buffer A as used for purification. The material is allowed to stand at room temperature with stirring for up to 30 minutes prior to subsequent processing.
Subsequent purification of the fusions is carried out essentially as described in Example 10. The supernatant from either lysed cells or solubilised and refolded inclusion bodies is loaded onto a pre-equilibrated Blue Sepharose Fast Flow column. After extensive washing in buffer A and subsequently in wash buffer, the protein is eluted using buffer B. Peak fractions are determined by SDS-PAGE analysis and enzyme assay. Fractions are then pooled and dialysed into PBS.
Conversion of tAK-Sup35 to an Amyloid Form.
The Sup35-tAK fusions when assembled into fibrils are more representative of amyloid proteins such as prions which are key molecules against which to assess the efficacy of decontamination processes.
The amyloid form of the Sup35-tAK fusions is generated by either refolding of the purified soluble protein or by modifying the conditions used for dialysis of the urea-resolubilised inclusion body preparations. In the first case, a conformational change is induced by exposure of the fusion proteins to conditions around pH 4 (e.g by dialysis into a suitably buffered solution at pH 7.4 optionally containing up to 1M NaCl). In the latter case, the resolubilised fusion proteins in 8M urea/PBS are dialysed for 6-12 hours at room temperature against 2M urea, 300 mM NaCl, in PBS (pH 7.4). Alternatively, the fibrilisation can be induced by dialysis against 20 mM Tris pH8.0 10 mM EDTA under similar incubation conditions. Electron microscopy is used to confirm the presence of fibrils (see
Optionally, the fusion proteins may be incorporated into fibrils containing normal Sup35. This is achieved by mixing the fusions with unfused Sup35 expressed in the same way, at ratios between 1:1 to 1:10 fusion:Sup35.
Deposition of tAK-Sup35 Fusions onto Solid Support.
Deposition of the fibrils onto a solid support is effected by simple protein adsorption in a suitable buffer (e.g., PBS pH 7.4 Bicarbonate buffer pH 9.6) in the presence of high levels of NaCl. The use of charged or precoated surfaces (e.g., plastics coated with Poly-L-lysine) is useful in providing surfaces which can more effectively bind the fusion proteins.
Optionally, the fibrils may be deposited in a suitable carrier, such as sucrose (to 1%), pig mucin (up to 0.5%), or albumin (up to 1 mg/ml).
Overlay of Test Soil
A test soil (biological matrix) is then overlaid onto the amyloid preparation adhered onto the surface as described above.
Suitable biological matrices in which the amyloid indicator is embedded include e.g., 0.5% mucin, with or without albumin, a commercial test soil (such as that manufactured by Browne's) or any one of the test soils identified in guidance documents issues by national and international standards committees (e.g., Edinburgh soil as detailed in HTM 01/01 (UK).
Assembly of Amyloid Fibrils within the Test Soil
Given the ability of amyloids to self-assemble in complex matrices it is possible for the amyloid-tAK fusion to be mixed with soil components prior to fibril formation and subsequent deposit onto surfaces. This provides further options for indicators in which the amyloid fibrils may be mixed and inter-chelated with other soil components providing a different type of matrix that may be harder to remove from surfaces.
Uses of tAK-Sup35 Indicator
Use of tAK-Sup35 Indicator for Assessing Prion Removal from Surfaces in a Washing Process.
An indicator as described in Example 13 is prepared as fibrils and dried down onto a steel surface in the presence of 0.5% mucin. The indicator is placed within the chamber of a washer disinfector at pre-determined locations. The instrument load is added. The process is started as per the manufacturer's instructions and any process records completed. At the end of the process, and before any instruments are taken from the machine, the indicator devices are removed and assessed as described in Example 12.
Use of tAK-Sup35 Indicator for Assessing Prion Inactivation in a Protease-Based Process.
Indicators as described in Example 13 are prepared as fibrils with a high ratio of free Sup35:Sup35-tAK (in excess of 5:1) and deposited onto solid support strips in the presence of Edinburgh soil. The indicator devices are inserted into a pre-soak bath containing freshly made PRIONZYME™ (Genencor International) prion inactivation treatment (at 60° C., pH 12). The indicator strips are clipped to the side of the bath such that the ends of the indicators are within the bulk of the liquid. Instruments are added as required and processed for 30 minutes. The indicator devices are removed from the bath at the end of the process, prior to removal of the instruments and assessed as described in Example 12.
Use of tAK-Sup35 Indicator for an Oxidative Process Aimed at Destroying Prions.
An indicator as described in Example 13 is prepared as fibrils using only Sup35-tAK, and deposited onto a stainless steel surface (optionally in the presence of 0.1% w/v sucrose). The indicator is attached to the inside of the lid of a GENESIS™ container in which the instruments are prepared for processing and the lid closed. The container is inserted into the load chamber of a suitable processor for oxidative challenge (e.g., the 125 L ozone steriliser; TSO3 or a vapour phase hydrogen peroxide technology such as that described in published papers by Fichet et al. 2004; Lancet) and the process run according to manufacturers' instructions. At the end of the process, the GENESIS™ container is taken out of the chamber and the indicator devices are removed and processed as described in Example 12.
Preparation of a Neurological Soil with tAK-Coupled Components
Identification of Components Essential for a Neurological Test Soil.
The critical target components encountered with neurosurgical processes that may remain attached to surgical instrument surfaces can be determined in experimental studies. Surgical instruments from neurosurgical wards may be treated in routine cleaning processes. Residual protein or other biological molecules can be solubilised from the surface of the instrument using partial acid hydrolysis, strong alkaline cleaners or the use of suitable lytic enzymes (e.g., proteases, nucleases, lipases). The principle molecules can then be determined using mass spectrometry techniques such as Surface-enhanced laser desorption ionisation (SELDI) or equivalents.
The same analysis may be achieved by artificially soiling surgical instruments with human neurological material or equivalent samples from animal species (e.g., rodent brain homogenate).
A representative neurological test soil will require a variety of components that include, inter alia, nerve derived proteins (e.g., neurofilament), lipids or glycolipids representative of neuronal environments (e.g., sialic-rich gangliosides) and carbohydrates. If the test soil is designed to address particular issues regarding specific diseases, such as diseases caused by protein aggregation (e.g., prion disease, Alzheimer's disease) then these components, or surrogates thereof, will also be valuable additions to the test soil.
Cross-Linking of tAK-Fusions to Protein or Glycolipid.
A recombinant tAK fusion can be made to neurofilament proteins or sub-domains thereof by using the methods essentially as described in Examples 10 and 13.
In addition, cross-linking can be achieved without the need to generate recombinant expression clones. This may be particularly useful where heavily glycosylated proteins or glycolipids are linked to the tAK. In this case the protein or glycolipid is purified either from a suitable source or generated by expressing a suitable gene construct in a eukaryotic cell line (e.g., mammalian cell, baculovirus expression system). Purification may be via one of a variety of well known protein purification methods or by detergent solubilisation of membrane lipids. The purified material is then cross-linked to purified tAK using one of a wide range of coupling chemistries (e.g., SPDP (Pierce chemicals) used to link proteins via primary amines on proteins; treatment with meta-periodate used to open up carbohydrate groups allowing cross linking to glycolipids). Further suitable methods for effecting cross-linking of the tAK with carbohydrate or lipid-containing molecules are described in detail in Example 23
Of particular use in this application is the covalent coupling of the tAK to biological components such as gangliosides, including those specific for neuronal cells (e.g., GT1b, GT1a) and those of general cell origin (e.g., GM1). Gangliosides are purified by standard methods involving detergent solubilisation, phase partitioning and differential centrifugation. Alternatively the indicator can be formulated using commercially available purified gangliosides.
Conjugation of tAK to Nucleic Acid Components of Neurological Test Soil.
The tAK is cross-linked to a suitable nucleic acid, either purified, generated synthetically or amplified from a template using PCR or similar techniques. The cross-linking can be achieved by incorporating a biotin label onto the nucleic acid, e.g., during synthesis and using a tAK-cross-linked to streptavidin.
Deposition of Test Soil Components onto Solid Support.
The deposition of one or more tAK indicators onto a solid support can be achieved as described in Examples 10 & 13. In brief, the tAK complexes are prepared in PBS or bicarbonate buffer (pH 9.6) and allowed to dry on a polycarbonate surface for 30 minutes at room temperature. Optionally, sucrose may be added up to concentrations of 1% w/v. The binding conditions are designed to favour attachment via the biological component rather than the tAK, for example by blocking remaining active groups on the surface of the tAK using a suitable surface modifying agent or by incorporation of high levels of NaCl.
Optionally, the deposited neurological soil may be fixed by treatment with 70% ethanol or isopropanol. To achieve this, the indicator is incubated in 70% isopropanol for 30 minutes at room temperature. This mimics one of the commonly encountered processes which may increase the resistance of contaminating materials on surgical instruments, and therefore provides the indicator with an effective way of monitoring the removal of such materials.
Preparation of Norovirus Capsid Protein (58 kDa)—tAK Fusions
A gene encoding a 58 kDa capsid protein from norovirus is generated as a synthetic construct. This clone is cloned onto the 5′ end of the gene encoding the thermostable adenylate kinase from Thermotoga maritima to generate a single fusion protein. After sequence verification this clone is transferred into either a pMTL vector for expression in E. coli or into a baculovirus expression system (e.g., BacPAK expression system; Clontech) for expression in insect cell lines such as SF9 cells.
Expression and Purification.
Expression of the capsid protein-thermostable kinase fusions in E. coli is carried out essentially as described in the previous examples. The proteins are purified using a similar protocol on Blue Sepharose Fast Flow with no thermal denaturation step applied during the cell lysis protocol. Purified proteins are analysed by SDS-PAGE analysis and by enzymatic assay as described in the previous examples. The assembly of the fusion proteins into virus-like particles (VLPs) is promoted by altering the pH and salt concentration.
Baculovirus expression and subsequent purification is carried out essentially as described in Jiang et al., (1992) “Expression, self-assembly and antigenicity of the norwalk virus capsid protein”, J Virology, 66, page 6527-6352.
Deposition on Solid Supports.
The purified VLP-tAKs are deposited onto a solid support suitable for validating clean-down and disinfection of surfaces used in food preparation or following outbreaks of norovirus in hospital settings.
For validating the decontamination of food preparation surfaces, VLP-tAKs are prepared in a PBS buffer containing a crude food extract comprising egg albumin and sucrose. This matrix is coated onto a polyvinyl strip measuring 5 cm×5 cm and allowed to dry for either 2 hours at room temperature or overnight at 4° C.
For assessing the decontamination of a healthcare facility potentially contaminated following an outbreak of norovirus, the VLP-thermostable kinase indicators are made up in a preparation designed to mimic healthcare-related soiling. This included various blood-related proteins as described above, or one of the standard bed-pan soils enshrined in national and international decontamination standards. Particularly efficacious indicators are set up using textile solid supports representative of, for example, hospital curtains or gowns.
Use of Norovirus VLP-tAK Fusions for Validation of Viral Removal Processes.
The norovirus VLP-tAK fusions are particularly advantageous for validating the ability of processes to remove norovirus from water or food samples. They retain the size, charge and hydrophobicity properties of the parent virus and as such will mimic their behaviour in removal processes. This is particularly useful in this case as no culture method exists for norovirus and as such it is currently not possible to measure live virus clearance other than by RT-PCR, a potentially time consuming method.
For example, the norovirus VLP-tAK fusions are put into a water source and filtered through a process designed to remove viral particles. Sufficient viruses are input to measure the required level of viral clearance. The numbers of VLPs post filtration are measured and assessed against the pre-determined pass/fail criteria.
Generation of Bacteriophage MS2 Coat Protein—tAK Fusions
The generation of MS2 coat proteins and their spontaneous assembly into virus like particles has been described in a number of studies, for example in Peabody (2003), “A viral platform for chemical modification and multivalent display”, J Nanobiotechnology, vol 1, page 5.
The protein sequence of MS2 coat protein capable of generating VLP when expressed in E. coli is given below (SEQ ID NO:62):
Constructs of MS2 coat proteins are generated with the tAK from Thermatoga maritima, fused at either the N- or C-terminus of the expressed protein. Depending on the location of the fusion this results in the incorporation of the tAK either within the lumen of the VLP or exposed on the surface. The two locations both have useful properties for their application as indicators. Optionally the MS2 coat protein may be modified by inclusion of a cysteine residue at position 15 in the native sequence (substitution threonine15 to cysteine). The VLP-tAK fusions are purified using a combination of the methods described for tAK fusions above (Examples 10 and 13) with additional ion exchange steps if required. The intact VLPs incorporating the tAK can also be purified on the basis of size exclusion using a Sepharose CL-4B column.
Alternatively, purified tAK can be cross-linked to MS2 VLPs using chemical cross-linking reagents. In brief, tAK from S. acidocaldarius is derivatised with SPDP and reduced to yield a reactive sulfhydryl group. This is then mixed with the MS2 VLPs containing the T15C variant of the protein. This effects covalent disulfide bonds between the two partners. These types of covalently linked molecules can be used interchangeably with the genetic fusions throughout the remainder of these examples.
Deposition of MS2 Coat Protein—tAK Fusions on Solid Supports.
The purified tAK-containing MS2-VLPs are deposited on surfaces in a similar way to the fusions described in the previous examples using standard protein adsorption techniques. Optionally, highly charged or hydrophobic surfaces may be used to provide an indication of viral removal from specific surfaces within process regimes.
The VLP-tAK fusion may be deposited alone or may be contained within a suitable soil matrix designed to represent the relevant soiling encountered during the treatment process to be validated. For example, a bed-pan soil may be used for evaluation or validation of the removal of faecal material from either bed-pans, toilets or during diarrhoeal episodes.
Use of MS2-tAK Fusions for Validating a Cleaning Regime.
The MS2-VLP indicator is set up on a ceramic surface as described above. The ceramic indicator is exposed to the same cleaning chemistry as the bathroom surfaces to be cleaned, e.g., to diluted sodium hypochlorite at a dilution of approximately 2.5% (v:v), and under the same conditions (30 minutes at ambient temperature). At the end of the process the ceramic indicator is inserted into a hygiene monitor tube and the residual MS2-tAK measured using the method of Example 12. If cleaned below a pre-set threshold then the cleaning regime is deemed to have been successful. If not then repeat cleaning is required to minimise any risk of disease transmission.
Use of MS2-tAK Fusions for Validating a Viral Removal Process.
As the MS2-tAK VLPs mimic the size, surface charge and hydrophobicity of the parent virus and are capable of representing a wide variety of related viruses (e.g., polio virus), these indicators are extremely useful for validating viral removal processes in either a laboratory or field setting. The rapidity of the tAK assay provides significant advantages over traditional culture-based methods.
For example, a water treatment system may be validated in situ using the MS2-tAK VLPs. Sufficient MS2-tAK VLPs are put into the input water in the treatment plant to provide a sufficient log clearance estimation for the efficacy of the process, as determined by national or local regulations. For example, 109 VLP-tAKs per liter are put into the input water. The process is performed and approximately 1 ml samples of the post-process water is tested in a suitable hygiene monitor tube system (e.g., AQUA-TRACE™, Biotrace UK). A value indicating less than 1 VLP-tAK per ml of water would be sufficient to demonstrate a 6-log clearance of viruses by the process employed. This could be done within 2 minutes of the process being completed rather than 16-24 hours that would be required for a standard culture-based method in E. coli.
Such methods are relevant for validating a wide range of viral inactivation processes used widely in the healthcare, food, water or pharmaceutical industries. In the vast majority of cases it can replace the use of the parent MS2 bacteriophage, used widely to validate viral-removal processes, providing far more rapid and sensitive determination of removal. For example, water purification through ceramic microfilters (replacing the parent bacteriophage in Wegmann et al., 2007, “Modification of ceramic microfilters with colloidal zirconia to promote the adsorption of viruses from water”), treatment of water with gaseous chlorine (Clevenger et al., 2007, “Comparison of the inactivation of Bacillus subtilis spores and MS2 bacteriophage by MIOX, ClorTec and hypochlorite”, J Applied Microbiology, 103, p 2285-2290), validation of virucidal efficacy of hand washing (Jones et al., 1991, “The use of bacteriophage MS2 as a model system to evaluate virucidal hand disinfectants”, J Hospital Infection, 17, p 279-285). Other examples would be to validate, in process, the removal of virus particles from fractionated blood, cellular extract of human or animal origin, pharmaceutical products, food preparation (e.g., shell-fish extracts).
Preparation of Further Kinase-VLP Fusions Suitable for Evaluating and Validating Viral Removal or Destruction
The table below lists a series of VLP fusion proteins that are valuable in the development of indicators for assessing removal or inactivation of a range of viral pathogens. These represent either actual pathogens where the validation of removal may be essential, or model viruses capable of representing the removal of a range of related pathogens. The pathogens are from both the medical and veterinary field, and also encompass a range of known or possible zoonotic pathogens which may transmit from animals to humans.
E. coli (pET3d
Journal of
Nanobiotechnology, 1, p5
Methods, 40, p60-65
Virology, 333, p239-250
The protein sequence of bacteriophage PP7 coat protein monomer and dimer (Caldeira and Peabody, 2007, Journal of Nanobiotechnology, 5, p 10) is given below. Thermostable kinase genes may be fused to the C-terminus of either the monomer or dimer.
Expression of Kinase—Bacterial Fimbriae Fusions for Use in Development of Indicators to Assess Biofilm Removal from Surfaces
A fusion between the tAK from Thermotoga maritima and the CsgA protein from E. coli is generated by standard recombinant cloning familiar to those with knowledge of the art. The protein sequence generated is shown below.
MKLLKVAAIAAIVFSGSALAGVVPQYGGGGNHGGGGNNSGPNSELNIYQY
GGGNSALALQTDARNSDLTITQHGGGNGADVGQGSDDSSIDLTQRGFGNS
ATLDQWNGKNSEMTVKQFGGGNGAAVDQTASNSSVNVTQVGFGNNATAHQ
Y
maritima fused to the N- terminus of the CsgA
For expression the clone is transferred to a suitable expression vector such as pET 32a (Novagen) or pMAL-C2x (New England Biolabs) and the protein expressed in a suitable host strain (e.g., BL21) under normal growth conditions.
Depending on the growth conditions the thermostable kinase-CsgA fusion may be expressed either solubly within the cytoplasm of the cells or as an insoluble inclusion body within the cell. In the former case purification is carried out as described in Examples 10 and 13. In the latter, inclusion bodies are isolated by centrifugation following cell lysis and washed extensively in buffer containing 1% Triton X100. Inclusion bodies are solubilised by suspension in 8M Urea or 6 M guanidine hydrochloride and then refolded by rapid dialysis in very low salt buffer (typically less than 20 mM NaCl).
The generation of self assembled layers is mediated by incubating the purified and enzymatically active fusion protein with a hydrophobic surface (e.g., Teflon) in 10 mM Tris pH8. For hydrophilic surfaces such as stainless steel or glass the fusion is incubated in 50 mM Sodium acetate buffer pH4, optionally in the presence of 0.1& Tween 20. Elevated temperatures up to 80° C. may be used to enhance binding or to ensure uniform coverage of surfaces.
Fusions with the equivalent protein sequences from other Gram-positive of Gram-negative organisms (e.g., AgfA from Salmonella species) can also be used.
MKLLKVAAFAAIVVSGSALAGVVPQWGGGGNHNGGGNSSGPDSTLSIYQY
GSANAALALQSDARKSETTITQSGYGNGADVGQGADNSTIELTQNGFRNN
ATIDQWNAKNSDITVGQYGGNNAALVNQTASDSSVMVRQVGFGNNATANQ
Y
Further Self-Assembling Peptides and Proteins for Generation of Biofilms
The generation of further indicator devices containing tAK fusions with peptides capable of self-assembling into fibrils, or surface reactive biofilms is also provided. A list of suitable fusion partners is shown in the table below.
E. coli, yeast
Physiol Biochem
Pharmacol, 159, p1-77
E. coli, yeast
Acad Sci USA, 101,
E. coli, yeast;
E. coli, yeast
FEBS J., 274, p4336-4346;
Megabalanus rosa;
Biomacromolecules, 8,
E. coli, yeast,
Biol Chem, 278, p2444
E. coli, yeast
E. coli, yeast
E. coli, yeast
E. coli
Nat Rev Microbiol, 3,
E. coli
Physiol Biochem
Pharmacol, 159, p1-77
E. coli
Microbiol. On line
Microbiol.
E. coli or
E. coli, yeast
pastoris
Micron e-pub
Schizophyllum
commune, RodA/B
fumigatus)
E. coli, yeast
pastoris
E. coli,
Clostridia
Mol Micro., 63, p629-643
Clostridium
taeniosporum)
Indicators for Monitoring Efficacy of Contact Lens Cleaning for Removal of Biofilms
A range of bacteria and viruses pose a potential risk to contact lens wearers both in planktonic and biofilm forms. Indicator devices can be advantageously generated to monitor the effectiveness of cleaning methods for the removal of such organisms.
The fimbriae fusions described above have can provide an indication of the removal of Gram-negative pathogens. Any member of the hydrophobin gene family is a suitable indicator fusion for the removal of fungal pathogens where these highly conserved molecules are the principle mediators of attachment. Hydrophobin genes, or equivalents from Fusarium species and Candida albicans, are suitable as these organisms represent one of the greatest threats for eye infection leading to ulceration and long term damage.
Fusion proteins can be generated with any of these molecules and formulated within suitable films as described in the previous examples. These indicators can be incorporated as part of the wash chamber, in which the re-useable contact lens is to be cleaned. The process is performed for the appropriate length of time and the lens removed. The indicator is removed and the presence of active fusion protein assessed using a hygiene monitor in the usual way. If below the pre-set thresholds the contact lens is suitable for re-use. If above (“failed” then the contact lens must be re-processed or destroyed.
Fusarium species
Fusarium species
Generation of tAK Fusions to Cement-Like Proteins for Use in Determining Biofilm Removal
tAK from Thermotoga maritima is fused to the 19 KDa protein from Balanus albicostatus and expressed as described above. Purification is effected from either the soluble or insoluble fraction. Refolding and subsequent deposition of the tAK-containing film onto a solid support is achieved as in Example 19. The thickness, rate of deposition and subsequent removal of the biofilm can be altered by modifying both the salt concentration and pH and by altering the concentration of the fusion protein.
Protein sequences of barnacle cement-like proteins suitable for use in the invention are described below. The thermostable kinase may be fused to either the N-terminus or C-terminus of the cement proteins.
albicostatus with the tAK from Thermotoga maritima; N-terminal fusion
albicostatus with the tAK from Thermotoga maritima; C-terminal fusion
Protein sequence of a novel barnacle cement proteins for use in the generation of thermostable kinase fusion proteins. The calcite dependent aggregation and adherence of this protein enable this type of indicator to monitor processes capable of removing mineral ions from aggregates in such a way as to destabilize and remove biofouling or biofilms. The thermostable kinase may optionally be fused to the N-terminus or C-terminus. Sequence from Mori et al., 2007, Calcite-specific coupling protein in barnacle underwater cement; FEBS J, 274, p 6436-6446. Protein sequence of
Balanus albicostatus calcite-specific adsorbent
Peptide sequence of a peptide derived from a barnacle cement protein for use in the formation of thermostable kinase-containing peptide biofilm preparations. Sequences derived from Nakano et al., 2007, “Self assembling peptide inspired by a barnacle underwater adhesive protein”; Biomacromolecules, vol 8, p 1830-1835.
Use of the Cement—tAK Fusion for Monitoring Cleaning of Medical Devices
The indicator described above is deposited onto stainless steel of a grade representative of surgical instruments using the deposition methods described in the previous examples. The device is inserted into a standard instrument load and the process performed as standard. The device is removed at the end of the process and the residual activity of the tAK fusion is correlated with removal of potentially infectious soil components.
Use of the Cement—tAK Fusion for Monitoring Removal of Biofouling.
The indicator described above can also be used to monitor the removal of biofouling in other contexts. For example the indicator may be attached to the bottom of a boat being subjected to cleaning for removal of barnacles and other marine biofilms. The indicator is subjected to the same process and assessed at the end of the procedure. Whilst visual removal of material is the key means of determining performance, the use of a more sensitive assay method allows an assessment of the removal of microscopic amounts of soiling which would provide a better primer for the re-establishment of the marine biofilm. Hence in this application the indicator provides both a demonstration of immediate efficacy and an indication of the longevity of the treatment.
Cross Linking of tAK to E. coli or Staphylococcus aureus Exopolysaccaride
The exopolysaccharide is generated by growing the relevant bacterial strain under standard growth conditions in either liquid, semi-liquid, biofilm or solid cultures familiar to those with knowledge of the art. Bacteria, typically towards the end of the logarithmic phase of growth are collected by resuspension (where required) and centrifugation. The cells are washed in low osmotic strength buffers (typically below 100 mM NaCl/NaPO4) usually at near neutral pH. The washing may be carried out by mixing vigorously for 1 hour at room temperature or overnight with gentle agitation at 4° C. Optionally an acidic preparation may be extracted using an acetate buffer at pH between 3 and 5. Limited cell perturbation may be achieved using very low energy sonication or by the addition of low levels of detergent. Preparations may be filter sterilised through a 0.2 μm nitrocellulose or cellulose acetate filter prior to storage at 4° C. or −20° C.
Cross-linking of the polysaccharides to tAKs can be achieved using a variety of coupling chemistries. In the first example the tAK from Sacidocaldarius is used. The coupling uses the heterobifunctional reagent ABH (p-Azidobenzoyl hydrazide; Pierce Chemical company product number 21510). The protocol is as follows.
In a second example of the chemistries available the heterobifunctional agent MPBH (4-[4-N-maleimidiophenyl]butyric acid hydrazide hydrochloride; Pierce Chemical company product 22305)) is used. The brief protocol is as follows:
The methods described above are applicable to generating tAK conjugates with a wide range of complex carbohydrates, glycoprotein, glycolipids and other carbohydrate containing polymers including those from mammalian, bacterial, archaeal, plant or fungal origin.
Use of Indicators Based on Exopolysaccharide-tAK Fusions.
The EPS-tAK indicator is prepared in a suitable coating buffer such as phosphate buffered saline (pH 7.0-7.4), sodium bicarbonate (pH 9.0-9.6) or sodium acetate (pH4.0-5.5), optionally containing up to 500 mM NaCl at a relatively high concentration, e.g., 0.1-2.0 mg/ml. The solution is deposited onto a suitable solid support, such as surgical steel, plastics similar to catheters and lines, plastics used commonly in endoscopes. The interaction is allowed to proceed typically for 1-2 hours at room temperature and the coated surface allowed to dry at room temperature overnight prior to storage.
Optionally other biological matrix components may be added either during the coating phase or subsequent to it.
The indicator is included in the process to be monitored, e.g., within a washer disinfector cycle. The device is removed at the end of the process and inserted into hygiene monitor tubes to provide the read-out of the effective destruction and/or removal. The process is deemed effective if the value obtained is below the pre-determined thresholds of the hygiene monitor of luminometer. If successful the batch of instruments or material processed at the same time as the indicator may be used or passed on for subsequent processing. If deemed a fail the material must be reprocessed with a new indicator device.
Further Examples of Complex Carbohydrates and Glycoconjugate Indicators
A wide range of complex carbohydrate-containing molecules can be incorporated into indicator devices of the invention by covalent attachment to tAKs using methods such as those set out above (Example 23). Some further examples of these are provided in the table below.
Legionella, E. coli,
Staphylococcus species,
Streptococcus species,
Pseudomonas species,
Acinetobactor, Shigella,
Campylobacter, Bacillus
Streptomyces
Candida albicans and
Bacillus species,
Clostridial species; other
Coupling of tAK to Mucus to Validate Processes Designed to Reduce Mucus Contamination of Medical Products
Mucus is purified from a mucus-producing cell line such as normal human bronchial cells, cultured cells or is collected from sputum samples from patients. Washing in water or low salt solutions is sufficient to separate the mucin from most other components. Alternatively, purified mucin of animal origin e.g., porcine mucin, can also be used. The purified preparation is cross-linked to tAK using the methods described above, either to the protein component, through SPDP-coupling of the proteins as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 0803068.6 | Feb 2008 | GB | national |
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| Number | Date | Country | |
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| Parent | 12918628 | US | |
| Child | 15205841 | US |
