Patent Application
20060140911
The present invention concerns compositions for treating bacterial biofilms using bacteriophages, modified bacteriophages, and associated methods and uses of bacteriophages.
There is an urgent need in the near future to develop alternative anti-microbials to replace antibiotics for treating a whole spectrum of bacterial diseases. Action is needed due to an alarming increase of antibiotic resistance that poses a very real threat to modern medicine. Intermittent treatment and the re-emergence of infection tends to create selective pressure towards producing resistant microbial strains, and the nature of hospital environments and the sheer number of routine operations make the spread of infection more hazardous. Additionally, the ease and frequency of international travel assists in the spread of resistant bacteria throughout the world.
Many pathogenic microorganisms reside within biofilms, which biofilms cause additional problems when designing new anti-microbial agents. In this regard, bacteria and fungi growing as a biofilm rather than in free-floating (ie. planktonic) forms tend to be particularly resistant to anti-microbial agents and to be particularly difficult for the host immune system to render an appropriate response.
Examples of biofilm-associated microbial infections include infections of:- oral soft tissues, teeth and dental implants; middle ear; gastrointestinal tract; urogenital tract; airway/lung tissue; eye; urinary tract prostheses; peritoneal membrane and peritoneal dialysis catheters, indwelling catheters for hemodialysis and for chronic administration of chemotherapeutic agents (Hickman catheters); cardiac implants such as pacemakers, prosthetic heart valves, ventricular assist devices, and synthetic vascular grafts and stents; prostheses, internal fixation devices, and percutaneous sutures; and tracheal and ventilator tubing. Both indwelling and subcutaneous biomedical implants or devices are potential sites for microbial infections and represent important targets for the control of infection, inflammation, and the immune response. Biomedical systems such as blood oxygenators, tracheal lavage, dental water units, and dialyzers are also susceptible to bacterial contamination and biofilm formation.
A biofilm is an accumulation of microorganisms embedded in a matrix of polysaccharide. Biofilms may form on solid biological or non-biological surfaces and are medically important, accounting for over 80 percent of microbial infections in the body.
Virulence and pathogenicity of microorganisms is often enhanced when growing as a biofilm, and new strategies are therefore required to control biofilm formation and development. For example, US20002/0037260 describes a system in which an anti-microbial agent (eg. an antibiotic) and a biofilm-degrading enzyme (eg. alginate lyase) are each coupled to anchoring molecules, which help localise and maintain said agent and enzyme at the site of the biofilm where they can exert their effect.
However, biofilms are difficult to treat with anti-microbials and bacterial resistance to antibiotics is enhanced up to 1000-fold over the level observed when grown under planktonic conditions. In addition, biofilms increase the opportunity for gene transfer between bacteria and may be significant for the transfer of resistance genes to associated susceptible bacteria. Gene transfer can convert a previously avirulent strain into a virulent pathogen.
New, and more virulent microbial phenotypes may be expressed when growing within a biofilm.
Bacteria embedded within biofilms are resistant to both immunological and non-specific defence mechanisms of the body. Contact with a solid surface induces the expression of a bacterial enzyme, which catalyses the formation of exo-polysaccharides that promote colonisation and protection.
Immune responses are only directed towards those antigens on the outer surface of the biofilm. Antibodies and other serum or salivary proteins may fail to penetrate into the biofilm. Cells within the biofilm remain hidden from antibody and complement factor recognition, and thus from subsequent white blood cell phagocytosis. The presence of biofilms can modulate cytokine synthesis, and can interrupt production of antibodies via synthesis of superantigens. Phagocytes are unable to effectively engulf a bacterium growing within a complex polysaccharide matrix attached to a solid surface. This may result in phagocytes releasing large amounts of pro-inflammatory enzymes and cytokines, leading to inflammation and destruction of nearby tissues.
As bacterial cell density within a biofilm increases, the bacteria may communicate with each other. This can lead to the secretion of low molecular weight molecules that signal when the population has reached a critical threshold. This process, called quorum sensing, is responsible for the expression of virulence factors. For example, Pseudomonas aeruginosa produces destructive proteases when the number of these bacteria reaches a high enough density in the airway biofilms of cystic fibrosis (CF) patients.
Accordingly, alternative curative and prophylactic approaches for tackling microbial infections within a biofilm are required.
Bacteriophage based therapies have been considered in the past for the treatment of free-floating (ie. planktonic) microbial infections. However, following the discovery of antibiotics, phage therapy was eclipsed in the 1940s, although extensive clinical research continued in Eastern Europe. In Russia and Georgia, phage are currently produced and marketed by a number of companies for the treatment of enteric disorders, bladder infections and post-operative infections.
In Britain and the United States, there has been renewed interest in the application of phage therapy since the 1980s. For example, the successful treatment of domestic animals with E. coli infections has been reported by Smith and Huggins (1983; 1987), and by Barrow et al. (1998). Phage have been used in treating burns infected with P. aeruginosa. Soothill et al (1994) have demonstrated that skin-graft rejection could be prevented in a guinea pig model by prior treatment with Pseudomonas phage, and in an earlier study (Soothill et al 1992) have demonstrated phage mediated protection of mice from a systemic Pseudomonas infection. Biswas et al. (2002) have recently reported the successful bacteriophage mediated rescue of bacteremic mice infected with vancomycin resistant Enterococcus faecium. Bacteriophage have also been used in the past for treatment of plant diseases, such as fireblight as described in U.S. Pat. No. 4,678,750.
However, none of the above art addresses the treatment of biofilm infections, which account for many current clinical infections, and their associated medical conditions (see Table 1).
One of the first studies to examine the interaction of bacteriophage with biofilms was reported by Doolittle et al. (1995, 1996). Biofilms of E. coli strains 3000 XIII developed on the surfaces of polyvinylchloride coupons in a modified Robbins device were infected and lysed using bacteriophage T4D. Similar studies with phage E79 infecting Pseudomonas aeruginosa indicated phage were infecting the surface organisms but access to the cells deep in the biofilm was restricted. Temperature and nutrient concentration did not appear to affect susceptibility, but low temperature and low nutrients did prolong the time for lysis to occur and slowed the spread of infection within the biofilm. The E. coli biofilms were relatively thin (15-30 μm) compared to the P. aeruginosa biofilm (150 μm).
Sutherland et al. (1999) reported that, during the early stages of biofilm development, bacteriophage have an effect on biofilm development. Surface decontamination of stainless steel and polypropylene contaminated with Listeria monocytogenes was evaluated using Listeriaphage. Phage suspensions at concentrations up to 3.5×108 pfu per ml were found to have an effect in reducing the bacterial count, which was comparable with 20 ppm solution of an industrial sterilizing agent (QUATAL), which is a quaternary ammonium compound (Roy et al. 1993). The latter paper also describes sterilization methods employing phage suspensions in combination with QUATAL.
* Abbreviations:
CAPD, continuous ambulatory peritoneal dialysis;
ICU, intensive care unit;
IUD, intrauterine device.
Tait et al (2002) describes another phage-based method for sterilizing work surfaces contaminated by a biofilm. In more detail, the authors describe the use of compositions containing an Enterobacter strain-specific bacteriophage, and compositions containing a polysaccharide deploymerase in combination with a
According to a first aspect, the present invention provides a composition for treating a bacterial biofilm, comprising a bacteriophage, and a first polysaccharide lyase enzyme (eg. an alginate lyase). The first polysaccharide lyase may be absorbed onto the surface of said bacteriophage. The composition may further comprise one or more pharmaceutically-acceptable antimicrobial agents (eg. antibiotics, and/or defensins), a second or more polysaccharide lyases (preferably different from the first), optionally adsorbed onto the surface of the bacteriophage, and/or a DNase.
The bacteriophage may encode said first, second or more polysaccharide lyase, said DNase, and/or said pharmaceutically-acceptable antimicrobial agent. The bacteriophage can penetrate biofilms and infect biofilm-associated bacteria to cause a reduction (eg. by lysis) in bacterial numbers, preferably a reduction of between about 1 and 3 logs of bacterial viable counts. Also provided are modified bacteriophages, methods of creating modified bacteriophages, compositions for treating biofilms comprising bacteriophages, and methods for treating biofilms using the bacteriophages and compositions of the invention.
In the context of the present invention, the term “first polysaccharide lyase” may embrace related enzymes known as polysaccharide depolymerases. Moreover, the “first polysaccharide lyase” of the invention is exogenous with respect to a target bacterium in the targeted biofilm. For example, the “first polysaccharide lyase” is preferably phage-encoded, phage-associated, or present as a discrete component of the composition.
The following advantages are provided by the present invention, which employs the use of a bacteriophage to target and destroy (or protect against the formation of) infectious biofilms.
Phage are self-replicating and self-limiting and may be delivered by aerosol to the lungs. The self-replicating property is an advantage when patient compliance towards regular drug therapy is poor. disinfectant for sterilizing work surfaces in an industrial environment.
Bacteriophage SF153b, isolated from sewage and able to infect the biofilm-forming bacterium Enterobacter agglomerans 53b, was shown to possess a depolymerase specific for the exopolysaccharide of strain 53b (Hughes et al., 1998). Using a Robbins device, the phage was shown to disrupt the exopolysaccharide (EPS) of a mono-species biofilm and to infect the cells.
Hanlon et al. (2001) have recently demonstrated the ability of P. aeruginosa phage to diffuse through alginate gels at alginate concentrations up to 8% (wt/vol), and to bring about a 2-log reduction in the cell numbers in 20-day-old biofilms of P. aeruginosa. Samples of commercial alginate and purified cysticfibrosis (CF) alginate were incubated with 2×108 purified phage per ml for 24 h at 37° C., and the viscosity of phage-treated samples were reduced by up to 40% compared to those of controls incubated in the absence of phage. The alginate treated with phage had a lower molecular weight than untreated alginate, and the evidence suggested that the reduction in alginate viscosity was brought about by enzymic degradation derived from the bacterial host itself (ie. endogenous to the bacterial host cell).
Of the infections listed in Table 1, one of the most problematic infections to treat is that of cystic fibrosis pneumonia.
Most cystic fibrosis (CF) patients suffer from recurrent and chronic end-bronchial Pseudomonas aeruginosa infections. Intervention strategies include eliminating cross infection, and early aggressive antibiotic treatment. An inflammatory response occurs resulting in a shift of the organism's phenotype from non-mucoid to a mucoid phenotype. This alginate-producing phenotype then grows as an endo-bronchial biofilm, which is impossible to eradicate through antibiotic therapy.
There is therefore a need for alternative approaches for the treatment of infectious biofilms, preferably those associated with cystic fibrosis.
Phage may be highly specific in the destruction of their targets and, unlike antibiotics, do not interfere with natural flora. Combinations of different phage may be employed in the present invention. For example, phage cocktails may be tailored to target particular bacterial types present in a targeted biofilm. In this regard, different phage may be selected to target different (or the same) bacterial strains, species or genera present in a targeted biofilm.
Phage are easy to produce and are a cost-effective form of therapy.
Phage may be formulated in combination with one or more pharmaceutically-acceptable anti-microbial agents. In this regard, combinations of different antimicrobial agents may be tailored to target different (or the same) microorganisms, which contribute towards morbidity and mortality. The pharmaceutically-acceptable anti-microbial agents of the present invention are suitable for internal administration to an animal (preferably human), and therefore exclude industrial sterilizing chemicals such as detergents, disinfectants, and ammonium-based chemicals (eg. quaternary ammonium compounds such as QUATAL). Such sterilizing chemicals are typically used in the art for sterilizing industrial work surfaces (eg. in food processing, or hospital environments), and are not suitable for administration to an animal.
Phage may be used to treat immuno-compromised individuals or patients that have an allergy to antibiotics.
Phage can be stored for very long periods with no obvious loss of activity.
Phage resistant host strains of Ps. aeruginosa can be identified quickly and new varieties of phage can be readily generated to overcome resistance.
The therapeutic use of phage has been widely used in Eastern Europe for over 60 years with no reported significant adverse effects.
The bacteriophage preferably targets one or more of the bacteria listed in Table 1.
The bacteriophage preferably targets one or more of the bacteria listed in Table 1. Particularly preferred bacterial targets include one or more of:- Staphylococcus aureus; Haemophilis influenzae; Pseudomonas aeruginosa; Burkholderia cepacia;
Streptococcus pneumoniae; Stenotrophomonas maltophilia; Alcaligenes xylosoxidans; non-tuberculous mycobactefia; Mycobacterium bovis; Mycobacterium smegmatis; Mycobacterium tuberculosis; Burkholderia multivorans; Burkholderia stables; and Burkholderia vietnamesis. In terms of simple nomenclature, the bacteriophages are usually identified by reference to the bacteria that they infect. Thus, a bacteriophage that infects a mycobacterium may be referred to as a mycobacteriophage.
The present invention is preferably concerned with the treatment of biofilm-associated opportunistic infections, and particularly with the treatment of such infections in lung biofilms (eg. those associated with CF patients). Thus, the highly preferred bacterial targets of the present invention are Pseudomonas sp. and/or Burkholderia sp., especially Ps. aeruginosa and/or B. cepacia.
Preferred bacteriophage for use against the above bacterial targets have a high affinity for the bacterial target strain, and a high burst size. Said phage preferable encode a polysaccharide lyase (eg. an alginate lyase). Where the bacterial target is Ps. aeruginosa, preferred bacteriophage include ΦDGH4, ΦDGH6, ΦDGH13 and ΦDGH14.
A biofilm matrix typically comprises a high proportion of water (see Table 2), although this would depend on the specific biofilm system examined. Apart from water and microbial cells, the biofilm matrix is a complex of absorbed nutrients and metabolites, products from cell lysis, particulate material from the immediately surrounding area and secreted polymers. All major classes of macromolecules, protein, polysaccharides, DNA and RNA can be present in addition to peptidoglycan, lipids and other cell components.
Table 2—Typical Range of Biofilm Matrix Composition
The production of exopolysaccharides (EPS) is essential to the development of the architecture of the biofilm. It provides a framework into which microbial cells are inserted, and may also serve as a nutrient source for sessile cells.
In use of the present invention, a polysaccharide lyase enzyme is preferably selected such that it is capable of breaking down a component of the biofilm of interest. It is particularly preferred that the enzyme is capable of breaking down a component of the biofilm that is produced by a bacterium associated with (eg. residing within) the biofilm.
Alginate is the major extracellular product of biofilm-forming bacteria such as mucoid strains of Ps. aeruginosa. The latter chronically colonise the cystic fibrosis (CF) pulmonary cavity, and the resulting alginate glycocalyx acts as a barrier for Ps. aeruginosa sessile cells to antimicrobial agents and host defences. Thus, the mucoid form of Ps. aeruginosa is much more difficult to treat and is invariably associated with a poor prognosis for CF patients. Novel methods of eradicating this mucoid form of the organism are therefore essential for successful treatment of these chronic infections.
Alginate is a linear polysaccharide comprised of 1-4 linked β-O-mannuronic acid (M) (O-acetyl substitution on 2 and/or 3 position) and α-L-guluronic acid (G) monomers, which can either be arranged in homopolymeric (poly-guluronate GGGG, poly-mannuronate MMMM) or heterpolymeric (random sequences MGMG) regions. structures) may be present within a single alginate molecule. Thus, the preferred “first polysaccharide lyase” of the present invention is an alginate lyase and has a high affinity for at least one of (preferably both) M and G rich regions. The lyase may be encoded by the phage of the present invention, or may be exogenous with respect to the phage. It is also beneficial for the lyase to exhibit endo-cleaving activity (i.e. it can break up long linear alginate chains within their complex blocks of monomeric units, as opposed to exolytic activity in which monomers are removed from the ends of the polymer), thus breaking down the viscous long chained polymer into more aqueous oligosaccharide shorter chain products.
The presence of a DNase may help to break down DNA from dead patient host cells (eg. lung epithelial cells) within a biofilm, and may help to dissolve mucus components associated with a biofilm.
Defensins are a group of gene-encoded antimicrobial peptides that have been identified from a diverse range of organisms, such as vertebrates, invertebrates, plants and bacteria. In mammals, defensins are part of the innate host defence mechanism and are present in phagocytic cells and epithelial cells. They show a potent activity towards microorganisms, and are particularly useful for targeting antibiotic resistant bacteria [see Hancock, R. E. and Chapple, D. S. (1999) Antimicrobial Agents and Chemotherapy, vol. 43, No. 6, pp. 1317-1323]. By way of example, the following defensins are suitable for use in the present invention:
(1999). Of particular mention is the polymyxin family of antimicrobial polypeptides, especially polymyxin E (ie. Colistin) and polymyxin B.
Defensins (eg. polymyxins) are bactericidal in preferred concentrations of up to 8 μg ml−1, more preferably 1-5 μg ml−1.
Preferred defensins are those that attach to bacterial cell membranes (especially those rich in phosphatidylethanolamine), and disrupt the osmotic properties and transport mechanisms of the membrane.
Further examples of defensins, which are suitable for use in the present invention, are provided by U.S. Pat. No. 5,242,902, U.S. Pat. No. 5,641,497, WO89/11291, WO94/21672, U”2002/0037260, and WO95/32287.
Antibiotics are well known in the art, and may be employed in the present invention. Of particular mention is the aminoglycoside family of antibiotics, which were originally obtained from Streptomyces species, and in particular tobramycin. Antibiotics (eg. tobramycin) are bactericidal in preferred concentrations of up to 8 pμml−1, more preferably 1-5 μg ml−1. A typical antibiotic dosage regime according to the present invention for treating CF patients is the administration of 80 mg of antibiotic, preferably tobramycin, by nebulisation twice a day. As there is little adsorption from the mucosa, serum levels of tobramycin are unmeasurable. Further examples of anttibiotics, which are suitable for use in the present invention, are provided by US2002/0037260.
According to one embodiment of the invention, the antibiotic acts by inhibition of ribosomal protein synthesis. Preferred antibiotics according to this embodiment are members of the aminoglycoside family. A particularly preferred antibiotic according to this embodiment is tobramycin.
Another preferred class of antibiotics is the Polymxin family, particularly Polymyxins E (Colistin) and B. Colistin is bactericidal for Gram-negative bacilli including Pseudomonas spp. in preferred concentrations of up to 8 μg ml−1, more preferably 1-5 μg ml−1. Polymyxins, such as Colistin, are preferably used as topical agents due to poor absorption of these antibiotics from the gut. It is preferred that Colistin is administered as of Colistin sulphate, which is the stable water-soluble form. A typical dosage regime for CF patients is the administration of 2 mega units of Colistin by nebulisation twice a day. As there is little adsorption from the mucosa, serum levels of Colistin are unmeasurable.
According to one embodiment of the invention, the preferred antibiotic acts by attachment to bacterial cell membranes rich in phosphatidylethanolamine and disruption of the osmotic properties and transport mechanisms of the membrane. Preferred antibiotics according to this embodiment are members of the Polymyxin family, particularly Colistin.
Further antibiotics of particular mention are ciprofloxacin (preferably administered orally) and ceftazidime (preferably administered intravenously).
The bacteriophage may be a wide spectrum phage. For example, it may target several different species within a given genus, or may even target bacteria within different genera. Alternatively, the bacteriophage may be a narrow spectrum phage. For example, it may be specific to a given bacterial genus, species, or strain. The bacteriophage is capable of infecting a bacterium present in the biofilm of interest.
In a most preferred embodiment the invention provides a composition for treating a lung biofilm in a CF patient, preferably a biofilm comprising Pseudomonas aeruginosa and/or Burkholderia cepacia. The composition according to this embodiment preferably comprises a bacteriophage that encodes a polysaccharide lyase, preferably an alginate lyase enzyme. Alternatively, the enzyme may be provided exogenously.
A preferred bacteriophage according to the present invention is a bacteriophage selected from the GH group of phage such as GH4, GH6, GH13, GH14 (ECACC accession numbers 02121203, 02121202, 02121201, and 02121204 respectively, deposited by the applicant in ECACC on 12 Dec. 2002). A particularly preferred phage is bacteriophage ΦGH4.
Also provided is use of the composition in manufacture of a medicament for treatment of a bacterial biofilm. A preferred target is a lung biofilm in a CF patient.
Preferably the medicament is administered in more than one dose, more preferably in at least 3 separate doses (eg. per day). It is also preferred that administration of the medicament results in a reduction in the bacterial cell count of the biofilm of at least one log, preferably at least three logs.
According to a second aspect, the invention provides a bacteriophage comprising a heterologous gene encoding a polysaccharide lyase enzyme (eg. an alginate lyase). Preferably, the bacteriophage specifically infects a bacterial species or strain present in the biofilm. The polysaccharide lyase encoded by the modified bacteriophage should preferably degrade a specific polysaccharide produced by a bacterial species or strain present in the biofilm. In a particularly preferred embodiment, the biofilm comprises Ps. aeruginosa and/or B. cepia.
The bacteriophage may optionally comprise more than one hetererologous gene encoding more than one polysaccharide lyase (eg. an alginate lyase). Said enzymes are preferably different, and therefore degrade different exopolysaccharide (EPS) components of a biofilm. The terms EPS and polysaccharide are used interchangeably in the biofilm context of the present invention. The bacteriophage may also encode a DNase, and/or a pharmaceutically-acceptable antimicrobial agent (eg. an antibiotic, and/or defensin).
The modified/recombinant bacteriophage, like the “composition” first aspect of the present invention, may be used to treat biofilms such as those resulting from opportunistic bacterial infections. For example, chronic lung infections in CF patients may be treated. In particular, the modified/recombinant bacteriophage may be used as part of the “composition” aspect, and thus may be employed with one or more pharmaceutically-acceptable antimicrobial agents, a second or further (preferably different) polysaccharide lyase enzyme (eg. an alginate lyase), and/or a DNase.
In another embodiment, the “composition” aspect may include two or more modified/recombinant bacteriophage. For example, the composition may include a first and second bacteriophage, wherein the first bacteriophage comprises a gene encoding a first polysaccharide lyase enzyme, and the second bacteriophage comprises a gene encoding a second polysaccharide lyase enzyme, and wherein the first and second polysaccharide lyase enzymes are not the same. The first and second bacteriophage may be the same or different.
In a related “composition” embodiment, a cocktail of naturally-occurring and modified/recombinant bacteriophages may be employed in combination. The first polysaccharide lyase may be provided exogenously or may be encoded by one or more of the bacteriophage, and additional (preferably different) lyases may be included. Not all bacteriophage employed in a composition of the present invention need encode a polysaccharide lyase. Such bacteriophage may possess, for example, enhanced bacteriolytic activity vis-a-vis other bacteriophage with respect to biofilm-associated bacteria.
Other bacteriophage suitable for use in the present invention are publicly available from the American Type Culture Collection and have the following accession numbers ATCC 12055-B1, ATCC 12055-B2, ATCC 12055-B3, ATCC 14205-B1, ATCC 14206-B1, ATCC 14207-B1, ATCC 14209-B1, ATCC 14210-B1, ATCC 14211-B1, ATCC 14212-B1, ATCC 14213-B1, ATCC 14214-B1, ATCC 15692-B2, ATCC 15692-B3, ATCC 25102-B1, ATCC BAA-26-B1, ATCC BAA-27-B1, ATCC BM-28-B1, ATCC BAA-28-B2, ATCC BAA-29-B1, ATCC BAA-30-B1, ATCC BAA-31-B1, ATCC BAA47-B1, ATCC BAA-79-B1, ATCC BM-81-B1, and ATCC BAA-81-B2.
The invention also provides a method of making a modified/recombinant bacteriophage capable of degrading a biofilm comprising:
In one embodiment, the bacteriophage is selected from the group consisting of GH4, GH6, GH13, GH14 (ECACC accession numbers 02121203, 02121202, 02121201, and 02121204), or bacteriophage having accession numbers ATCC 12055-B1, ATCC 12055-B2, ATCC 12055-B3, ATCC 14205-B1, ATCC 14206-B1, ATCC 14207-B1, ATCC 14209-B1, ATCC 14210-B1, ATCC 14211-B1,ATCC 14212-B1, ATCC14213-B1, ATCC 14214-B1, ATCC 15692-B2, ATCC 15692-B3, ATCC 25102-B1, ATCC BAA-26-B1, ATCC BM-27-B1, ATCC BM-28-B1, ATCC BM-28-B2, ATCC BM-29-B1, ATCC BM-30-B1, ATCC BAA-31-B1, ATCC BMA47-B1, ATCC BAA-79-B1, ATCC BM-81-B1, and ATCC BAA-81-B2.
In a preferred embodiment, the polysaccharide lyase enzyme is an alginate lyase. The modified phage is preferably capable of infecting (eg. lysing) a bacterium selected from Ps. aeruginosa and/or Burkholderia cepacia.
The method may include analysis of the biofilm to identify a bacterial species or strain within the biofilm. The biofilm is preferably a clinical sample, such as a sample taken from an infected patient (eg. a lung sample taken from a CF patient).
In a preferred embodiment the bacteriophage is specific for a bacterial species or strain present in the biofilm.
In one embodiment the polysaccharide lyase enzyme recited in step a) may be selected by use of a bank of specific enzymes, which may be tested individually on the biofilm for degradative activity. Thereafter, biofilm degradation may be confirmed by turbimetric analysis, viscometry, or chromatographic analysis.
In a further (or simultaneous) method step, one or more genes encoding a second polysaccharide lyase, and/or a pharmaceutically-acceptable antimicrobial agent, and/or a DNase may be introduced into the bacteriophage nucleic acid.
It is preferred that the efficacy of the modified bacteriophage be tested in vitro prior to use against infections in a clinical context.
A bacteriophage prepared as above may be employed in the treatment of a biofilm-associated microbial infection as described in the preceding aspects of the present invention.
According to further aspect the invention provides a method of identifying a bacteriophage for use in treatment of a biofilm-associated microbial infection, which method comprises:
In a preferred embodiment, the polysaccharide lyase enzyme is an alginate lyase. The phage is preferably capable of infecting (eg. lysing) a bacterium selected from Ps. aeruginosa and/or Burkholderia cepacia.
The method may include analysis of the biofilm to identify a bacterial species or strain within the biofilm, and/or a polysaccharide component within the biofilm or a polysaccharide produced by the microorganisms of the biofilm.
The presence of polysaccharide lyase enzyme activity may be confirmed by 30 monitoring biofilm degradation (eg. by turbimetric analysis, viscometry, or chromatographic analysis).
The biofilm is preferably a clinical sample, such as a sample taken from an infected patient (eg. a lung sample taken from a CF patient).
In a preferred embodiment the bacteriophage is specific for a bacterial species or strain present in the biofilm.
The identified bacteriophage may be modified according to the second aspect of the invention so that it encodes a further polysaccharide lyase, an antibiotic, a DNase, and/or a defensin.
The method may include a further step of testing the efficacy of the selected bacteriophage against a sample of the biofilm in vitro.
Said bacteriophage may be employed in the treatment of a biofilm-associated microbial infection as described in the preceding aspects of the present invention.
According to another aspect of the present invention there is provided a method of treating biofilm-associated infections.
In operation, the method involves administration of at least one dose, preferably at least three doses, of bacteriophage plus first polysaccharide lyase to the site of infection. Administration is preferably via aerosol delivery. The phage and first polysaccharide may be administered at the same time, prior to, or subsequently to one another.
According to a preferred aerosol delivery embodiment, the particle size in the aerosol is between 100 μm and 1 μm. In more detail, a particle size of approximately 60 μm targets biofilms in the upper respiratory tract, whereas a particle size of 2-4 μm targets biofilms at or near the alveoli. Thus, the aerosol may have a broad delivery range (ie. contain particles of 1-100 μm), or may have a narrow delivery range (eg. 2-20 μm for targeting the lower airways, or 40-100 μm for targeting the upper airways). antibiotic, a DNase and/or a defensin, either at the same time, prior to, or subsequently to administration of the bacteriophage.
In one embodiment, the repeated use of phage and polysaccharide lyase, optionally plus a pharmaceutically-acceptable antimicrobial agent (eg. an antibiotic, and/or defensin), is employed.
The medical treatment aspect of the present invention has particular benefits in treating CF patients and helps to prevent the re-colonisation of parts of the lung by cells that have been released from the biofilm.
The above prophylactic or curative method is particularly suitable for treatment of biofilm infections of the lung and gastrointestinal tract, and biofilms present on medical devices such as catheters, intra-vascular devices, prosthetic devices and dental implants. In particular, biofilm disruption according to the present invention enables access of antimicrobial agents (eg. antibiotics, and/or defensins) and other phage to microorganisms residing deep within said biofilm. Such access is not otherwise possible with the isolated use of an antimicrobial agent.
The invention is illustrated by the following drawings, in which:
The present invention allows the isolation and characterisation of bacteriophage that are able to lyse clinical Ps. aeruginosa isolates. Bacteriophage are characterised with regard to their potential virulence based on assessment of host range, burst size and efficiency of lysis. The ability of selected phage to lyse sensitive host strains in sputum samples is evaluated and these phage evaluated further in an in vitro biofilm model simulating infection with mucoid and non-mucoid strains.
The present invention preferably relates to specific bacteriophage, which offer the potential to control Ps. aeruginosa induced biofilm formation and, in particular, biofilms involving the more aggressive drug resistant bacterial species that contribute significantly to morbidity and mortality in CF patients.
A chemostat system has been developed to generate continuous Pseudomonas aeruginosa culture. The culture provide inocula for biofilm studies using a Robbins device.
The chemostat vessel consists of a 2-litre glass vessel with titanium top plates. The plate is fitted with various probes (pH, temperature and Redox) which allow the physical parameters within the vessel to be monitored and maintained under defined controlled conditions. A FT Applikon fermenter controller regulates these environmental conditions.
A Robbins device is used to study biofilm formation. The device provides quantifiable samples of biofilms growing on submerged surfaces in an aqueous environment which can be monitored over a time course. It consists of a hollow rectangular acrylic tube with twenty five evenly spaced sampling ports. Each port allows insertion of a sampling stud that contains a polyvinyl chloride (PVC) disk that lies flush to the upper surface of the lumen. The continuous culture is pumped through the Robbins device and biofilms are formed on the surface of PVC disks exposed to the culture. A series of Robbins devices may be run in each experiment. This allows the evaluation of different regimes to reduce biofilm development under identical controlled conditions.
1. Components of the Culture System
Upstream of each Robbins device inlet tubes have a ‘Y’ junction. One line was designated as an inlet port (Port A) and is connected either to the chemostat or a sterile media reservoir. The other line was an inoculation port (Port B) that allowed the inoculation of the Robbins lumen with test agents.
Outlet tubes downstream of the Robbins device also have a ‘Y’ junction. One line was designated waste and led to a Robbins device waste reservoir (Port C). The other line led to a sterile universal container (UC) and was used to collect planktonic samples from the Robbins device lumen (Port D).
During initial biofilm development, the inoculation and planktonic sample ports were clamped (ports B and D) and the inlet line (A) was connected to the chemostat.
At this time point, studs (x 3) were removed from the Robbins to enumerate biofilm density.
The biofilm was then infected with bacteriophage/tobramycin or both simultaneously.
At predetermined time intervals (1 h, 2 h, 4 h, 6 h, 18 h, 12 h, 18 h, 24 h and 48 h) studs were removed from the Robbins device and replaced with sterile studs as stated in process iii-iv. Coupons were detached from the studs, sonicated and vortex mixed to remove biofilm as in process v-vii. Planktonic and biofilm associated bacteria and phage were then enumerated as stated below:
Bacteriophage titre was calculated using an agar overlay infection with exponentially grown Ps. aeruginosa.
Preparation of Log Phase Culture
Agar Overlay Method
Biofilms of mucoid Ps. aeruginosa developed using a Robbins device were shown to be degraded by the administration of alg L carrying phage.
A series of multiple dose experiments were performed to compare the efficacy of biofilm removal with phage against tobramycin, a front line aminoglycoside antibiotic used to treat CF patients. Resultant data showed that four applications at the minimal inhibition concentration (MIC) over a 24 hour period had no significant effect on the Ps. aeruginosa sessile population (
A combined regime of phage φGH4 and tobramycin at the MIC level (
A) Isolation of Lytic Bacteriophage Against Clinical Ps. aeruginosa Strains:
Clinical samples were collected from Liverpool Medical School and screened against our 22 clinical Ps. aeruginosa strains and two control strains (NCTC 6750, ATCC 27853). A further 9 lytic bacteriophage were obtained from this study thus bringing the current phage collection to twenty. All isolated phage were enriched against their corresponding host and subsequently stored at 4° C. and −70° C.
B) Alginate Lysis:
At least three of the phage in the collection appeared to exhibit putative alginase activity. Using a turbidimetric procedure developed by Kitamikado et al. (1990) we have confirmed that these phage mediate the production of alginate lyase during the lytic cycle. The enzyme is present in phage induced cell lysates but is not found in uninfected cell lysates or in purified phage preparations.
C) In Vitro Biofilm Model:
Biofilms of mucoid Ps. aeruginosa developed using a Robbins device were shown to be degraded by the administration of phage.
A series of multiple dose experiments were performed to compare the efficacy of biofilm removal with phage against tobramycin, a front line aminoglycosidic antibiotic used to treat CF patients. Resultant data showed that four applications of minimal inhibition concentration (MIC) and 10× MIC Tobramycin over a 48 hour period had no significant effect on the Ps. aeruginosa sessile population. When a dual infection regime of ΦGH4 and MIC tobramycin was tested a three-log reduction in biofilm cells was accompanied by a significant decrease in viability of released biofilm cells (i.e. Ps. aeruginosa cells released from the biofilm through the action of phage breaking open the biofilm).
D) Stability and Lytic activity of Phage in Sputum:
To ensure effective treatment of cystic fibrosis pulmonary Ps. aeruginosa infections bacteriophage should exhibit lytic activity in the viscid sputum/mucin rich environment of the CF lung. In vitro phage infection assay performed with mucoid Ps. aeruginosa GH56 and phage ΦGH4 in sputum (free of indigenous Ps. aeruginosa) recovered from CF patients showed that the phage remains stable and retains greater than 90% lytic activity. Similar results were obtained with lytic infections performed in 5% mucin.
E) Stability and Lytic Activity of Phage Following Aerosolisation:
Delivery of phage to the CF lung preferably takes the form of a non-invasive inhalation system. Phage should therefore retain viability following aerosolisation. A Colison nebuliser coupled to a Henderson Apparatus was used to aerosolise a specific volume of a known titre of phage ΦGH4. This process generates aerosols in the region of 4 mm which are the optimum size for successful transportation to the alveoli at the base of the lungs. Resultant aerosols were collected, quantified and tested for lytic activity against Ps. aeruginosa GH56. Results showed that less than 5% of the phage were lost due to aerosolisation and that the phage retained >90% lytic activity against P. aeruginosa GH56 following passage through the Henderson Apparatus/Collison nebuliser.
Twenty phage have been isolated from the environment and clinical specimens. The phage lyse clinical Ps. aeruginosa strains, which strains exhibit different host ranges.
Exopolysaccharide (EPS) normally protect bacterial biofilm cells against the majority of bacteriophage (Weiner et al., 1995). In the case of Ps. aeruginosa pulmonary infections, the bacterial biofilm is encapsulated within a thick alginate matrix. At least three of the phage we have isolated exhibit polysaccharide lyase (alginase) activity against a specific Ps. aeruginosa alginate. This is important in treating such infections, as the phage may illicit a two pronged attack on mucoid Ps. aeruginosa biofilms in degrading its way through the biofilm alginate thus gaining access to the underlying susceptible bacteria. The turbidimetric alginase assay confirms that the enzyme is only present during the lytic cycle of phage infection, and we have confirmed that the alginase activity is phage encoded.
Of great interest are the results obtained with dual therapy of bacteriophage and tobramycin. We hypothesised that removal of Ps. aeruginosa cells from the alginate rich biofilm environment renders the previously resistant cells sensitive to tobramycin. This infection regime therefore generates a synergistic effect on Ps. aeruginosa both within the biofilm and bacilli released from the biofilm through the action of alginate lyase phage.
The observation that phage infection and cell lysis was not inhibited in the presence of sputum or by the process of aerosolisation demonstrates that the inhalation conveyance system of phage aerosols would ensure delivery of viable lytic phage into the sputum rich lung alveoli of CF patients.
Method for the insertion of a heterologous alginase gene into a bacteriophage.
Where the DNA sequence of the lyase (eg. alginase) gene has been determined, direct cloning may be employed by PCR using a primer designed upstream of the sequence and a complementary reverse primer downstream. For the A. chroococcum algL gene, the DNA sequence is publically available on Genbank under Accession No. AJ223605, and a pair of suitable primers includes GGACTGAACTTCTTCGCC (forward primer) and GCTGCTGCTGGATCGGC (reverse primer). The primers may further comprise restriction sites at their 5′ ends to facilitate cloning. These primers 30 are suitable for PCR amplification of the complete lyase (eg. algL gene from A. chroococcum) using a proof-reading DNA polymerase to ensure the cloning of a active gene product. A conventional alginase assay is then employed to confirm the presence of alginase activity.
The second method is employed where the relevant DNA data are not available, and involves the preparation of a gene library of the selected bacteria or bacteriophage containing the alginase in a plasmid such as pUC19 in E. coli. The gene library is then screened for alginase activity by a conventional alginase assay, and the clone carrying the alginase gene identified.
Isolation of Pseudomonas aeruginosa and Burkholderia cepacia from Clinical Samples 30
Any growth on Pseudomonas CFC medium indicates the presence of Pseudomonas spp. The presence of blue/green or brown pigmentation may be taken as presumptive evidence of P. aeruginosa.
Growth on Pseudomonas CN medium indicates presence of P. aeruginosa.
B. cepacia typically grows as smooth, glistening red/purple colonies of approximately 2 mm diameter on P. cepacia media. Specific strains may grow as atypical forms including lipolysaccharide deficient strains with dwarf, rough colonial appearance and a diffusible brown melanin-like pigmentation.
Our collection of bacteriophage can now be examined for lytic activity against the test isolate using the agar overlay method.
Preparation of Log Phase Culture
Following incubation, plates are then examined for lysis, and the number of plaque forming units per ml recorded (pfu ml−1).
Isolation of Biofilm Alginate
Bacterial constituents of the biofilm must firstly be isolated as a pure culture (see Example 3; Isolation of Pseudomonas aeruginosa and Burkholderia cepacia from clinical samples).
Our test alginate lyase preparation/bacteriophage carrying alginate lyase is then examined for its ability to lyse clinically isolated alginate using the turbidimetric procedure developed by Kitamikado et al. (1990).
Mice were infected with Ps. aeruginosa at day zero, and the infection allowed to establish. The average recovery of Ps. aeruginosa from infected mice (n=6) was 4.28±0.59 Log CFU.ml−1.
At day 10 mice were exposed to aerosolised bacteriophage. Phage and bacteria were then recovered from the mice at 6 and 24 hours post-aerosol challenge (see
Phage Counts
Recovery of phage at 6 h=5.97±0.34 Log CPU.ml−1.
Recovery of phage at 24 h=5.05±1.91 Log PFU.ml−1.
Pseudomonas Counts
Pseudomonas recovered after 6 h=0.53±0.83 Log CFU.ml−1.
Pseudomonas recovered after 24h =0.0.57±1.04 Log CFU.ml−1.
Results
Results demonstrate a decrease of 3.75 Log CFU.ml−1 in the number of Ps. aeruginosa after challenge with bacteriophage. These results are significantly different (P<0.05).
| Number | Date | Country | Kind |
|---|---|---|---|
| 0300597.2 | Jan 2003 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB04/00073 | 1/12/2004 | WO | 1/26/2006 |
