Patent Application
20180011091
The present invention pertains to the field of diagnostics, particularly methods and systems for diagnostic testing of bacterial infections in organisms, including humans, using recombinant bacterial glycoproteins.
Pathogenic bacteria have been responsible for millions of deaths of humans, cattle and other animals. Infection from bacteria has caused such diverse conditions as the bubonic plague, pneumonia, tuberculosis, anthrax, and methicillin-resistant Staphylococcus aureus (MRSA) infection which is becoming increasingly problematic in hospital environments. Thus, it is important to diagnose and treat bacterial infections to reduce the burden on the health-care system and the population as a whole.
There have been numerous methods developed that can be used to diagnose bacterial infections. Common tests include sputum, blood and urine tests which, historically, offer limited information regarding the severity of the infection. Tests can be non-specific as to the identity of the infecting bacteria and are often inaccurate. Such tests can be designed to detect the presence of the bacteria directly (e.g., by detecting a characteristic protein or nucleic acid), or indirectly, for example, by detecting antibodies that the infected individual has developed in response to the bacterial infection.
Immunoassays using lipopolysaccharide (LPS) from bacteria as an antigen, have been developed (see, for example, Lindberg, et al. “Enzyme immunoassay of the antibody response to Brucella and Yersinia enerocolitica O9 infections in humans” J. Hyg. 1982, 88(2):295-307; and Lindberg, et al. “Shigellosis in Vietnam: seroepidemiologic studies with use of lipopolysaccharide antigens in enzyme immunoassays” Rev. Infect. Dis. 1991, 13 Suppl 4:S231-S237). LPSs are large molecules that comprise an O antigen (or O polysaccharide), a core polysaccharide and Lipid A. LPS is the major component of Gram-negative bacteria and, consequently, recombinant or isolated LPS has been used in immunoassays for Gram-negative bacteria. However, these assays suffer from false positives as a result of the high immunogenicity of the LPS antigen (see, for example, Eoh, et al. “Expression and Validation of D-Erythrulose 1-Phosphate Dehydrogenase from Brucella abortus: A Diagnostic Reagent for Bovine Brucellosis” 2010, 22(4):524-530). For example, antibodies against the Lipid A core often cause false positives in immunoassays that employ LPS.
The use of recombinant bacterial glycoproteins to diagnose Gram-negative bacterial infections has been previously suggested by Castric et al. in U.S. Patent Publication No. U.S. 2002/0039755 and International PCT application publication number WO 1997/023600. However, this suggested use has serious disadvantages. In Castric et al., it is suggested that Gram-negative bacterial infections can be diagnosed by detecting antibody complexes formed between pilin-glycan conjugates produced using the oligosaccharyl transferase enzyme PilO from Pseudomonas aeruginosa. No actual assay was performed in Castric et al. Unfortunately, reliance on PilO severely limits both the type of O-antigen repeating units and the type of glycoprotein that can be detected. PilO only transfers short glycan chains to the C-terminal serine residue of one protein, specifically pilin (Castric et al. in U.S. Patent Publication No. U.S. 2002/0039755 and International PCT application publication number WO 1997/023600, Faridmoayer, et al. “Functional Characterization of Bacterial Oligosaccharyltransferases Involved in O-Linked Protein Glycosylation” J. Bacteriol, 2007, 189(22): 8088-8098). This limitation would severely restrict the type of bacterial infections that may be detected and the sensitivity of the assay, if the assay were even functional.
There remains a need for additional diagnostic assays for detection of bacterial infection.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.
An object of the present invention is to provide a method of diagnosing bacterial infections using engineered glycoproteins.
The present application provides a method of diagnosing bacterial infections using engineered glycoproteins in an immunoassay. The engineered bacterial glycoproteins used in the immunoassay comprise a bacterial antigen covalently attached to a protein via polysaccharyltransferase (PTase)-mediated glycosylation, wherein the bacterial antigen is selected based on the bacterial infection of interest. Antibodies in a bodily fluid of subjects infected with a bacteria will bind to the engineered glycoprotein, and the resulting binding complexes are detected or quantitated.
In accordance with one aspect, there is provided a method of detecting a bacterial infection in a subject suspected of having a bacterial infection, the method comprising: contacting the sample with a mixture of one or more glycoproteins; and detecting the presence or absence of a bacterial infection by detecting the presence or absence of a complex formed between the glycoproteins and antibodies specific therefor in the sample, wherein each of said glycoproteins comprises a bacterial antigen covalently attached to a protein via polysaccharyltransferase (PTase)-mediated glycosylation.
Optionally, the step of detecting antibody-glycoprotein binding complexes comprises incubating the sample and one or more glycoproteins with a secondary antibody that specifically binds to the anti-bacterial antibody or to the antibody-glycoprotein binding complexes.
In accordance with another aspect, there is provided an immunoassay kit for diagnosing a bacterial infection in a subject, the kit comprising: a mixture of one or more glycoproteins, wherein each glycoconjugate comprises a bacterial antigen covalently attached to a protein via polysaccharyltransferase (PTase)-mediated glycosylation; and instructions for contacting the mixture of glycoconjugates with a sample of bodily fluid from the subject and monitoring for formation of binding complexes formed by binding of the glycoproteins by antibodies in the sample that are specific for bacterial polysaccharides.
In accordance with one embodiment, there is provided a kit for diagnosing a bacterial infection in a subject, the kit comprising: a solid medium comprising having one or more glycoproteins immobilized on a surface thereof, wherein each of said glycoproteins comprises a bacterial antigen covalently attached to a protein via polysaccharyltransferase (PTase)-mediated glycosylation; and instructions for contacting the solid medium with a sample of bodily fluid from the subject and monitoring for formation of binding complexes formed by binding of the glycoproteins by antibodies in the sample that are specific for bacterial polysaccharides.
In accordance with another aspect, there is provided a method for diagnosing a bacterial infection in a subject comprising: contacting a sample obtained from the subject with a glycoprotein comprising a bacterial polysaccharide covalently attached to a protein; and detecting first binding complexes formed by binding of the bacterial polysaccharide in the glycoprotein to antibodies present in the sample that are specific for the bacterial polysaccharide, wherein the bacterial polysaccharide and the protein are from different bacterial species, and wherein the presence of binding complexes is indicative of a bacterial infection in the subject.
Definitions
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
As used in the specification and claims, the singular forms “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.
The term “comprising” as used herein will be understood to mean that the list following is non-exhaustive and may or may not include any other additional suitable items, for example one or more further feature(s), component(s) and/or ingredient(s) as appropriate.
As used herein, the term “immunoassay” refers to biochemical test used to qualitatively or quantitatively detect the presence of a substance in a sample.
As used herein, the term “target antibody” refers to an antibody specific for a bacterial antigen from a bacteria suspected of infecting a subject. It is the presence or absence of the target antibody that is used as an indicator of bacterial infection in the subject.
As used herein, the term “bodily fluid” refers to a naturally occurring and/or secreted and/or excreted and/or discharged fluid and/or wash fluid from the surface or inside the bodies of a human or an animal and includes, but is not limited to: serum, plasma, blood, synovial fluid, pharyngeal, nasal/nasal pharyngeal and sinus secretions, saliva, sputum, urine, mucous, feces, chyme, vomit, gastric juices, pancreatic juices, semen/sperm, cerebral spinal fluid, products of lactation or menstruation, egg yolk, amniotic fluid, aqueous humour, vitreous humour, cervical secretions, vaginal fluid/secretions, bone marrow aspirates, pleural fluid, sweat, pus, tears, lymph and bronchial or lung lavage.
As used herein, a “glycoprotein” is a molecule comprising protein with covalently bound glycans.
As used herein, a “glycan” comprises any sugar that can be transferred (e.g, covalently attached) to a protein. A glycan can be a monosaccharide, oligosaccharide or polysaccharide. As described above, an oligosaccharide is a glycan having 2 to 10 monosaccharides. A polysaccharide is a glycan having greater than 10 monosaccharides. Polysaccharides can be selected from the group comprising O-antigens, capsules, and exopolysaccharides. Of course, one of skill in the art will appreciate that other types of polysaccharides may also be used.
When the glycoprotein is used as a component of the assay system described herein, at least a portion of the attached glycans are antigenic. This is described in more detail below.
Glycans useful herein include, but are not limited to, glycans from Brucella abortus, Yersinia pseudotuberculosis O9, C. jejuni, N. meningitidis, P. aeruginosa, S. enterica LT2, and E. coli. In one embodiment, the monosaccharide at the reducing end of the glycan is a hexose or an N-acetyl derivative of a hexose. In one aspect, the hexose can be galactose. In one aspect, the N-acetyl derivative of hexose can be selected from the group comprising N-acetylglucosamine (GIcNAc), 2-Acetamido-2,6-dideoxyhexose (FucNAc), and DATDH (2,4-diacetamido-2,4-,6-trideoxyhexose).
The present invention provides an immunological method for exploiting recombinant bacterial glycoproteins to detect antibodies directed against bacterial polysaccharides present in fluids of infected organisms. The method is useful for identifying or quantifying bacterial infection in a subject, such as a human or livestock.
The surface of bacteria includes polysaccharides, many of which are antigenic and will trigger an immune response upon infecting a host organism. That is, the infection will trigger the production of host antibodies specific for bacterial surface polysaccharides and glycoproteins. The present assay makes use of recombinant bacterial glycoproteins in an assay to detect such host antibodies.
While other methods for assaying and diagnosing bacterial infections have been described, none to date exploit the use of bacterial glycoproteins, particularly those generated by the activity of polysaccharyltransferases (PTases). The assay described in the present application provides a method of detecting bacterial antibodies in infected subjects.
The examples provided below demonstrate the production of recombinant glycoproteins and their successful use in the presently described assay in detecting Brucella and E. coli infections in humans and animals. This is indicative of the successful use of the assay for detecting any bacterial infection in a human or animal. For example, the present assay can be used to detect infection by any clinically important bacteria, which may be, for example, Salmonella, E. coli, Brucella, Shigella, Vibrio cholera, Neisseria meningitidis, Klebsiella, Citrobacter, Hafnia, Proteus, Haemohilus influenzae, Streptococcus pneumoniae, Staphylococcus, Group B streptococci, Yersinia pseudotuberculosis, Campylobacter jejuni, Acinetobacter baumannii and Pseudomonas aeruginosa. These bacteria have antigenic polysaccharides covering all or a portion of their surface.
Glycoproteins
The glycoproteins used in the immunological method described herein contain a glycosylated protein made by via PTase-mediated glycosylation. In particular, the present inventors have taken advantage of the promiscuity or flexibility of PTases to manufacture glycoproteins comprising protein glycosylated with bacterial antigens.
Protein glycosylation is a common posttranslational modification in bacteria, including both gram-negative and gram-positive bacteria. While the precise functions of the glycans attached to bacterial proteins have not been determined, glycoproteins may play roles in adhesion, stabilization of the proteins against proteolysis, and evasion of the host immune response (Faridmoayer et al., “Functional characterization of bacterial Oligosaccharyltransferases involved in O-linked protein glycosylation.” J. Bacteriology 2007;189(22):8088-8098, the entirety of which is incorporated herein by reference).
Glycans are generally attached to serine or threonine (O-glycosylation) or asparagine (N-glycosylation) residues. Two different mechanisms for protein glycosylation can be distinguished by the mode in which the glycans are transferred to proteins. The first mechanism involves the transfer of carbohydrates directly from nucleotide-activated sugars to acceptor proteins. Examples of pathways using this mechanism are protein O-glycosylation in the Golgi apparatus in eukaryotic cells, and flagellin O-glycosylation in several bacterial species. In the second mechanism, an oligosaccharide is preassembled onto a lipid carrier before being transferred to protein acceptors by an oligosaccharyltransferase (OTase) or polysaccharyltransferase (PTase). This mechanism has been described for N-glycosylation in the endoplasmic reticulum of eukaryotic cells and in the general N-glycosylation system of Campylobacter jejuni.
Bacterial OTases and PTases constitute a family of enzymes that serve in linking a wide variety of glycans to proteins in both prokaryotes and eukaryotes (Feldman et al. “Engineering N-linked protein glycosylation with diverse O antigen lipopolysaccharide structures in Escherichia coli.” Proc. Nat. Acad. Sci. 2005;102(8):3016-21; Wacker et al., “Substrate specificity of bacterial oligosaccharyltransferase suggests a common transfer mechanism for the bacterial and eukaryotic systems.” Proc. Nat. Acad. Sci. 2006;103(18)7088-93; Faridmoayer et al., “Extreme substrate promiscuity of the Neisseria Oligosaccharyl Transferase Involved in Protein O-Glycosylation.” J. Biol. Chem. 2008;283 (50):34596-34604; Iwashkiw poster, “Glycoengineering a novel brucellosis glycoconjugate vaccine.” Gordon Research Conference in Glycobiology, Ventura, Calif., 2009; all of which are incorporated herein by reference in their entirety).
Three bacterial oligosaccharyl and polysaccharyl transferases have been characterized to date: namely, Campylobacter PglB, Neisseria PglL; and Pseudomonas PilO. PglB attaches sugars to asparagine residues and belongs to a different family of PTases, similar to the eukaryotic transferases, than PglL and PilO. Both PglL and PilO attach sugars to serine residues and include a homologous domain. However, PglL and PilO differ significantly, for example in the glycans they are capable of transferring. PilO only transfers short glycan chains (i.e., oligosaccharides) to the C-terminal serine residue of one known protein (pilin) (Faridmoayer (2007), supra). As a result, this enzyme is referred to herein as an OTase. In contrast, PglL can transfer virtually any sugar including polysaccharides to internal serine residues in different proteins. Both PglB and PglL are referred to herein as PTases since they are capable of transferring polysaccharides to proteins.
In the immunoassay defined herein, engineered glycoproteins have been designed to be reactive with antibodies present in samples obtained from individuals having a bacterial infection. Polysaccharides are capable of acting as efficient binding partners with antibodies, whereas oligosaccharides are not efficient binding partners, which makes them unsuitable for use in sensitive immunoassays. Accordingly, the OTase PilO is not suitable for use in the manufacture of glycoproteins used in the present immunoassay. Rather PTases, such as PglB and PglL are effective in generating glycoproteins containing different polysaccharides, which are successfully used in the present immunoassay. Exemplary embodiments of the assay are described below.
The engineered glycoproteins useful in the present immunoassay can be prepared using PTases according to known methods (see, for example, PCT Publication WO2011/062615; US Patent Publication 2009/0735773; US Patent Publication 2009/0074798; US Patent Publication 2005/0192962; US Patent Publication 1999/0337393; PCT Publication WO1997/023600, Wacker, supra; Faridmoayer, supra, all of which are incorporated herein by reference in their entirety).
Generally, engineered glycoproteins are prepared by incubating a PTase with a selected acceptor protein and a lipid-linked glycan. The method can comprise introducing into a prokaryotic organism, in any particular order, at least a DNA comprising a gene that produces a PTase, and DNA comprising a gene that produces a protein to be glycosylated. The PTase facilitates the covalent attachment of the glycan(s) to the protein to produce the antigenic glycoprotein. When such glycoproteins are to be employed in an immunoassay as described herein the glycan comprises a polysaccharide, or combination thereof, identified as being immunogenic and/or suspected of being immunogenic.
The PTase makes use of a lipid carrier to transfer the glycan to the acceptor protein. In certain embodiments, the lipid carrier is a polyprenol-pyrophosphate including, but not limited to, undecaprenol-pyrophosphate, dolichol-pyrophosphate, and synthetic equivalents thereof. In other embodiments, the method further comprises introducing into the prokaryotic organism DNA comprising genes required for the assembly of a glycan onto a lipid carrier.
The use of PTases is particularly advantageous since they can be used to prepare glycosylated proteins without introducing limitations as to the type of glycan that can be added to proteins, the length of the glycan transferred, the type of sugar located at the reducing end of the glycan, the position of the glycan on the protein or the type of organisms that can be used.
The acceptor protein in the engineered glycoprotein can be any protein that functions as a substrate for PTase and, preferably, exhibits low immunogenicity in comparison to the polysaccharide. The low immunogenicity allows the polysaccharide component of the engineered glycoprotein to function as the antigenic component and minimizes false positives that can be caused by non-specific antibody binding during the immunoassay.
In a specific embodiment, the acceptor protein is the N-glycoprotein AcrA protein of Campylobacter jejuni. For the glycoprotein can comprise the AcrA of C. jejuni coupled to an O-antigen of Yersinia pseudotuberculosis O9 (AcrA-AO9), or a polysaccharide antigen of E. coli (e.g., AcrA-AO157).
Immunoassay
In accordance with one aspect, there is provided an immunological method, or an immunoassay system, for detecting in a sample of bodily fluid antibodies specific for a bacterial antigen. The presence or quantity of such antibodies can be useful in diagnosing bacterial infection in the subject from which the bodily fluid sample was obtained. The immunoassay described herein employs the engineered glycoprotein described above to form a binding complex with antibodies present in a bodily fluid sample that are specific for a bacterial antigen. The glycan component of the engineered glycoprotein used in the immunoassay is selected based on the specific bacterial infection to be assayed.
Immunoassays for detecting a target antibody of interest from samples may be either competitive or noncompetitive. In either case, the presence of a complex formed between the engineered glycoprotein described above and antibodies specific therefor can be detected by any of the known methods common in the art, such as, for example, fluorescent antibody spectroscopy or colorimetry.
As is well known in the field, noncompetitive immunoassays are assays in which the amount of captured target antibody is directly measured. In one preferred assay, for example, the engineered glycoprotein specific for the target antibody can be bound directly (immobilized) to a solid substrate or solid medium where the antibody will be immobilized upon forming a binding complex with the engineered glycoprotein. The target antibody/engineered glycoprotein complex thus immobilized is then bound by a labeling agent, such as a second or third antibody bearing a label.
In competitive assays, the amount of target antibody in a sample is measured indirectly by measuring the amount of an added (exogenous) target antibody displaced (or competed away) from a engineered glycoprotein specific for the target antibody by the target antibody present in the sample. In a typical example of such an assay, the engineered glycoprotein is immobilized and the exogenous target antibody is labeled. Since the amount of the exogenous target antibody bound to the glycoprotein is inversely proportional to the concentration of the target antibody present in the sample, the target antibody level in the sample can thus be determined based on the amount of exogenous target antibody bound to the glycoprotein and, thus, immobilized.
As would be readily appreciated by a worker skilled in the art, other assay formats can be used that fall within the present immunoassay provided that they can take advantage of the formation of binding complexes between the present engineered glycoprotein and a target antibody to identify or quantify bacterial infection.
The immunoassays described herein typically utilize a labeling agent to specifically bind to and label the binding complex formed by the target antibody and the engineered glycoprotein. The labeling agent may itself be one of the moieties comprising the antibody/glycoprotein complex, or may be a third moiety, such as another antibody, that specifically binds to the antibody/glycoprotein complex. A label may be detectable by, for example, spectroscopic, photochemical, biochemical, immunochemical, electrical, optical or chemical means. Examples include, but are not limited to, fluorescent dyes (e.g., fluorescein isothiocyanate, Texas red, rhodamine, and the like), radiolabels (e.g., 3H, 125I, 35S, 14C, or 32P), enzymes (e.g., horse radish peroxidase, alkaline phosphatase, and others commonly used in an ELISA), luminescent dyes, and colorimetric labels such as colloidal gold or colored glass or plastic (e.g., polystyrene, polypropylene, latex, etc.) beads.
In some cases, the labeling agent is a secondary antibody bearing a detectable label. Alternatively, the secondary antibody may lack a label, but it may, in turn, be bound by a labeled third antibody specific to antibodies of the species to which the secondary antibody corresponds. Alternatively, the secondary antibody can be modified with a detectable moiety, such as biotin, to which a third labeled molecule can specifically bind, such as enzyme-labeled streptavidin.
Other proteins capable of specifically binding immunoglobulin constant regions, such as protein A or protein G, can also be used as the label agents. These proteins are normal constituents of the cell walls of streptococcal bacteria. They exhibit a strong non-immunogenic reactivity with immunoglobulin constant regions from a variety of species (see, generally, Kronval, et al. J. Immunol., 111: 1401-1406 (1973); and Akerstrom, et al., J. Immunol., 135: 2589-2542 (1985)).
As noted above, the immunoassay optionally includes the use of immobilized engineered glycoprotein. In this embodiment, the engineered glycoprotein is bound directly to a solid support, which may be, for example, the surface of microtitre plates, polymer beads, agarose beads, paramagnetic (or magnetic) beads, or membranes. The engineered glycoproteins can be immobilized on the surface of the solid support by various means. In one embodiment, the glycoconjugates are covalently bound to the solid support. For example, the surface of the solid support can be surface modified to include any typical modifying group, such as a carboxyl group, that reacts with the amino groups (—NH2) of the protein in the engineered glycoprotein. In a specific, non-limiting example, the engineered glycoproteins can be covalently bound to a solid surface that is surface-modified with carboxyl group, by a one step reaction is performed using 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide hydrochloride as a catalyzer.
In accordance with another aspect there is a provided an immunoassay kit comprising engineered glycoproteins as described above and reagents for the detection of binding complexes formed with the engineered glycoproteins and antibodies specific for bacterial antigens corresponding with the antigenic components of engineered glycoproteins. The immunoassay kit can additionally include instructions for use and/or a container or other means for collecting a sample of bodily fluid from a subject suspected of having a bacterial infection.
To gain a better understanding of the invention described herein, the following examples are set forth. It should be understood that these examples are for illustrative purposes only. Therefore, they should not limit the scope of this invention in any way.
The assay described herein is based on antigen-antibody interaction, as are all immunoassays. In the embodiment of this example, engineered glycoproteins are covalently linked to paramagnetic surface-modified microbeads.
In use, a typical assay in accordance with the present embodiment is summarized as follows:
1) the modified microparticles are incubated with serum to be analyzed;
2) the serum-incubated microparticles are then washed and incubated with secondary antibodies, which are conjugated with a reporter molecule, such as peroxidase or Cy5; and
3) the serum-incubated microparticles from 2) are washed again and developed either by, for example, fluorescence (Cy5) or electrochemically (peroxidase).
A schematic representation of this exemplary assay is shown in
Briefly, a dilution of the serum to be assayed (1:100 to 1:500 depending on the sample and the antigen used) is incubated for 5 min with the nanobeads coated with a engineered glycoprotein. After this incubation, the microbeads are pelleted with a magnetic field; washed; and resuspended in the presence of the secondary antibody and incubated for 5 min. The beads are pelleted again with a magnetic field, washed three times with buffer PBS and either measured directly in a spectrofluorometer if a Cy5 secondary antibody is used or incubated with oxygen peroxide and measured electrochemically if a secondary conjugated to peroxidase is used.
The enterohemorragic Escherichia coli O157 is a common foodborne pathogen associated with the hemolytic uremic syndrome (HUS), with a high mortality rate, especially among children under 5 years old. The disease is preceded by an episode of diarrhea, usually with the presence of blood. To date there is no rapid and robust test to diagnose this important human pathogen in the acute phase of the diarrhea.
To assay for E. coli O157, the AcrA-AO157 engineered glycoprotein antigen was coupled to magnetic microbeads. The AcrA-AO157 glycoprotein includes the AcrA protein of C. jejuni coupled to an E. coli glycan using a PTase. This immune test was used to detect an E. coli O157 infection as early as 2 days post-bloody diarrhea. As shown in
Brucella spp. is the etiological agent of Brucellosis, a wide spread zoonosis that affects a broad range of mammals, including humans. Brucella abortus infects bovines and causes abortion in pregnant animals inflicting significant economic losses in developing countries, in some of which it is still endemic. Although there are many diagnostic assays for cattle and humans known, it is often necessary to run several of them in parallel to have a confirmed diagnosis. This can be a complicated and expensive exercise.
A novel engineered glycoprotein, AcrA-AO9, was constructed, which has the AcrA protein of C. jejuni coupled to the O-antigen of Yersinia pseudotuberculosis O9 (which has the same structure than the Brucella O-antigen). Synthesis of this engineered glycoprotein is described previously (Feldman et al., supra). This antigen was coupled to paramagnetic microbeads and tested with sera of vaccinated and infected cows, as well as with sera of humans with acute or chronic Brucellosis.
To demonstrate that the immunoassay of the present example is suitable to diagnose human Brucellosis, sera from 4 confirmed human infections and one knee synovial fluid product of a Brucella abortus abscess were analyzed. As shown in
Brucellosis commonly infects humans and can cause severe symptoms such as sweating, fatigue, anorexia, weight loss, headache, arthralgia and generalized aching. In severe cases, Brucellosis can cause abscesses, endocarditis and neurobrucellosis, sometimes leading to death. Early detection in humans would be very helpful in decreasing the severity and prevalence of the disease in human populations.
An indirect immunoassay was developed to detect antibodies against “smooth” Brucella spp. using as an antigen a recombinant O-polysaccharide-protein conjugate (AcrA-OAg) coupled to magnetic beads. AcrA-OAg was produced in Escherichia coli by co-expressing PglB, a Campylobacter jejuni oligosaccharyltransferase, the gene cluster encoding the enzymes required for the synthesis of Brucella abortus O-polysaccharide and the protein acceptor AcrA. Introduction of PglB in E. coli results in the transfer of B. abortus O-polysaccharide from its carrier to AcrA. The AcrA-OAg glycoprotein, expressed as an histidine-tag fusion protein, can then be purified from E. coli fermentations without the need for culturing the pathogenic bacteria. AcrA-OAg was purified in one-step by affinity chromatography and immobilized on carboxy-modified magnetic beads. Functionalized micro-beads were incubated with the samples and the immune complexes were detected using anti-human or anti-bovine IgM/G Cy5 conjugate antibodies.
Glycoconjugate Detection Compared to Standard Serological Tests for Brucella
The use of the AcrA-OAg glycoconjugate as an antigen for the diagnosis of human brucellosis was evaluated. A glycoconjugate magnetic bead-based immunoassay was carried out for the detection of antibodies against the Brucella abortus O-antigen. In brief, magnetic beads coated with the AcrA-OAg glycoconjugate were incubated with the indicated human serum samples (dilution 1/100). Bound antibodies were detected using goat anti-human IgG Cy5-conjugated antibodies. The results are expressed as percentage of reactivity of the positive control serum.
Standard serological tests for Brucella were also carried out on culture-positive patients. As shown in Table I, the results of the magnetic bead assay are compared with standard laboratory tests such as SAT (serum agglutination test), TAT (tube agglutinin test), TAT-2ME (2-mercapto-ethanol tube agglutination test) and CFT (complement fixation test) are shown as titers. For the RBT (Rose-Bengal test) and BPAT (buffered antigen plate agglutination test), the results are indicated as positive (POS) or negative (NEG). The cutoff value for cELISA (competitive enzyme-linked immunosorbent assay) is 28%. As is evident from the table, the results of standard or known diagnostic laboratory assays for Brucella sp. varies widely, and can give false negative results in some instances.
The results for the magnetic bead assay are expressed as percentage of reactivity of the control positive serum. The notation ‘ND’ means that the result was not determined. The cutoff for the magnetic bead based assays is 13-14%. Above this percent, the result is considered positive.
Brucella sp.
B. suis bv 1
B. suis bv 1
B. suis bv 1
B. abortus bv 1
B. melitensis bv 1
B. abortus bv 1
B. suis bv 1
B. abortus
B. abortus bv 1
B. abortus bv 2
B. suis bv 1
B. abortus bv 1
B. abortus bv 1
B. suis bv 1
B. abortus bv 1
B. melitensis
B. melitensis
B. melitensis
B. melitensis
B. melitensis
B. melitensis
B. melitensis
B. melitensis
B. melitensis
B. melitensis
The bar graph data shown in
Detection of Brucella in Human Sera Samples
Samples of human serum were tested to determine the presence of Brucella. Serum samples were obtained from 413 individuals, including healthy individuals and patients from each of the following different clinical groups:
(i) Culture-positive brucellosis patients: A total of 25 sera were obtained from patients with positive blood cultures for Brucella abortus, Brucella melitensis and Brucella suis (see Table I).
(ii) Culture-negative, serologically-positive patients with clinical diagnosis of brucellosis: A total of 52 sera were obtained from patients with clinical symptoms compatible with brucellosis and with positive RBT, BPAT, SAT (Huddleson), TAT (Wright), TAT-2ME (2-mercaptoethanol), CELISA and CFT results at any titer.
(iii) Blood donors: A total of 240 sera were obtained from healthy individuals with no clinical or epidemiological evidence of brucellosis (18 to 65 years old) and with negative BPAT and SAT (Huddleson) results.
(iv) Patients with a febrile syndrome: A total of 34 serum samples were obtained from patients who initially had a clinical suspicion of brucellosis but had a different final diagnosis. These samples were negative by all the serological diagnostic tests (RBT, BPAT, SAT, TAT, TAT-2ME, cELISA and CFT).
(v) Healthy individuals occupationally-exposed to the pathogen: A total of 30 sera were obtained from research and clinical laboratory workers, and cattle ranchers.
(vi) Patients with other bacterial infections or with autoimmune pathologies: A total of 32 sera were obtained from patients infected with Mycobacterium tuberculosis, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Streptococcus pneumoniae and Staphylococcus aureus, and with autoimmune pathologies such as rheumatoid arthritis, systemic lupus erythematosus and autoinmune vasculitis.
Glycoconjugate magnetic bead assay analyses of serum samples were obtained from healthy individuals and patients from different clinical groups. The results of these assays are shown in
A further receiver-operating characteristic (ROC) analysis was carried out using a glycoconjugate magnetic bead assay. The results of this assay are shown in
The sensitivity, specificity, and likelihood ratios of the test were calculated for different cutoff values. The results of these calculations are shown in Table 2. The values in parentheses as a percentage sensitivity and percentage specificity indicate the 95% confidential interval. The reported ‘LR’ is the likelihood ratio. Specifically, the Positive LR was calculated as sensitivity/(1.0-specificity) and the Negative LR as (1.0-sensitivity)/specificity.
The relationship between the test outcome and the presence or absence of disease is shown in Table 3. The ‘positive’ category includes culture-positive brucellosis patients (25 sera) and culture-negative, serological-positive patients with clinical diagnosis of brucellosis (52 sera). The ‘negative’ category includes blood donors (240 sera), patients with a febrile syndrome (34 serum samples), healthy individuals occupational-exposed to the pathogen (30 sera) and patients with other bacterial infections or with autoimmune pathologies (32 sera). The following acronyms are used in the table: TP, true positive; TN, true negative; FN, false negative; FP, false positive; Se, sensitivity; Sp, specificity; PPV, positive predictive value (TP/TP+FP) and NPV (TN/TN+FN), negative predictive value. A cutoff value of 13.2% was taken as indicative of brucella.
Serum, whole blood and milk samples were obtained from a vaccination/infection trial. Samples were collected from the following animal groups:
Three different samples were obtained for each animal in the trial: a pre-infection sample, a sample obtained 21 days after infection and finally a sample obtained 6 months post-infection. A similar assay was performed using the AcrA-OAg glycoconjugate as described in Example 4.
In all the cases, reactivity was only observed in the samples obtained at 180 days (6 months) post-infection. This demonstrates that the present assay can differentiate infected from non-infected animals. The results of this trial are shown in
To evaluate the specificity of the reaction, a Western blot analysis was performed using the same bovine samples analyzed above. The results of this assay are shown in
Animals experimentally vaccinated with S19 were challenged with wild type B. abortus 2308. In parallel analysis, serum and whole blood samples were obtained and tested 6 months post-infection. The results of this assay are shown in
Analysis of serum samples from animals experimentally vaccinated with the smooth vaccine strain S19, was performed using the presently described AcrA-OAg assay. (The S19 vaccine strain is described in: Arenas-Gamboa A. M. et al. Infect Immun. 2009, 77(2):877-84; Crasta O. R. et al. PLoS ONE, 2008, 3(5):1-13; and Klesius P. H. et al. American Journal of Veterinary Research 1978, 39(5):883-886, all incorporated by reference herein.) Six samples were analyzed for each animal: a pre-vaccination sample, a sample obtained 30 days post-vaccination, samples obtained 395, 520 and 630 days post-vaccination and a sample obtained 21 days post-challenge with a virulent smooth strain. In all the analyzed animals, we have detected reactivity against the antigen at 30 days post-vaccination that then decreased at negative levels. The results of this study are graphically shown in
Animals experimentally vaccinated with S19 were challenged with wild type B. abortus 2308. In parallel, analysis of serum and milk samples from animals experimentally vaccinated with the smooth vaccine strain S19 was performed. Milk and serum samples were obtained post-delivery or post-abortion at 60 or 90 days post-challenge. The results of this study are shown in
Analysis was also performed using serum samples from animals experimentally vaccinated with the rough vaccine strain Δpgm. (Ugalde J. E. et al. Infect Immun. 2003,71(11): 6264-6269, incorporated by reference herein). Six samples were analyzed for each animal: a pre-vaccination sample; a sample obtained 30 days post-first vaccination; a sample obtained pre-second vaccination; samples obtained 30 and 150 days post-second vaccination; and a sample obtained 21 days post-challenge with a virulent smooth strain. The results of this trial are shown in
All publications, patents and patent applications mentioned in this Specification are indicative of the level of skill of those skilled in the art to which this invention pertains and are herein incorporated by reference to the same extent as if each individual publication, patent, or patent applications was specifically and individually indicated to be incorporated by reference.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
This application is a continuation of U.S. application Ser. No. 14/238,451, filed Jul. 24, 2014, which is a U.S. National Stage application, under 35 U.S.C. 371, of PCT/CA2012/050549, filed in English on Aug. 13, 2012, which claims priority from U.S. Provisional Application No. 61522967, filed on Aug. 12, 2011. Each of these applications is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61522967 | Aug 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14238451 | Jul 2014 | US |
| Child | 15632581 | US |
