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  • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
  • C12Q1/68—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving nucleic acids
  • C12Q1/6876—Nucleic acid products used in the analysis of nucleic acids, e.g. primers or probes
  • C12Q1/6888—Nucleic acid products used in the analysis of nucleic acids, e.g. primers or probes for detection or identification of organisms
  • C12Q1/689—Nucleic acid products used in the analysis of nucleic acids, e.g. primers or probes for detection or identification of organisms for bacteria
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
  • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
  • G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
  • G01N33/569—Immunoassay; Biospecific binding assay; Materials therefor for microorganisms, e.g. protozoa, bacteria, viruses
  • G01N33/56911—Bacteria
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2333/00—Assays involving biological materials from specific organisms or of a specific nature
  • G01N2333/195—Assays involving biological materials from specific organisms or of a specific nature from bacteria
  • G01N2333/33—Assays involving biological materials from specific organisms or of a specific nature from bacteria from Clostridium (G)

Definitions

• Clostridium difficile (C. difficile) is the most common known cause of nosocomial diarrhea and accounts for about 3 million cases of diarrhea annually in the United States.
• the risk factors of C. difficile infection (CDI) include exposure to antibiotics, advanced age, and residence in hospitals or long-term care facilities.
• the symptoms of CDI range from mild diarrhea to pseudomembranous colitis and toxic megacolon.
• the average cost of treatment is about $10,000 per case.
• the mortality rate of CDI increased from 5.7 deaths per million population in 1999 to 23.7 deaths per million population in 2004 due to the emergence of hypervirulent outbreak strains.
• the ribotype 027 strain contributed significantly to the increased CDI incidence.
• the accurate differentiation of the outbreak strain ribotype 027 from other strains of C. difficile can facilitate decision making for treatment options.
• FIG. 1 depicts a comparison between anti-CwpV ELISA and PCR ribotyping methods, according to embodiments of the invention
• FIG. 2 depicts that antibodies generated against the 027-specific region of
• FIG. 3 depicts interpretation of the results of Anti-CwpV QUIK CHEK®.
• FIG. 4 depicts a comparison between anti-CwpV QUIK CHEK® and PCR ribotyping methods, according to embodiments of the invention. DETAILED DESCRIPTION OF THE INVENTION
• Embodiments of the present invention are directed to test methods for differentiating C. difficile strains in patients based on the presence of a ribotype-specific new antigen marker, Cell Wall Protein V (CwpV).
• Ribotype specific CwpV may be used in an immunoassay for the detection of C. difficile ribotypes, especially the outbreak strain 027.
• anti-strain specific CwpV antibodies are used in immunoassays for highly sensitive identification of C. difficile strain 027.
• PCR ribotyping is relatively easy to perform, reproducible, and is one of the most discriminatory methods to differentiate C. difficile strains.
• the frameshift mutation may cause an increase of toxin production.
• the historical 027 strains isolated in France in 1988 were susceptible to fluoroquinolones and erythromycin but the mutations in gyrA/B and the 23 s RNA genes rendered ribotype 027 in recent outbreaks resistance to both antibiotics.
• the altered surface proteins with higher affinity to human intestinal epithelial cells may also contribute to the enhanced virulence.
• the traditional antibiotics of choice for the treatment of CDI are metronidazole and vancomycin.
• metronidazole and vancomycin are equally effective.
• vancomycin produced better outcomes.
• a high relapse rate was observed in patients treated with either metronidazole or vancomycin.
• a new drug named Fidaxomicin (Dificid; Optimer Pharmaceuticals) was approved by the U.S. Food and Drug Administration (FDA) for the treatment of C. difficile-associated diarrhea in adults.
• Fidaxomicin is a narrow spectrum antibiotic against gram-positive anaerobes.
• Fidaxomicin Resistance to fidaxomicin was found in Bacteroides spp., aerobic and facultative gram- negative bacilli and anaerobic gram-negative bacilli. Fidaxomicin is equally effective against 027 and non-027 strains of C. difficile. The use of broad-spectrum antibiotics disturbs the gut flora which may contribute to the relapse of C. difficile infection. Recent studies indicate that fidaxomicin treatment resulted in lower relapse rate in patients infected by non-027 strains in comparison to vancomycin treatment. Therefore the differentiation between 027 and non-027 strains may facilitate the decision making of the physicians in terms of treatment options.
• the PCR ribotyping method requires the isolation of C. difficile colonies
• Commercially available molecular tests utilize the sequence variation in the tcdC gene.
• the PCR based tests are expensive and non-specific because the mutations in tcdC gene are also present in other ribotypes.
• Antibody-based tests such as Enzyme-linked immunosorbent assays (ELISAs) and lateral flow assays, are rapid and cost-effective tests for the detection of pathogen-specific antigens.
• 027 strain specific antigen(s) are used as a diagnostic marker(s) for the detection of 027 strains in immunoassays.
• C. difficile cells possess a surface layer (S-layer) outside of the peptidoglycan layer.
• S-layer is present in both vegetative cells and C. difficile spores. Proteins within the S-layer mediate host-pathogen interactions. Several C. difficile surface proteins bind to gastrointestinal tissues and are potential colonization factors.
• the proteins associated with the S-layer contain two domains: a conserved cell wall binding domain and a variable domain that specifies the function of that particular protein. Twenty-eight cell wall proteins (CWPs) are predicted in the genome of the sequenced strain 630. The variable domains of certain CWPs are considered potential antigen markers for C. difficile strain identification.
• CWPs Twenty-eight cell wall proteins
• CwpV (CD0514) is a member of the CWPs and consists of an N-terminal region with a putative cell wall binding domain and a C-terminal domain which may promote aggregation.
• CwpV is secreted into culture medium by various 027 strains.
• the C-terminal domain of CwpV is highly variable among C. difficile ribotypes.
• the specific amino acid sequences of the C-terminal repeats found in the CwpV protein in ribotype 027 are not represented in the genome of any other sequenced strains to date.
• the ribotype- specific region of CwpV can be used as a diagnostic marker for the 027 strains.
• a ribotype 027-specific C-terminal peptide of CwpV was expressed in E. coli using recombinant DNA techniques. Polyclonal antibodies against the recombinant CwpV were generated in goats. An ELISA was developed using polyclonal anti-CwpV antibodies as capturing antibodies and horseradish peroxidase (HRP)-conjugated polyclonal anti-CwpV antibodies as detection antibodies.
• HRP horseradish peroxidase
• the results of anti-CwpV ELISA on 72 human fecal samples were compared to the results of PCR ribotyping method.
• Anti-CwpV ELISA detected the presence of C. difficile 027 strain in 30 of the 35 027-positive samples determined by the PCR ribotyping method.
• the sensitivity and specificity of the anti-CwpV ELISA are each 86%.
• a ribotype 027-specific C-terminal peptide of CwpV was expressed in E. coli. Polyclonal antibodies against the recombinant CwpV were generated in goats. An ELISA was developed using polyclonal anti-CwpV antibodies as capturing antibodies and horseradish peroxidase (HRP)-conjugated polyclonal anti-CwpV antibodies as detection antibodies.
• HRP horseradish peroxidase
• C. difficile strains were inoculated into Brain-heart infusion broth (BHI; Oxoid). Cultures were grown at 37°C overnight under anaerobic conditions. The C. difficile strains in BHI cultures were diluted 1:20 in phosphate buffered saline (PBS) and tested on the ELISA described above.
• BHI Brain-heart infusion broth
• PBS phosphate buffered saline
• a ribotype 027-specific C-terminal peptide of CwpV was expressed in E. coli.
• Polyclonal antibodies against the recombinant CwpV were generated in goats.
• a QUIK CHEK® device was developed using polyclonal anti-CwpV antibodies immobilized as the test line on microfiber glass membrane as capturing antibodies and horseradish peroxidase (HRP)-conjugated polyclonal anti-CwpV antibodies as detection antibodies.
• HRP horseradish peroxidase
• a positive result on anti-CwpV QUIK CHEK® is indicated by two blue lines: the control line ("C") and the test line ("T").
• a negative result on anti-CwpV QUIK CHEK® is indicated by a single blue line on the control ("C") side of the reaction window with no test line visible on the "T” side of the reaction window. The result is interpreted invalid when no control line ("C") is visible.
• embodiments of the present invention provide CwpV as a diagnostic marker for detecting C. difficile ribotype 027 in stool samples and in cultures.
• the present invention has been described in relation to particular embodiments which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its scope.

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• 2013
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