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Clostridium difficile Toxins A and B, Molecular Detection

Clostridium difficile, the main etiological agent of antibiotic-associated diarrhea and pseudomembranous colitis, is also the major cause of nosocomial diarrhea. The use of antibiotics such as clindamycin, cephalosporins, and ampicillin disrupts the normal intestinal flora (intestinal microbiome), predisposing patients to colonization by C. difficile, which is encountered mainly in healthcare centers.

This microorganism is carried asymptomatically in about 50% of neonates and 20% of hospitalized patients but only in 2% of healthy adults. In fact, asymptomatic carriers usually outnumber symptomatic patients. Therefore, the high level of healthy carriers among hospitalized patients coupled with the presence of patients under antibiotic treatment explains the high rate of nosocomial diarrhea associated with C. difficile.

The pathogenicity of this organism is associated with the production of two toxins, toxin A (TcdA) and toxin B (TcdB), both implicated in mucosal damage. Nontoxigenic strains are not pathogenic. Most strains produce both toxins, but pathogenic strains of C. difficile producing toxin B only have been reported.

The detection of toxin B by the tissue culture cytotoxicity assay is the “gold standard” for the detection of C. difficile from fecal samples. This assay is efficient but still requires 24 to 48 h for completion while it can only be carried out in very large and properly equipped reference laboratories. Enzyme immunoassays (EIA) and immunochromatographic tests are also used for toxin detection. However, these assays are not as sensitive as the cytotoxicity assay.

Molecular testing using real-time PCR for the rapid detection of all toxigenic C. difficile strains directly from feces samples is a simple, rapid, and specific diagnostic test that would be helpful to the clinician for the administration of an efficient treatment at the beginning of the infection to avoid complications.

This assay is based on the amplification of the genes encoding toxins A and B, the major virulence factors of this bacterial species.

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