[Evaluation of four rapid methods for the investigation of the toxigenic capacity of Clostridium difficile strains isolated in a selective medium].

BACKGROUND: Use of selective Clostridium difficile culture as a diagnostic method for C. difficile associated disease requires to prove the toxigenic ability of the isolates. Toxin B detection by cell culture assay after growing the microorganism in enriched broth is the standard method, but it delays the final diagnosis for 3-5 days. This study compares retrospectively four rapid techniques for detecting these toxigenic C. difficile strains. METHODS: 106 clinical isolates of C. difficile (72 toxigenic and 34 non-toxigenic), these and 16 clinical strains of other species of Clostridium were investigated. The four methods were performed directly from colonies growing on solid agar. They were: a) cytotoxin detection in cell culture; b) two PCR amplifications of toxin A and toxin B, respectively, and c) toxin A detection by an immunoenzymatic method (VIDAS CDA2). All these procedures were completed within a normal working day. RESULTS: Only the 72 toxigenic C. difficile strains gave positive results by cell culture and PCR techniques (sensitivity and specificity: 100%). A total of 14 out of 49 toxigenic C. difficile strains showed negative results by the VIDAS assay in the first run, but all them were positive in repeated tests. CONCLUSIONS: Although all methods performed well, the cytotoxicity assay done directly on colonies growing in CCFA is a simple and rapid technique, and appears to be well-suited for use in laboratories with access to cell cultures.