Genotyping of outbreak-related and sporadic isolates of Clostridium difficile belonging to serogroup C

Serogroup C of Clostridium difficile is the serogroup most frequently related to outbreaks. Fifty-six toxigenic serogroup C isolates of C. difficile were genotyped by ribotyping PCR (ribo-PCR), random amplified polymorphic DNA (RAPD) assay, and pulsed-field gel electrophoresis (PFGE). Thirty-five of the 56 isolates were recovered from four unrelated outbreaks (Belgium, 1987, 1992, and 1995; France, 1992 to 1993), 7 derived from a spatiotemporal cluster in Cotonou, Benin (1992), and 14 were sporadic isolates. The serogroup C reference strain, also isolated during an outbreak (Belgium, 1983), was genotyped too. Ribo-PCR, the RAPD assay, and PFGE generated 2, 5, and 11 major genotypes, respectively. Combination of the three methods finally yielded 13 general types, although ribo-PCR did not play any role in enhancing resolution. Three general types were recovered from all the isolates from the five outbreaks and the cluster, with two types being predominant. The 14 sporadic serogroup C isolates were divided into 11 overall genotypes. These results indicate that genotyping methods, and more particularly the combination of the RAPD assay and PFGE, can resolve genetic diversity within toxigenic, serogroup C C. difficile strains. Also, this study suggests that outbreak-related serogroup C strains are limited to a few genetically stable and apparently very widely (internationally and intercontinentally) distributed genotypes.