Plasmid profiling for strain differentiation and characterization of Clostridium perfringens isolates.

Plasmid profiling was used for the characterization of 13 Clostridium perfringens collection strains as well as 85 clinical and food isolates. Methodological details and limitations of the plasmid isolation procedure are outlined and discussed. For 19 clinical isolates obtained during seven group outbreaks, a close connection between at least some strains from each individual outbreak was established for six of them; only results from one outbreak were completely inconclusive, due to missing plasmids in one of the two isolates. The presence of multiple plasmid types within seven out of 12 given food samples, from which at least two C. perfringens isolates were obtained, indicates the importance of multiple isolates for meaningful typing results in epidemiological investigations. By including results from a previous report from this laboratory, baseline data on plasmid profiles for a total of 133 isolates are provided. The results of this study revealed that 36% of the food isolates unrelated to disease outbreaks carried no plasmids, as compared with 19-25% among disease-related isolates. A high prevalence (24.8%) of a 8.9 +/- 0.5 MDa plasmid was found among the 133 isolates, which contributed to one of four occurrences of identical plasmid profiles among strains that were initially considered unrelated. Two of these identical plasmid profiles were found among strains from the same culture collection, indicating the possibility of a common ancestor strain or cross-contamination.