Usefulness of a combination of pulsed-field gel electrophoresis and enrichment culture in laboratory investigation of a foodborne outbreak due to Clostridium perfringens.

Clostridium perfringens is ubiquitous in nature and normally detectable in human stools. Therefore, it is difficult to perform specific microbiologic diagnosis in foodborne outbreaks, particularly when only a few cultures are detected from fecal specimens. Usually, it has been necessary to detect over 10(6) spores/g of fecal sample as a diagnostic criterion of diarrhea due to C. perfringens. A relatively large foodborne outbreak occurred in Osaka City, Japan in October 2001. Although C. perfringens was suspected as the causal agent, four to seven days had passed after the onset of symptoms before fecal specimens were brought into our laboratory. The positive rate obtained by direct plating was quite low (13/83). We attempted to detect the organisms using enrichment culture after 75 degrees C 20 min heat-treatment, and C. perfringens enterotoxin gene (cpe)-positive strains were isolated from 53 of 81 samples. Pulsed-field gel electrophoresis (PFGE) and serotyping showed that 36 (67.9%) of these 53 strains had indistinguishable PFGE patterns and the same serotype, TW69. Our experience indicates that the enrichment culture could be useful for laboratory confirmation of a C. perfringens foodborne outbreak if it is used with adequate molecular epidemiologic methods.