Pathogenicity tests with strains of Edwardsiella tarda: detection of a heat-stable enterotoxin.

A total of 25 strains of Edwardsiella tarda isolated from various sources in different parts of the world between 1968 and 1982 was subjected to enteropathogenicity tests. A heat-stable enterotoxin was detected in three strains (12%). Whereas culture filtrates gave doubtful results, concentration of toxin by ultrafiltration led to net fluid accumulation in the suckling mouse test and the rabbit ligated ileal loop assay. The enterotoxin resisted heating to 60 degrees C (30 min) and 100 degrees C (15 min). Neither cell elongation nor cytotoxic effect were observed in the Chinese hamster ovary cell assay. No strain caused keratoconjunctivitis in the guinea pig eye model. There was no correlation of enterotoxigenic strains and a typical pathology. With regard to the usual clinical pattern of E. tarda enteritis, which primarily appears to be invasive, it is suggested that enterotoxin production might be of secondary pathogenetical importance, comparable to toxin production in salmonellosis, shigellosis, and Yersinia enterocolitica infection.