Production of Yersinia stable toxin (YST) and distribution of yst genes in biotype 1A strains of Yersinia enterocolitica

Two hundred and fifty nine isolates of Yersinia enterocolitica and related species were examined for the production of heat-stable enterotoxin (Yersinia stable toxin; YST) as well as for the prevalence of enterotoxin genes, viz. ystA, ystB and ystC. Under the conventional conditions used for the production of Y. enterocolitica enterotoxin, i.e. in tryptic soy broth (TSB) supplemented with yeast extract at 28degreesC for 48 h, 77.7% of clinical isolates and 62.3% of swine isolates showed enterotoxigenicity in infant mice. All isolates that produced enterotoxin at 28degreesC also showed enterotoxic activity at 37degreesC after 48 h incubation under an alkaline pH of 7.5, the pH present in the ileum. All Yersinia intermedia and Yersinia frederiksenii isolates were negative for enterotoxin production. All clinical isolates and 96.3% of Y. enterocolitica isolates from swine hybridized with a probe for ystB, which indicated that the ystB gene was most prevalent in Y. enterocolitica biotype 1A strains. None of the Y. enterocolitica isolates showed hybridization with oligonucleoticle probes for ystA or ystC. The study indicated that YST-b was the major contributor to diarrhoea produced by biotype 1A strains of Y. enterocolitica.