Detection of Yersinia enterocolitica heat-stable enterotoxin by suckling mouse bioassay

Distribution of the ymoA and ystA genes and enterotoxins yst production by Yersinia enterocolitica strains isolated from humans and pigs

Yersinia (Y.) enterocolitica is the third etiological agent of human diarrhea in terms of the number of confirmed clinical cases. One of the important virulence markers is the yst gene which encodes the production of enterotoxins Yst (Yersinia stable toxins). However, not all strains with yst genes produce enterotoxins, what seems to be caused by the ymoA gene encoding the production of the YmoA protein inhibiting the expression of various genes. The purpose of our study was to evaluate the distribution of the ymoA and ystA genes and Yst production by Y. enterocolitica isolated from humans and pigs. All the studied strains obtained from pigs had the ystA gene which indicates that they belong to the group of strains commonly regarded as pathogenic, but the ability to produce YstA was detected in only 14 out of 96 examined strains. The fragments of ystA gene were also detected in all Y. enterocolitica strains isolated from human cases of diarrhea. Amplification of a fragment of the ymoA gene was detected in all the studied strains, both from humans and pigs, based on the presence of a 330 bp band. Thus no correlation was identified between the occurrence of the ymoA and ystA genes and the production of a specific type of enterotoxin.

Characteristics of Yersinia intermedia-like bacteria isolated from patients with diarrhea in Nigeria

Five Yersinia strains, biochemically mimicking Yersinia intermedia, were isolated from patients with acute diarrheal diseases seen at the University of Lagos (Nigeria) Teaching Hospital between October 1979 and September 1982. The five isolates utilized citrate as their source of carbon and fermented sucrose, L-rhamnose, and alpha-methyl-D-glucoside, but unlike any other Y. intermedia biogroup, they failed to ferment D-melibiose or D-raffinose. They all belonged to serogroup O:52,53. Four autoagglutinated and were calcium dependent for growth at 37 degrees C. Three caused conjunctivitis in the guinea pig eye model, but none possessed the 42-megadalton virulence plasmid. Four of the isolates caused diarrhea in orally infected mice and rabbits but were nonlethal for these animals. These results suggest that these isolates represent yet another Yersinia species with disease-producing capabilities in humans.

Factors affecting detection of Yersinia enterocolitica heat-stable enterotoxin by the infant mouse test

With regard to the assay of heat-stable enterotoxin (ST) from Yersinia enterocolitica, we made a comparative study of the conventional infant mouse test read at 4 h and a modified infant mouse test read at 2 h. The influence of several factors, such as the medium used to prepare ST, lysing of bacterial cells from the broth cultures used to prepare ST, and the temperature at which the inoculated mice were kept during the test, was also investigated. Thus, with a few exceptions, Pai-Mors medium was more suitable than Casamino Acids-yeast extract medium, for the preparation of yersinial ST. Gut/carcass weight ratios obtained with lysed supernatants or with supernatants from whole cultures of Y. enterocolitica were similar, suggesting that most of the ST produced by this microorganism in broth cultures is extracellular. The amount of ST produced by Y. enterocolitica, as well as the ambient temperature at which inoculated mice were kept during the assay, was found to influence gut/carcass weight ratios obtained with both tests. Enterotoxigenicity and the temperature at which mice were kept were interrelated, such that for weakly enterotoxigenic strains there were no significant differences among gut/carcass weight ratios for the conventional and modified infant mouse tests carried out at 18 or 25 degrees C, but at 30 degrees C the values in the modified test were higher for most ST preparations with Pai-Mors medium. The influence of ambient temperature was more pronounced at 37 degrees C, since most strains produced negative results in the conventional test at this temperature. We conclude that the conventional infant mouse test is adequate for assaying yersinial ST, provided that the temperature at which mice are kept during the assay is fixed at around 25 degrees C.

Enterotoxin production in milk at 22 and 4 degrees C by Escherichia coli and Yersinia enterocolitica

Enterotoxigenic Escherichia coli (five strains) and Yersinia enterocolitica (five strains) were cultivated in sterile milk at 22 and 4 degrees C. The bacteria grew well at both temperatures. Three strains of E. coli produced heat-labile enterotoxin in the milk at 22 degrees C as demonstrated by enzyme-linked immunosorbent assay. Heat-stable enterotoxins were not detected in milk by the infant mouse test.