ASSOCIATION OF ENTEROHEMORRHAGIC ESCHERICHIA-COLI HEMOLYSIN WITH SEROTYPES OF SHIGA-LIKE-TOXIN-PRODUCING ESCHERICHIA-COLI OF HUMAN AND BOVINE ORIGINS

In this study we investigated whether the enterohemorrhagic Escherichi a coil (EHEC) hemolysin gene ehxA could be used as an indicator of pat hogenicity in Shiga-like-toxin-producing Escherichia coil (SLTEC) isol ates. The isolates in a collection of 770 SLTEC strains of human and b ovine origins,were assigned to group 1 (230 human and 138 bovine SLTEC isolates belonging to serotypes frequently implicated in human diseas e), group 2 (85 human and 183 bovine isolates belonging to serotypes l ess frequently implicated in disease), and group 3 (134 bovine isolate s belonging to serotypes not implicated in disease). PCR amplification was used to examine all of the SLTEC isolates for the presence of ehx A. and the virulence-associated genes eae, sit-I, and sit-II. The perc entages of human isolates in groups 1 and 2 that mere positive for ehx A were 89 and 46%, respectively, and the percentages of bovine isolate s in groups 1 to 3 that were positive for ehxA were 89, 51, and 52%, r espectively. The percentages of human isolates in groups 1 and 2 that were positive for eae were 92 and 27%, respectively, and the percentag es of bovine isolates in groups 1 to 3 that mere positive for eae were 78, 15, and 19%, respectively. The frequencies of both ehxA. and eae were significantly higher for group 1 isolates than for group 2 isolat es. The presence of the ehxA gene was associated with serotype, as was the presence of the eae gene. Some serotypes, such as O117:H4, lacked both eae and ehxA and have been associated with severe disease, but o nly infrequently. The sit-I genes were more frequent in group 1 isolat es than in group 2 isolates, and the sit-II genes were more frequent i n group 2 isolates than in group 1 isolates. In a second experiment,pe determined the occurrence of the ehxA and sit genes in E. coil isolat ed from bovine feces. Fecal samples from 175 animals were streaked ont o washed sheep erythrocyte agar plates. Eight E. coil-like colonies re presenting all of the morphological types were transferred to MacConke y agar. A total of 1,080 E. coil isolates were examined, and the ehxA gene was detected in 12 independent strains, only 3 of which were posi tive for slt.We concluded that the ehxA gene was less correlated with virulence than the eae gene was and that EHEC hemolysin alone has limi ted value for screening bovine feces for pathogenic SLTEC because of p resence of the ehxA gene in bovine isolates that are not SLTEC.