DETECTION AND LONG-TERM EXISTENCE OF SHIGA TOXIN (STX)-PRODUCING ESCHERICHIA-COLI IN SHEEP

The isolation and characterization of Shiga-like toxin (Stx)-producing Escherichia coli (STEC) from sheep are described. The distribution of stx genes in E. coli isolates was detected by PCR, When brain heart i nfusion (BHI) broth and novobiocin supplemented m-EC broth (N-mEC) wer e used as enrichment culture for the isolation of STEC, N-mEC, compare d to BHI, showed clearly lower efficiency. Finally, 5 STEC isolates fr om 4 sheep were isolated and characterized by biochemical and genetica l analysis. All of them were confirmed by ELISA and Vero cell cytotoxi city assay for the production of Stx, Moreover, some strains carried h emolysin and eaeA genes and harbored large plasmids, Based on their pl asmid profiles, antibiotic patterns and PCR-based DNA fingerprinting a nalysis using random amplified polymorphic DNA (RAPD), all isolates we re different from each other. Three of the isolates were identified to belong to serogroups O2, O153 and O165, respectively, and the STEC st rains belonging to these serogroups had been isolated from STEC outbre aks in humans. Four months after the first isolation in July 1997, STE C from sheep #1 was isolated again. A new isolate, HI-11, was identifi ed as STEC O2:Hnt, Simultaneously, 2 STEC, which were genetically and phenotypically different from each other, were isolated from the same sheep at intervals of 4 months. These results demonstrate that sheep m ay be an important animal for studying human STEC infections, and that further epidemiological surveys on STEC are necessary.