ABSTRACT. The prevalence of enterohemorrhagic Escherichia coli (EHEC) O157 was examined in bovine faeces. EHEC O157 was isolated from the faeces of 42 (13.0%) of 324 cattle. Of the 4 farms and the facilities tested, the 3 farms and the facilities wer e found positive for EHEC O157. The highest isolation rate among the farms was 33.7%. The prevalence of EHEC O157 in heifers was higher than that in calves and other cattle. No cattle positive for EHEC O157 showed any clinical signs except 2 calves with diarrhea in a veterinary hospital. Almost all isolates possessed the stx gene, and Stx-positive strains carrying both stx 1 and stx 2 genes were predominant. These results indicate that EHEC O157 are distributed in bovine faeces, and that dairy and beef farms in selected regions of Japan are heavily contaminated with the organisms. KEY WORDS: cattle, EHEC O157, prevalence.

ABSTRACT. A long-term study was performed on the prevalence of enterohemorrhagic Escherichia coli (EHEC) O157 in bovine faeces. The present study was conducted on heifers raised on a farm showing a high isolation rate of EHEC O157 in previous years. The p revalence of EHEC O157 isolated from faecal samples was 10.6% (222/2104), 5.6% (181/3225), and 5.6% (153/2744) from 1998 to 2000, respectively. The numbers of EHEC O157-positive heifers for the same 3 years were 46.3% (185/400), 36.8% (147/399), and 31.7% (130/410), respectively. The seasonal prevalence of EHEC O157 varied according to the year. Most positive heifers excreted the EHEC O157 only once during the survey, though it was excreted 2 or 3 times by some heifers. The results obtained in the present study showed that the farm examined was heavily contaminated with EHEC O157. It is assumed that EHEC O157 does not remain in individual catt le long-term, but does exist long-term on farms due to repeated infection.