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.

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Some ω‐3‐coumarinyl)alkanoic acids 1a, n = 3‐6 were synthesized by cyclization of corresponding ethyl o‐formylphenyl alkanedioate 3 with DBU followed by hydrolysis. By a similar cyclization, some ω‐(2‐chromonyl)alkanoic acids 2a, n = 3‐6 were also obtained from the cyclization of corresponding o‐acetylphenyl ethyl alkanedioate 4.

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