Genetic analysis of shiga‐toxigenic Escherichia coli isolates from cattle in a limited region

ABSTRACT The ecology of shiga‐toxigenic Escherichia coli (STEC) is important in the animal production environment. We investigated fecal shedding of STEC in one town in Miyagi, Japan by multiplex polymerase chain reaction (PCR) targeting shiga toxin gene 1 (stx1), gene 2 (stx2) and malB promoter gene, and analyzed the PCR products of stx1 or stx2 (54 samples) by direct sequencing. Three of 46 (6.5%) beef cattle in the University Farm of Tohoku University (Kawatabi Farm) and 11 of 70 (15.7%) calves in neighboring dairy farms carried STEC. Rate of detecting genes of stx1, stx2 and stx1+2 was 3.4% (4/116), 8.6% (10/116) and 0.9% (1/116), respectively. Serotyping indicated that STEC contaminated farms at different times or through different routes. Isolates harbored no mutation among stx1, but six (Kawatabi Farm) and 38 (neighboring farms) base substitutions among stx2, respectively. The diversity of substitutions of stx2 was observed among farms or even in a farm. Phylogenic analysis revealed that STEC detected in the area were classified into three clusters by the variety of stx2. Sequence analysis of stx2 will be one of the tools for clarifying the source of outbreaks and the route of contamination of STEC.