Herd prevalence of Enterobacteriaceae producing CTX-M-type and CMY-2 β-lactamases among Japanese dairy farms.

Aims To determine the herd prevalence of Enterobacteriaceae producing CTX-M-type extended-spectrum β-lactamases (ESBLs) among 381 dairy farms in Japan. Methods and Results Between 2007 and 2009, we screened 897 faecal samples using BTB lactose agar plates containing cefotaxime (2 μg ml−1). Positive isolates were tested using ESBL confirmatory tests, PCR and sequencing for CTX-M, AmpC, TEM and SHV. The incidence of Enterobacteriaceae producing CTX-M-15 (n = 7), CTX-M-2 (n = 12), CTX-M-14 (n = 3), CMY-2 (n = 2) or CTX-M-15/2/14 and CMY-2 (n = 4) in bovine faeces was 28/897 (3·1%) faecal samples. These genes had spread to Escherichia coli (n = 23) and three genera of Enterobacteriaceae (n = 5). Herd prevalence was found to be 20/381 (5·2%) dairy farms. The 23 E. coli isolates showed clonal diversity, as assessed by multilocus sequence typing and pulsed-field gel electrophoresis. The pandemic E. coli strain ST131 producing CTX-M-15 or CTX-M-27 was not detected. Conclusions Three clusters of CTX-M (CTX-M-15, CTX-M-2, CTX-M-14) had spread among Japanese dairy farms. Significance and Impact of the Study This is the first report on the prevalence of multidrug-resistant CTX-M-15–producing E. coli among Japanese dairy farms.