A 1-Year Investigation of Extended-Spectrum Beta-Lactamase-Producing and Isolated from Bovine Mastitis at a Large-Scale Dairy Farm in Japan

In a large-scale dairy farm, it is important to take countermeasure of prevention against mastitis of dairy cows, and it is especially important to establish hygiene and risk management to prevent the emergence and spread of antibiotic-resistant bacteria. In this study, we have performed bacteriological testing of clinical and subclinical mastitis and investigation of antimicrobial resistance bacteria in a large-scale farm for 1 year. The bacteria isolated most frequently from 1,549 samples of 952 cow, including cows with recurring mastitis were non- (SNA) (27.6%), followed by (18.9%), (12.3%). Although was isolated at 7.7% from milk sample, no methicillin-resistant was found. The incidence of extended-spectrum β-lactamase (ESBL)-producing was 1.4% and ESBL-producing was 1.4% of all samples, even though third- and fourth-generation cephalosporins were not used for antimicrobial treatment of mastitis in this farm. Although these genotypes of ESBL-producing and were mainly composed of CTX-M-15 and TEM-1 and CTX-M-2 and TEM-116, respectively, there was no spread and persist of predominant clonal type. Appropriate farm management, such as segregation and culling of infected animals and monitors of trends in antimicrobial resistance among mastitis pathogens, may have contributed these results.