Antimicrobial susceptibility and characterization of extended-spectrum beta-lactamases in Escherichia coli isolated from bovine mastitic milk in South Korea from 2012 to 2015

作者：Tark Dong Seob; Moon Dong Chan; Kang Hee Young; Kim Su Ran; Nam Hyang Mi; Lee Hee Soo; Jung Suk Chan; Lim Suk Kyung^*

来源：Journal of Dairy Science, 2017, 100(5): 3463-3469.

DOI：10.3168/jds.2016-12276

• extended-spectrum beta-lactamase
• bovine mastitic milk
• Escherichia coli
• multidrug resistance

In this study, we aimed to assess trends in antimicrobial resistance and to investigate the characteristics of extended-spectrum beta-lactamase (ESBL)-producing isolates from bovine mastitic milk from 2012 to 2015. A total of 374 Escherichia coli isolates were analyzed (154 in 2012, 113 in 2013; 76 in 2014, and 31 in 2015). No consistent trends in antimicrobial resistance of E. coli isolates occurred during the 4-yr period. The most frequently observed resistance was tetracycline (23.3%), followed by streptomycin (17.1%), ampicillin (16.6%), neomycin (11.8%), and trimethoprim/sulfamethoxazole (11.2%). Multidrug resistance was observed in 15.5% of isolates. Among these isolates, 15 (4.0%) carried one or more bla(CTX-M) and AmpC ESBL genes from 11 different farms, including bla(CTX-M-15) at 4 farms, bla(CTX-M-3) at 2 farms, bla(CTX-M-1) at 3 farms, and bla(CMY-2) at 3 farms. This study is the first report of bla(CTX-M-3)-producing E. cob in dairy milk. Transfer of ESBL was observed in 3 bla(CTX-M-3)-producing isolates, 1 bla(CTX-M-1)-producing isolate, and all 3 bla(CMY-2)-producing isolates. Almost all bla(CTX-M-15) and bla(CTX-M-1) genes possessed an insertion sequence, ISECP1, upstream of the bla(CTX-M) gene. Identical pulsed-field gel electrophoresis profiles were also observed in bla(CTX-M)-producing E. coli from the same farm. These results suggested that ESBL might spread by both clonal and horizontal spread in dairy farms in South Korea. Although no significant changes occurred in the antimicrobial resistance of E. coli during the 4-yr study period, the resistance rates and presence of ESBL were high compared with those in other countries. Thus, these findings suggest the importance of control measures for E. coli, particularly ESBL-producing bacteria, on dairy farms to reduce treatment failure and transmission to humans.

• 出版日期2017-5