Characteristics of Transmissible CTX-M- and CMY-Type β-Lactamase-Producing Escherichia coli Isolates Collected from Pig and Chicken Farms in South Korea

The rapid dissemination of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli has significantly contributed to public health hazard globally. A total of 281 E. coli strains recovered from pigs and chickens between 2009 and 2015 in South Korea were analyzed for ESBL production. ESBL phenotypes were recognized in 14 E. coli isolates; ten and three ESBLproducing isolates carried only bla(CTX-M) and bla(CMY) genes, respectively, and one isolate harbored both genes. The predominant CTX-M and CMY types were CTX-M-15 (n = 8) and CMY-2 (n = 3). We also detected ESBL-producing isolates harboring bla(CTX-M-65), bla(CTX-M-14), bla(CMY-6), bla(DHA-1), and bla(TEM-1) genes. All ESBL-producing isolates showed resistance to the extent of the fourth generation cephalosporins, along with multidrug resistance. CTX-M-15-producing isolates showed higher MIC values than CTX-M-14-and CTX-M-65-producing isolates. The bla(CTX-M) and bla(CMY) genes have the potential to be transferable. The spreading of bla(CMY) and bla(CTX-M) genes w as arbitrated mainly v ia F rep a nd I ncI1 plasmids. Our i solates showed clonal diversity in PFGE analysis. This is the first report of E. coli isolates carrying bla(CMY-6) in chicken from South Korea. The emergence of CMY-6 ESBLs in a population of poultry suggests that extensive screening with long-term surveillance is necessary to prevent the dissemination of ESBL from chicken to human.