Abstract
Extended-spectrum β-lactamase (ESBL)–producing Escherichia coli have been frequently isolated from food-producing animals and pose a serious threat to human health. This study collected 195 ESBL-producing E. coli isolates from 20 chicken farms and 3 live-bird markets located in Northeast China (Heilongjiang, Liaoning, Jilin) and Jiangsu province from February 2011 to October 2013. ESBL genes, including bla CTX-M, bla TEM, and bla SHV, were detected and characterized, and the susceptibilities of these strains to various antimicrobial agents were determined. One hundred ninety-one of these isolates carried 1 or more bla genes. bla CTX-M, bla TEM-1, and bla SHV-5 were identified in 183, 121, and 2 isolates, respectively. The most common bla CTX-M genes were bla CTX-M-15 (68 strains), bla CTX-M-65 (41 strains), bla CTX-M-55 (35 strains), bla CTX-M-14 (32 strains), followed by bla CTX-M-3, bla CTX-M-13, bla CTX-M-79, and bla CTX-M-101, as well as the chimeric genes bla CTX-M-64, bla CTX-M-123, and bla CTX-M-132. Fifteen strains (7.7%) co-harboring CTX-M-1 group and CTX-M-9 group genes were detected in 195 ESBL-producing strains. Pulsed-field gel electrophoresis of 45 strains showed that these CTX-M-producing isolates belonged to 34 different types. To our knowledge, this is the first study to report the bla SHV-5 gene in E. coli isolated from chickens in China. Conjugation experiments demonstrated that the bla CTX-M and bla TEM genes could be transferred to E. coli strain J53, while conjugative transfer of the bla SHV-5 gene from two isolates was not detectable. bla CTX-M genes are carried by many kinds of transferable and untypable plasmids. Our findings demonstrate that the CTX-M enzymes are predominant in both type and quantity.
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