Molecular characterization of extended-spectrum β-lactamase-producing Escherichia coli isolates from chickens in Henan Province, China

Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli has spread rapidly worldwide and poses a serious threat to human and animal health. This study collected 51 non-replicate E coli isolates from 14 different chicken farms in Henan Province in China from December 2007 to August 2008. The prevalence of ESBL-producing E coli, molecular characterization of the ESBL-related b/a genes, including b/a(TEM), b/a(SHV) and b/a(CTX-M), and the susceptibilities of these bacteria to various antimicrobial agents were determined. Thirty-one of the 51 isolates were positive for an ESBL phenotype and 29 of these isolates carried one or more b/a genes. Twenty-two isolates harboured b/aTEM genes and 15 isolates carried b/a(CTX-M) genes (one CTX-M-14, three CTX-M-24 and 11 CTX-M-65). One isolate carried b/a(TEM-57); the remaining b/a(TEM) isolates carried b/a(TEM-1) with one silent nucleotide base variation (T18C). We believe that this is the first study to report TEM-57 in E coli isolates. All isolates harbouring b/a(CTX-M-24) and b/a(CTX-M-14) and five of the b/a(CTX-M-65) isolates also harboured the b/a(TEM-1) gene. To our knowledge, this study is the first to describe detection of CTX-M-65-producing E coli isolated from chickens. None of the isolates contained the b/a(SHV) gene. Conjugation experiments demonstrated that b/a(CTX-M) and b/a(TEM) genes could be transferred to E. coli DH5 alpha. The results indicate that ESBL frequency has reached an alarming level in chicken isolates in China, with TEM-1 and CTX-M-65 enzymes being the two predominant beta-lactamases detected.