Prevalence and molecular characterization of CTX-M ??-lactamase- producing Escherichia coli isolated from healthy swine and cattle

摘要

The purpose of this study was to determine the prevalence and characteristics of CTX-M ??-lactamases in Escherichia coli among healthy swine and cattle in Korea. A total of 1212 fecal samples obtained from healthy pigs (n=558) and cattle (n=654) were screened for CTX-M-type extended spectrum ??-lactamase (ESBL)-producing E. coli isolates. One hundred and twenty-one E. coli that produced ESBL were subjected to phenotypic and genotypic characterization. A high number (120/558, 21.5%) of swine fecal samples showed the presence of CTX-M ??-lactamase-producing E. coli compared to cattle samples (1/654, 0.2%). The most predominant CTX-M-type identified was CTX-M-14 (n=82), followed by CTX-M-15 (n=16). Isolates producing CTX-M-3, CTX-M-27, CTX-M-55, and CTX-M-65 were also identified. Overall, the blaTEM-1 gene was associated with CTX-M ??-lactamase in 55 E. coli isolates. Transfer of blaCTX-M gene was demonstrated from 76 out of 121 bla CTX-M-positive E. coli isolates to the recipient E. coli J53 by conjugation. Plasmid DNA isolation from the transconjugants revealed a large (90-120 Kb) conjugative plasmid. ISEcp1 and IS903 were detected upstream and downstream of blaCTX-M genes in 117 and 91 E. coli isolates, respectively. Our results demonstrated that a combination of clonal expansion and horizontal transmission is spreading blaCTX-M genes among swine E. coli. The horizontal dissemination of blaCTX-M genes among E. coli was mostly mediated by IncF or IncI1-I?? plasmids. To the best of our knowledge, this study represents the first report of CTX-M-3, CTX-M-27, CTX-M-55, and CTX-M-65 ??-lactamases in bacterial isolates from food animals in Korea. This study revealed that the CTX-M ??-lactamase-producing E. coli are widely disseminated among healthy pigs but very rare in cattle in Korea. Increasing prevalence of blaCTX-M genes in intestinal E. coli of food animals is a matter of concern and should be carefully monitored. ? Mary Ann Liebert, Inc.