Bacterial Disease Division, Animal, Plant, and Fisheries Quarantine and Inspection Agency, Anyang, Gyeonggi-do, Korea.
Foodborne Pathog Dis. 2013 Jan;10(1):13-20. doi: 10.1089/fpd.2012.1245. Epub 2012 Dec 4.
The purpose of this study was to determine the prevalence and characteristics of CTX-M β-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 β-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 β-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 bla(TEM-1) gene was associated with CTX-M β-lactamase in 55 E. coli isolates. Transfer of bla(CTX-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 bla(CTX-M) genes in 117 and 91 E. coli isolates, respectively. Our results demonstrated that a combination of clonal expansion and horizontal transmission is spreading bla(CTX-M) genes among swine E. coli. The horizontal dissemination of bla(CTX-M) genes among E. coli was mostly mediated by IncF or IncI1-Iγ 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 β-lactamases in bacterial isolates from food animals in Korea. This study revealed that the CTX-M β-lactamase-producing E. coli are widely disseminated among healthy pigs but very rare in cattle in Korea. Increasing prevalence of bla(CTX-M) genes in intestinal E. coli of food animals is a matter of concern and should be carefully monitored.
本研究旨在确定韩国健康猪和牛源大肠杆菌中 CTX-M 型β-内酰胺酶的流行情况和特征。从健康猪（n=558）和牛（n=654）粪便中采集了 1212 份粪便样本，筛选出产 CTX-M 型扩展谱β-内酰胺酶（ESBL）的大肠杆菌分离株。对 121 株产 ESBL 的大肠杆菌进行了表型和基因型特征分析。与牛粪便样本相比（1/654，0.2%），猪粪便样本中 CTX-M 型β-内酰胺酶阳性大肠杆菌的检出率较高（120/558，21.5%）。鉴定出的最主要 CTX-M 型为 CTX-M-14（n=82），其次是 CTX-M-15（n=16）。还鉴定出了产 CTX-M-3、CTX-M-27、CTX-M-55 和 CTX-M-65 的分离株。总体而言，55 株产 CTX-M 型大肠杆菌中 bla(TEM-1)基因与 CTX-M β-内酰胺酶相关。76 株 bla(CTX-M)阳性大肠杆菌中有 76 株可通过接合将 bla(CTX-M)基因转移到受体大肠杆菌 J53 中。从转导子中分离出的质粒 DNA 显示出一个大的（90-120 Kb）可接合质粒。在 117 株和 91 株大肠杆菌中分别检测到 bla(CTX-M)基因上下游的 ISEcp1 和 IS903。我们的结果表明，克隆扩张和水平传播的结合正在使 bla(CTX-M)基因在猪源大肠杆菌中传播。大肠杆菌中 bla(CTX-M)基因的水平传播主要由 IncF 或 IncI1-Iγ 质粒介导。据我们所知，本研究首次报道了韩国食源动物分离株中的 CTX-M-3、CTX-M-27、CTX-M-55 和 CTX-M-65 β-内酰胺酶。本研究表明，韩国健康猪中 CTX-M 型β-内酰胺酶阳性大肠杆菌广泛传播，但在牛中非常罕见。食源性动物肠道中 bla(CTX-M)基因的检出率不断增加令人担忧，应予以密切监测。
