College of Veterinary Medicine, National Reference Laboratory of Veterinary Drug Residues (SCAU), South China Agricultural University, Guangzhou, People's Republic of China.
J Antimicrob Chemother. 2011 Nov;66(11):2475-9. doi: 10.1093/jac/dkr328. Epub 2011 Aug 17.
To investigate the prevalence and characterization of 16S rRNA methylase-producing bacteria in a pig farm and its environment in East China.
Enterobacteriaceae isolates and metagenomic DNA from 102 pig faecal samples from a pig farm and 97 soil samples taken in or around the farm were screened for the presence of 16S rRNA methylase genes. The clonal relationships of 16S rRNA methylase-positive isolates, plasmid content and other associated resistance genes were also characterized.
Fifty-six rmtB-positive Enterobacteriaceae isolates, including 54 Escherichia coli, 1 Morganella morganii and 1 Proteus mirabilis, were recovered from 55 pig faecal samples. Nineteen rmtB-positive bacteria, including 13 E. coli, 2 M. morganii, 2 Leclercia adecarboxylata, 1 Enterobacter aerogenes and 1 Enterobacter cloacae, were recovered from 16 soil samples. Among the 75 rmtB-positive isolates, 31 and 25 also carried the qepA and bla(CTX-M) genes, respectively. The qepA gene co-localized with rmtB on the F2:A-:B1 plasmids and the bla(CTX-M-65) gene co-localized with rmtB on the F33:A-:B- plasmids. The rmtB gene was also found to be associated with the IncN plasmids. Clonal transmission of rmtB-positive E. coli isolates was observed between different pig groups and soil samples.
Both horizontal gene transfer and clonal spread could be responsible for the dissemination of the rmtB gene in the pig farm and its environment. To our knowledge, this study is the first report of rmtB-positive bacteria from farmland soils and indicates that these antibiotic-resistant bacteria and/or resistance genes could be acquired by humans through the food chain.
调查华东地区某猪场及其环境中携带 16S rRNA 甲基化酶的细菌的流行情况和特征。
从华东地区某猪场的 102 份猪粪便样本和 97 份猪场内外土壤样本中筛选出携带 16S rRNA 甲基化酶基因的肠杆菌科分离株和宏基因组 DNA。还对 16S rRNA 甲基化酶阳性分离株的克隆关系、质粒含量和其他相关耐药基因进行了特征分析。
从 55 份猪粪便样本中分离出 56 株 rmtB 阳性肠杆菌科分离株，包括 54 株大肠埃希菌、1 株摩根摩根菌和 1 株奇异变形杆菌。从 16 份土壤样本中分离出 19 株 rmtB 阳性菌，包括 13 株大肠埃希菌、2 株摩根摩根菌、2 株雷氏普罗威登斯菌、1 株产气肠杆菌和 1 株阴沟肠杆菌。在 75 株 rmtB 阳性分离株中，有 31 株和 25 株分别携带 qepA 和 bla(CTX-M)基因。qepA 基因与 rmtB 共定位在 F2:A-:B1 质粒上，bla(CTX-M-65)基因与 rmtB 共定位在 F33:A-:B-质粒上。还发现 rmtB 基因与 IncN 质粒有关。不同猪群和土壤样本之间观察到 rmtB 阳性大肠埃希菌分离株的克隆传播。
水平基因转移和克隆传播都可能是 rmtB 基因在猪场及其环境中传播的原因。据我们所知，这是首次报道农田土壤中存在 rmtB 阳性细菌的研究，表明这些抗生素耐药菌和/或耐药基因可能通过食物链被人类获得。
