Department of Veterinary and Biomedical Sciences, University of Minnesota, 1971 Commonwealth Avenue, 205 Veterinary Science, St. Paul, MN 55108, USA.
Plasmid. 2011 Sep;66(3):144-51. doi: 10.1016/j.plasmid.2011.07.003. Epub 2011 Aug 6.
Increasing reports of multidrug resistance conferred by conjugative plasmids of Enterobacteriaceae necessitate a better understanding of their evolution. One such group is the narrow-host-range IncI1 plasmid type, known for their ability to carry genes encoding resistance to extended-spectrum beta lactamases. The focus of this study was to perform comparative sequencing of IncI1 plasmids from porcine enterotoxigenic Escherichia coli (ETEC), isolated irrespective of antimicrobial susceptibility phenotype. Five IncI1 plasmids of porcine ETEC origin and one IncI1 plasmid from a Salmonella enterica serovar Kentucky isolate from a healthy broiler chicken were sequenced and compared to existing IncI1 plasmid sequences in an effort to better understand the overall genetic composition of the IncI1 plasmid lineages. Overall, the sequenced porcine ETEC IncI1 plasmids were divergent from other sequenced IncI1 plasmids based upon multiple means of inferred phylogeny. High occurrences of IncI1 and IncA/C plasmid-associated genes and the blaTEM and blaCMY-2 beta lactamase genes were observed among porcine ETEC. However, the presence of blaTEM and blaCMY-2 did not strongly correlate with IncI1 plasmid possession, suggesting that these plasmids in porcine ETEC are not primarily associated with the carriage of such resistance genes. Overall, this work suggests a conservation of the IncI1 plasmid backbone among sequenced plasmids with a single locus for the acquisition of accessory genes, such as those associated with antimicrobial resistance. Furthermore, the high occurrence of IncI1 and IncA/C plasmids among clinical E. coli from commercial swine facilities is indicative of extensive horizontal gene transfer among porcine ETEC.
越来越多的报告表明，肠杆菌科的可接合质粒具有多药耐药性，这需要我们更好地了解它们的进化。其中一个这样的群体是窄宿主范围的 IncI1 质粒类型，其特点是能够携带编码对扩展谱β内酰胺酶的耐药性的基因。本研究的重点是对来自猪肠产毒性大肠杆菌（ETEC）的 IncI1 质粒进行比较测序，这些 ETEC 分离株无论其对抗菌药物的敏感性表型如何。对 5 个源自猪 ETEC 的 IncI1 质粒和 1 个源自健康肉鸡的肠炎沙门氏菌血清型肯塔基分离株的 IncI1 质粒进行了测序，并与现有的 IncI1 质粒序列进行了比较，以便更好地了解 IncI1 质粒谱系的总体遗传组成。总的来说，根据推断的系统发育的多种方法，测序的猪 ETEC IncI1 质粒与其他测序的 IncI1 质粒存在差异。在猪 ETEC 中，IncI1 和 IncA/C 质粒相关基因以及 blaTEM 和 blaCMY-2 内酰胺酶基因的高发生率很常见。然而，blaTEM 和 blaCMY-2 的存在与 IncI1 质粒的存在并没有很强的相关性，这表明这些质粒在猪 ETEC 中主要与携带这些耐药基因无关。总的来说，这项工作表明，在测序的质粒中，IncI1 质粒的骨架是保守的，而单个基因座用于获得辅助基因，如与抗菌药物耐药性相关的基因。此外，商业猪场临床大肠杆菌中 IncI1 和 IncA/C 质粒的高发生率表明猪 ETEC 之间存在广泛的水平基因转移。
