National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, People's Republic of China.
Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural University, Guangzhou, People's Republic of China.
Sci Rep. 2017 Mar 24;7(1):424. doi: 10.1038/s41598-017-00095-x.
IncX4 plasmids are associated with the dissemination of the mcr-1 genes in Enterobacteriaceae. We screened IncX4 plasmids among 2,470 isolates of Enterobacteriaceae and determined the mcr-1 positive isolates. Forty-three isolates were observed to carry IncX4 type plasmid, among which 13 were identified to carry mcr-1 gene. Three representative mcr-1-positive IncX4 plasmids were selected for high-throughput sequencing. Comparative genomics showed that the mcr-1-carrying IncX4 plasmids exhibit remarkable similarity in the backbone, and the major distinction lies in the region containing mcr-1. The major variable regions of all the IncX4 plasmids were fully characterized by PCR-RFLP. The results revealed that the mcr-1 was located on the Variable Region I of IncX4 plasmids in 11 E. coli isolates. Among them, nine E. coli strains possess an epidemic pCSZ4-like IncX4 plasmid containing mcr-1. ISApl1 was presumably involved in the transposition of the mcr-1 cassette and then was lost. Similar genetic contexts were found in different plasmids, even the E. coli chromosome, implying the acquisition of mcr-1 by a unique common mechanism.
IncX4 质粒与肠杆菌科中 mcr-1 基因的传播有关。我们在 2470 株肠杆菌科分离株中筛选 IncX4 质粒，并确定 mcr-1 阳性分离株。观察到 43 株分离株携带 IncX4 型质粒，其中 13 株携带 mcr-1 基因。选择了三个具有代表性的 mcr-1 阳性 IncX4 质粒进行高通量测序。比较基因组学显示，携带 mcr-1 的 IncX4 质粒在骨架上具有显著的相似性，主要区别在于包含 mcr-1 的区域。所有 IncX4 质粒的主要可变区均通过 PCR-RFLP 进行了全面表征。结果表明，11 株大肠杆菌分离株中的 mcr-1 位于 IncX4 质粒的可变区 I 上。其中，9 株大肠杆菌菌株含有流行的 pCSZ4 样 IncX4 质粒，其中包含 mcr-1。ISApl1 可能参与 mcr-1 盒的转座，然后丢失。在不同的质粒中甚至在大肠杆菌染色体中都发现了相似的遗传背景，这表明 mcr-1 是通过独特的共同机制获得的。
