Department of Medical Microbiology and Parasitology, Zhejiang University School of Medicine, Hangzhou, 310058, Zhejiang, China.
National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, College of Veterinary Medicine, South China Agricultural University, Guangzhou, 510642, Guangdong, China.
Microbiome. 2017 Jul 6;5(1):70. doi: 10.1186/s40168-017-0288-0.
Polymyxin is a cationic polypeptide antibiotic that can disrupt bacterial cell membrane by interacting with its lipopolysaccharide molecules and is used as a last resort drug against lethal infections by the carbapenem-resistant superbugs (like NDM-1). However, global discovery of the MCR-1 colistin resistance dramatically challenges the newly renewed interest in colistin for clinical use.
The mcr-1-harboring plasmids were acquired from swine and human Escherichia coli isolated in China, from 2015 to 2016, and subjected to Illumina PacBio RSII and Hi-Seq2000 for full genome sequencing. PCR was applied to close the gap of the assembled contigs. Ori-Finder was employed to predict the replication origin (oriC) in plasmids. The phenotype of MCR-1-producing isolates was evaluated on the LBA plates with various level of colistin. Genetic deletion was used to test the requirement of the initial "ATG" codon for the MCR-1 function.
Here, we report full genomes of over 10 mcr-1-harboring plasmids with diversified replication incompatibilities. A novel hybrid IncI2/IncFIB plasmid pGD17-2 was discovered and characterized from a swine isolate with colistin resistance. Intriguingly, co-occurrence of two unique mcr-1-bearing plasmids (pGD65-3, IncI2, and pGD65-5, IncX4) was detected in a single isolate GD65, which might accelerate dissemination of the mcr-1 under environmental selection pressure. Genetic analyses of these plasmids mapped mobile elements in the context of antibiotic resistance and determined two insertion sequences (ISEcp1 and ISApl1) that are responsible for the mobilization of mcr-1. Gene deletion also proved that the first ATG codon is redundant in the mcr-1 gene.
Collectively, our results extend landscapes of the diversified mcr-1-bearing plasmid reservoirs.
多黏菌素是一种阳离子多肽抗生素，通过与脂多糖分子相互作用破坏细菌细胞膜，被用作治疗碳青霉烯类耐药超级细菌（如 NDM-1）引起的致命感染的最后手段药物。然而，全球发现的 MCR-1 多黏菌素耐药性对重新引发人们对多黏菌素临床应用的兴趣构成了巨大挑战。
从 2015 年至 2016 年，从中国分离的猪和人源大肠杆菌中获得携带 mcr-1 的质粒，并进行 Illumina PacBio RSII 和 Hi-Seq2000 全基因组测序。PCR 用于闭合组装的 contigs 之间的缺口。Ori-Finder 用于预测质粒中的复制起点（oriC）。通过在 LBA 平板上用不同水平的多黏菌素评估 MCR-1 产生菌的表型。通过基因缺失来测试 MCR-1 功能对初始“ATG”密码子的要求。
在此，我们报告了超过 10 个携带 mcr-1 的质粒的全基因组序列，这些质粒具有多样化的复制不兼容性。从一株具有多黏菌素耐药性的猪源分离株中发现并鉴定了一种新型的混合 IncI2/IncFIB 质粒 pGD17-2。有趣的是，在单个分离株 GD65 中检测到两个独特的 mcr-1 携带质粒（pGD65-3，IncI2 和 pGD65-5，IncX4）的共存，这可能会加速 mcr-1 在环境选择压力下的传播。对这些质粒的遗传分析将移动元件置于抗生素耐药性的背景下，并确定了两个负责 mcr-1 转移的插入序列（ISEcp1 和 ISApl1）。基因缺失也证明了 mcr-1 基因中的第一个 ATG 密码子是多余的。
总之，我们的研究结果扩展了携带 mcr-1 的质粒多样化的景观。
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