Genetic characterization of mcr-1-bearing plasmids to depict molecular mechanisms underlying dissemination of the colistin resistance determinant
Genetic characterization of mcr-1-bearing plasmids to depict molecular mechanisms underlying dissemination of the colistin resistance determinant
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DOI：
10.1093/jac/dkw411
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发表时间：
2017-02-01
影响因子：
5.2
通讯作者：
Chen, Sheng
中科院分区：
文献类型：
--
作者：
Li, Ruichao;Xie, Miaomiao;Chen, Sheng
目的：分析和比较动物大肠杆菌分离株携带mcr-1的质粒，探讨mcr-1传播的潜在机制。方法：对97株产esbl大肠杆菌进行mcr-1基因筛选。对15株mcr-1阳性菌株所携带的携带mcr-1的质粒进行了分子表征和生物信息学分析。结果：共获得3种主要携带mcr-1的质粒：IncX4（类似于33 kb）、IncI2（类似于60 kb）和IncHI2（类似于216-280 kb），其中IncX4和IncI2质粒仅携带mcr-1基因，而在IncHI2质粒中，除了mcr-1外，还检测到bla（CTX-M）、bla（CMY）、bla（TEM）、fosA、qnrS、floR和oqxAB等多种耐药元件。试验菌株携带mcr-1质粒的谱变化很大，常见的是同时携带两个mcr-1质粒。然而，黏菌素的MIC不受携带mcr-1质粒数量的影响。质粒的比较分析表明，它们含有不同结构的mcr-1基因盒（mcr-1-orf、ISApl1-mcr1- orf和Tn6330），其中IncHI2型获取外源抗性基因最为活跃。一种结构为isapl1 -mcr-1-orf- isapl1的新型转座子Tn6330被发现是介导mcr-1通过形成一个圆形中间体转运到各种质粒主干的关键元件。结论：mcr-1基因可通过Tn6330、Tn6330的环状中间体和含有这些元件的质粒等多种移动元件传播。它通常通过IncHI2质粒与其他抗性决定因素共同传播。Tn6330是一种典型的携带mcr-1的复合转座子，其功能机制有待进一步研究。
Objectives: To analyse and compare mcr-1-bearing plasmids from animal Escherichia coli isolates, and to investigate potential mechanisms underlying dissemination of mcr-1.Methods: Ninety-seven ESBL-producing E. coli strains isolated from pig farms in China were screened for the mcr-1 gene. Fifteen mcr-1-positive strains were subjected to molecular characterization and bioinformatic analysis of the mcr-1-bearing plasmids that they harboured.Results: Three major types of mcr-1-bearing plasmids were recovered: IncX4 (similar to 33 kb), IncI2 (similar to 60 kb) and IncHI2 (similar to 216-280 kb), among which the IncX4 and IncI2 plasmids were found to harbour the mcr-1 gene only, whereas multiple resistance elements including bla(CTX-M), bla(CMY), bla(TEM), fosA, qnrS, floR and oqxAB were detected, in various combinations, alongside mcr-1 in the IncHI2 plasmids. The profiles of mcr-1-bearing plasmids in the test strains were highly variable, with coexistence of two mcr-1-bearing plasmids being common. However, the MIC of colistin was not affected by the number of mcr-1-carrying plasmids harboured. Comparative analysis of the plasmids showed that they contained an mcr-1 gene cassette with varied structures (mcr-1-orf, ISApl1-mcr1- orf and Tn6330), with the IncHI2 type being the most active in acquiring foreign resistance genes. A novel transposon, Tn6330, with the structure ISApl1-mcr-1-orf-ISApl1was found to be the key element mediating translocation of mcr-1 into various plasmid backbones through formation of a circular intermediate.Conclusions: The mcr-1 gene can be disseminated via multiple mobile elements including Tn6330, its circular intermediate and plasmids harbouring such elements. It is often co-transmitted with other resistance determinants through IncHI2 plasmids. The functional mechanism of Tn6330, a typical composite transposon harbouring mcr-1, should be further investigated.