title: Genetic characterization of mcr-1-bearing plasmids to depict molecular mechanisms underlying dissemination of the colistin resistance determinant.
abstract: To analyse and compare mcr-1-bearing plasmids from animal Escherichia coli isolates, and to investigate potential mechanisms underlying dissemination of mcr-1.
  
  
  
  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.
  
  
  
  Three major types of mcr-1-bearing plasmids were recovered: IncX4 (∼33 kb), IncI2 (∼60 kb) and IncHI2 (∼216-280 kb), among which the IncX4 and IncI2 plasmids were found to harbour the mcr-1 gene only, whereas multiple resistance elements including blaCTX-M, blaCMY, blaTEM, 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-mcr-1-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-ISApl1 was found to be the key element mediating translocation of mcr-1 into various plasmid backbones through formation of a circular intermediate.
  
  
  
  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.
authors.affiliation: Shenzhen Key Lab for Food Biological Safety Control, Food Safety and Technology Research Center, Hong Kong PolyU Shen Zhen Research Institute, Shenzhen, P. R. China.|The State Key Lab of Chirosciences, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR.
authors.forename: Ruichao
authors.initials: R
authors.lastname: Li
authors.affiliation: Shenzhen Key Lab for Food Biological Safety Control, Food Safety and Technology Research Center, Hong Kong PolyU Shen Zhen Research Institute, Shenzhen, P. R. China.
authors.forename: Miaomiao
authors.initials: M
authors.lastname: Xie
authors.affiliation: Shenzhen Key Lab for Food Biological Safety Control, Food Safety and Technology Research Center, Hong Kong PolyU Shen Zhen Research Institute, Shenzhen, P. R. China.
authors.forename: Jinfei
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Shenzhen Key Lab for Food Biological Safety Control, Food Safety and Technology Research Center, Hong Kong PolyU Shen Zhen Research Institute, Shenzhen, P. R. China.
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Yang
authors.affiliation: Shenzhen Key Lab for Food Biological Safety Control, Food Safety and Technology Research Center, Hong Kong PolyU Shen Zhen Research Institute, Shenzhen, P. R. China.
authors.forename: Lizhang
authors.initials: L
authors.lastname: Liu
authors.affiliation: Shenzhen Key Lab for Food Biological Safety Control, Food Safety and Technology Research Center, Hong Kong PolyU Shen Zhen Research Institute, Shenzhen, P. R. China.
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Liu
authors.affiliation: Shenzhen Key Lab for Food Biological Safety Control, Food Safety and Technology Research Center, Hong Kong PolyU Shen Zhen Research Institute, Shenzhen, P. R. China.
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Zheng
authors.affiliation: The State Key Lab of Chirosciences, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR.
authors.forename: Edward Wai-Chi
authors.initials: EW
authors.lastname: Chan
authors.affiliation: Shenzhen Key Lab for Food Biological Safety Control, Food Safety and Technology Research Center, Hong Kong PolyU Shen Zhen Research Institute, Shenzhen, P. R. China sheng.chen@polyu.edu.hk.|The State Key Lab of Chirosciences, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR.
authors.forename: Sheng
authors.initials: S
authors.lastname: Chen
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002681:China; D003091:Colistin / Q000494:pharmacology*; D019295:Computational Biology; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics*; D000072480:Farms; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D020071:Interspersed Repetitive Sequences; D008826:Microbial Sensitivity Tests; D010957:Plasmids / Q000145:classification*; D017422:Sequence Analysis, DNA; D013552:Swine / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; C000614037:MCR-1 protein, E coli; D003091:Colistin