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Front. Microbiol. | doi: 10.3389/fmicb.2018.00331

Fitness advantage of mcr-1–bearing IncI2 and IncX4 plasmids in vitro

 Renjie Wu1,  Lingxian Yi1, Linfeng Yu1, Jing Wang1,  Yiyun Liu1, Xiaojie Chen1,  Luchao Lv1, Jun Yang1 and  Jian-Hua Liu1*
  • 1College of Veterinary Medicine, South China Agricultural University, China

The objective of this study was to assess the impact of diverse plasmids bearing colistin resistance gene mcr-1 on host fitness. Forty-seven commensal E. coli isolates recovered from the pig farm where mcr-1 was first identified were screened for mcr-1. mcr-1-bearing plasmids were characterized by sequencing. The fitness impact of mcr-1-bearing plasmids was evaluated by in vitro competition assays. Twenty-seven (57.5%) E. coli isolates were positive for mcr-1. The mcr-1 genes were mainly located in plasmids belonging to IncI2 (n=5), IncX4 (n=11), IncHI2/ST3 (n=8), IncFII (n=2), and IncY (n=2). InHI2 plasmids also carried other resistance genes (floR, blaCTX-M, and fosA3) and were only detected in isolates from nursery pigs. Sequences of the representative mcr-1–bearing plasmids were almost identical to those of the corresponding plasmid types reported previously. An increase in the fitness of IncI2- and IncX4-carrying strains was observed, while the presence of IncHI2, IncFII and IncY plasmids showed a fitness cost although an insignificant fitness increase was initially observed in IncFII or IncY plasmids-containing strains. Acquisition of IncI2-type plasmid was more beneficial for host E. coli DH5α than either IncHI2 or IncX4 plasmid, while transformants with IncHI2-type plasmid presented a competitive disadvantage against IncI2 or IncX4 plasmid containing strains. In conclusion, IncI2, IncX4, and IncHI2 were the major plasmid types driving the dissemination of mcr-1 in this farm. Increased fitness or co-selection by other antimicrobials might contribute to the further dissemination of the three epidemic mcr-1–positive plasmids (IncI2, IncX4 and IncHI2) in this farm and worldwide.

Keywords: Escherichia coli, MCR-1, Colistin, Plasmid, fitness

Received: 04 Jan 2018; Accepted: 12 Feb 2018.

Edited by:

Miklos Fuzi, Semmelweis University, Hungary

Reviewed by:

Isabelle Kempf, Agence Nationale de Sécurité Sanitaire de l’Alimentation, de l’Environnement et du Travail (ANSES), France
Alberto Quesada, Universidad de Extremadura, Spain  

Copyright: © 2018 Wu, Yi, Yu, Wang, Liu, Chen, Lv, Yang and Liu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Jian-Hua Liu, South China Agricultural University, College of Veterinary Medicine, Guangzhou, China,