Study of mcr-1 Gene-Mediated Colistin Resistance in Enterobacteriaceae Isolated from Humans and Animals in Different Countries
Unité de Recherche sur les Maladies Infectieuses et Tropicales Émergentes (URMITE), UMR CNRS, IHU Méditerranée Infection, Faculté de Médecine et de Pharmacie, Aix-Marseille-University, Marseille 13005, France
Monash Biomedicine Discovery Institute, Department of Microbiology, Monash University, Parkville, Victoria 3800, Australia
Author to whom correspondence should be addressed.
Academic Editor: Bruno González-Zorn
Genes 2017, 8(12), 394; https://doi.org/10.3390/genes8120394
Received: 4 October 2017 / Revised: 22 November 2017 / Accepted: 12 December 2017 / Published: 19 December 2017
(This article belongs to the Section Microbial Genetics and Genomics)
In this study, we aim to characterize the genetic environment of the plasmid-mediated colistin resistance gene mcr-1 in 25 Escherichia coli and seven Klebsiella pneumoniae strains from different countries and continents. Multilocus sequence typing, conjugation experiments, plasmid typing, and the presence and location of the insertion sequence ISApl1 were investigated. Whole genome sequencing of four E. coli was performed to analyse the genetic environment of the mcr-1 gene. Colistin minimum inhibitory concentration of mcr-1 strains varied from 3 to 32 µg/mL. Six E. coli sequence types were detected: ST 4015, ST 3997, ST 10, ST 93, ST 48, and ST 648. IncHI2, IncI2, and IncP plasmid types were predominant and were unrelated to a specific country of origin. ISApl1 was found in 69% of analysed plasmids that were mainly around the mcr-1 gene. Analysis of four closed mcr-1 plasmids revealed the integration of mcr-1 into hotspots. We found that the spread of mcr-1 gene was due to the diffusion of a composite transposon and not to the diffusion of a specific plasmid or a specific bacterial clone. The ease with which the mcr-1 gene integrates into various regions facilitates its dissemination among bacteria and explains its large diffusion all over the world, both in animals and in humans.