Emergence of plasmid mediated colistin resistance mechanism MCR 1 in animals and human beings in China: a microbiological and molecular biological study.
BACKGROUND Until now, polymyxin resistance has involved chromosomal mutations but has never been reported via horizontal gene transfer. During a routine surveillance project on antimicrobial resistance in commensal Escherichia coli from food animals in China, a major increase of colistin resistance was observed. When an E coli strain, SHP45, possessing colistin resistance that could be transferred to another strain, was isolated from a pig, we conducted further analysis of possible plasmid mediated polymyxin resistance. Herein, we report the emergence of the first plasmid mediated polymyxin resistance mechanism, MCR 1, in Enterobacteriaceae. METHODS The mcr 1 gene in E coli strain SHP45 was identified by whole plasmid sequencing and subcloning. MCR 1 mechanistic studies were done with sequence comparisons, homology modelling, and electrospray ionisation mass spectrometry. The prevalence of mcr 1 was investigated in E coli and Klebsiella pneumoniae strains collected from five provinces between April, 2011, and November, 2014. The ability of MCR 1 to confer polymyxin resistance in vivo was examined in a murine thigh model. FINDINGS Polymyxin resistance was shown to be singularly due to the plasmid mediated mcr 1 gene. The plasmid carrying mcr 1 was mobilised to an E coli recipient at a frequency of 10( 1) to 10( 3) cells per recipient cell by conjugation, and maintained in K pneumoniae and Pseudomonas aeruginosa. In an in vivo model, production of MCR 1 negated the efficacy of colistin. MCR 1 is a member of the phosphoethanolamine transferase enzyme family, with expression in E coli resulting in the addition of phosphoethanolamine to lipid A. We observed mcr 1 carriage in E coli isolates collected from 78 (15% of 523 samples of raw meat and 166 (21% of 804 animals during 2011 14, and 16 (1% of 1322 samples from inpatients with infection. INTERPRETATION The emergence of MCR 1 heralds the breach of the last group of antibiotics, polymyxins, by plasmid mediated resistance. Although currently confined to China, MCR 1 is likely to emulate other global resistance mechanisms such as NDM 1. Our findings emphasise the urgent need for coordinated global action in the fight against pan drug resistant Gram negative bacteria. FUNDING Ministry of Science and Technology of China, National Natural Science Foundation of China.
The Lancet. Infectious diseases