Colistin Resistance Gene mcr-1 and Its Variant in Escherichia coli Isolates from Chickens in China

Abstract

The mcr-1 gene was detected in 5.11% (58/1136) of Escherichia coli isolates of chicken origin from 13 provinces in China. A novel mcr-1 variant, named mcr-1.3, encoding an Ile-to-Val functional variant of MCR-1 was identified in a sequence type 155 (ST155) strain. An mcr-1.3-containing IncI2 plasmid, pHeN867 (60,757 bp), was identified. The transfer of pHeN867 led to a 32-fold increase in the MIC of colistin in the recipient, exhibiting an effect on colistin resistance that was similar to that of mcr-1. KEYWORDS E. coli, colistin resistance, mcr-1.3, plasmid P olymyxins (polymyxin B and colistin) are a last-resort treatment for infections caused by multidrug-resistant (MDR) Gram-negative bacteria (1). In veterinary use, colistin is administered with food in pig and poultry farming to prevent infections caused by pathogens (2). The mcr-1 gene, which confers plasmid-mediated colistin resistance to Enterobacteriaceae, was identified in an IncI2 plasmid from Escherichia coli and Klebsiella pneumoniae in China in 2016 (3). The mcr-1 gene found in E. coli (4), K. pneumoniae (5), and Salmonella spp. (6) has been proven to disseminate ubiquitously. The transmission of mcr-1-mediated colistin resistance between animals and human has been a threat to human health. It has also been demonstrated that the mcr-1 gene can coexist with bla CTX-M (5), bla NDM (7), and other resistance genes (4), which threatens a return of untreatable infections worldwide. Previous reports described the unique mcr-1 gene sequence compared with that of the originally published sequence (3), which indicates that mcr-1 is relatively conserved. Recently, a point mutation of A¡T at position 8 in mcr-1 was identified in K. pneumoniae (8). To investigate the epidemiology of mcr-1 and its variant, E. coli isolates collected from chickens nationwide in China were assessed.In total, 1,136 nonduplicate E. coli isolates were collected between 2010 and 2015 from sick chickens in 20 provinces and municipalities in China. All of these isolates were preliminarily screened on Mueller-Hinton agar medium with 2 g/ml colistin. Because the cooccurrence of mcr-1 with bla CTX-M may accelerate the transmission of resistance to colistin and cephalosporins, the mcr-1 (3) and bla CTX-M (9) genes were detected by PCR amplification of the isolates with resistance to colistin. The corresponding primers used to amplify the whole mcr-1 gene and parts of the ISApl1 element are listed in Table S1 in the supplemental material. For all of the positive PCR products of mcr-1, Sanger sequencing was performed (Tsingke Biological Technology, Chengdu, China) by using a DNA analyzer (Applied Biosystems, Life Technologies, Carlsbad, CA). We found a total of 58 (5.11%) mcr-1-positive isolates, including one isolate harboring the mcr-1 gene with mutations not found in the originally published gene sequence (3). MICs of colistin

Prevalence and Molecular Characteristics of Avian-Origin mcr-1-Harboring Escherichia coli in Shandong Province, China

“…CTX-M-producing enterobacteria are widespread among human populations, but an increasing number of reports have described their presence in food animals and their environment (Li et al, 2007;Ewers et al, 2012;Lazarus et al, 2015). In the present study, 88.2% of the mcr-1 positive isolates carried bla CTX−M , which was similar to a previous study in which more than half of the chicken-origin mcr-1 positive strains presented the coexistence of the mcr-1 and bla CTX−M genes (Yang et al, 2017), but higher than the 43.1% mcr-1 positive isolates carrying bla CTX−M genes. The increasing prevalence and dissemination of co-carriage of ESBL genes in mcr-1 positive E. coli isolates found in our study suggested that it may add challenge to the global problem of difficult to treat and untreatable infections.…”

Population structure and antimicrobial resistance traits of avian‐origin mcr‐1 ‐positive Escherichia coli in Eastern China, 2015 to 2017

“…The mcr‐1 was present in 172 (12.6%) of E. coli isolates in China, from 2015 to 2017. The prevalence of mcr‐1 in avian‐origin E. coli was higher than that reported by Yang et al, (). Over time, the mcr‐1 gene was the more frequently observed in avian‐origin E. coli .…”

“…The mcr‐1 gene was detected in 5.11% (58/1136) of chicken‐origin E. coli isolates from 13 provinces in China, from 2010 to 2015 (Yang et al, ). Half of the chicken‐origin MCRPEC strains presented the coexistence of mcr‐1 and bla CTX‐M genes (Yang et al, ). In this study, our result confirmed the aforementioned findings.…”

“…Over time, the mcr‐1 gene was the more frequently observed in avian‐origin E. coli . Yang et al, () showed that 40 STs were identified in 58 MCRPEC strains, and four STs (ST48, ST10, ST616, and ST88) were the most common. Our result revealed that avian‐origin MCRPEC were widely distributed throughout 52 unique STs.…”

“…The mcr ‐harbouring E. coli isolates were preliminary screened by PCR amplification using the special primer pairs for mcr‐1 , mcr‐2 , mcr‐3 , mcr‐4 , and mcr‐5 genes (Rebelo et al, ). To identify variants of mcr‐1 , full‐length nucleotide sequence of mcr‐1 gene among MCRPEC strains was determined by direct sequencing from PCR products, and BLAST analysis (http://www.ncbi.nlm.nih.gov/) (Yang et al, ). Colistin resistance of MCRPEC clinical isolates was determined by testing the minimum inhibitory concentrations (MICs) via the CAMHB broth dilution method according to the Performance Standards for Antimicrobial Susceptibility Testing released from the Clinical and Laboratory Standards Institute (CLSI) (CLSI, ).…”