Dissemination of the mcr-1 colistin resistance gene

Abstract

Yi-Yun Liu and colleagues' study1Liu Y-Y Wang Y Walsh TR et al.Emergence of plasmid-mediated colistin resistance mechanism MCR-1 in animals and human beings in China: a microbiological and molecular biological study.Lancet Infect Dis. 2016; 16: 161-168Summary Full Text Full Text PDF PubMed Scopus (3272) Google Scholar reports the first transferrable colistin resistance gene, mcr-1. A particular concern of this finding is that organisms harbouring this gene are prevalent in pork and chicken, the most popular meat products in China. We postulated that this gene might have already infiltrated into the human microbiome due to frequent contact between the gut flora and food-borne organisms.2Hu Y Liu F Lin YC et al.Dissemination of the mcr-1 colistin resistance gene.Lancet Infect Dis. 2016; 16: 146-147Summary Full Text Full Text PDF PubMed Scopus (111) Google Scholar To test this possibility, we surveyed the presence of mcr-1 in Enterobacteriaceae species isolated from faecal samples of children younger than 5 years. The rationale behind the selection of children as the study sample is that the level of exposure to animal products is relatively low in children; hence, carriage of such genes in the gut flora is expected to be endemic rather than transitory in nature. On Dec 1, 2015, 300 faecal samples were randomly collected from children in hospital to isolate Enterobacteriaceae, with a maximum of two colonies of different morphologies being selected from each sample. 324 strains of different Enterobacteriaceae species, including Escherichia coli (n=234), Klebsiella pneumoniae (n=63), Enterobacter cloacae (n=14), Citrobacter freundii (n=8), and Morganella morganii (n=5) were isolated from these samples and screened for mcr-1 as previously described.1Liu Y-Y Wang Y Walsh TR et al.Emergence of plasmid-mediated colistin resistance mechanism MCR-1 in animals and human beings in China: a microbiological and molecular biological study.Lancet Infect Dis. 2016; 16: 161-168Summary Full Text Full Text PDF PubMed Scopus (3272) Google Scholar Five (2·1%) E coli isolates, but no strains of other species, harboured mcr-1. The table shows the medical history of the five children from whom mcr-1 was recoverable. These children, whose ages ranged between 2 months and 27 months, originated from diverse geographical locations and did not have pet or animal contact history. Of particular interest were two infants aged 2 months and 10 months who had not begun to consume regular diet and presumably had not been exposed to food-borne organisms. These findings suggest that mcr-1 is already highly prevalent in the environment and transmissible via various routes. Given that all test strains were randomly selected, the actual number of children harbouring mcr-1 positive organisms could be much higher. Minimum inhibitory concentrations of different antibiotics, as determined according to the Clinical & Laboratory Standards Institute guidelines,3Clinical and Laboratory Standards Institute (CSLI)M100-S24. Performance standards for antimicrobial susceptibility testing; twenty-third informational supplement. CSLI, Wayne, PA2014Google Scholar showed that all strains had a colistin minimum inhibitory concentration between 4 and 16 μg/mL, and were resistant to cephalosporins due to coexistence of the CTX-M-15 β-lactamase gene; resistance to levofloxacin, amikacin, and meropenem was also common.TableGenetic and phenotypic characteristics of five mcr-1-positive strains of Escherichia coli, and clinical history of human hosts from whom they were recovered, by patient identification numberHost informationMinimum inhibitory concentration (μg/mL)SexAge (months)DiseaseLocation of dwellingAntibiotic useImipenemCefoperazoneAmikacinLevofloxacinColistin177Male27PneumoniaCityImipenem, cefoperazone–sulbactam<0·25>2562328192Male19PneumoniaVillagePiperacillin2>256>256<0·58238Female2FeverVillageCeftriaxone, azithromycin2128>2562588451Male10Acute bronchitis, acute enteritisCityPiperacillin–tazobactam<0·25881284503Male22EpilepsyVillageCeftriaxone2128225616 Open table in a new tab In summary, our data suggest that human gut flora, especially the E coli subpopulation, have a role in facilitating dissemination of the mcr-1 element by absorbing genetic materials from external sources. The rate of mcr-1 transmission would certainly accelerate as a result of increase in the rate of faecal carriage of this element and clinical use of colistin. We declare no competing interests. Emergence of plasmid-mediated colistin resistance mechanism MCR-1 in animals and human beings in China: a microbiological and molecular biological studyThe 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. Full-Text PDF