Emergence Of Plasmid-Mediated Colistin Resistance Gene Mcr-1 In Enterobacteriacea

Recently, the multidrug resistant Gram-negative bacilli has been increasing year by year,resulting in the limited options for effective antibiotic therpay.Polymyxins are reintroduced to clinic that are the last-resort antibiotics for the treatment of multidrug-resistant, Gram-negative bacterial infections.The polymyxins resistance has occurred via chromosoma.We report the emergence of transmissible, plasmid-mediated colistin resistance in the form of MCR-1.One E coli strain(isolate from a pig,Shanghai, in2013,designated SHP45, minimum inhibitory concentration[MIC] of colistin of 8 mg/L)was randomly selected for research object.pmr AB, pho PQ, and mgr B genes of SHP45 were amplified and sequenced with the primer of mutation detection,without any mutation genes related to polymyxins resistance.The plamisd p HNSHP45,carrying colistin resistance,could be successfully transferred to recipient strain at a frequency of 10-1~10-3cells per recipient cell by conjugation.experiment.p HNSHP45 could be transferred via conjugation or transformation into K pneumoniae,increasing in colistin’s minimum inhibitory concentrations.The plamisd p HNSHP45 was fully sequenced using high throughput sequencing,revealed a plasmid 64 015 bp in size with an average G+C content of 43.0% and possesses a typical Inc I2-type backbone.In addition, a 1626-bp open reading frame that postulate and was named mcr-1 was found located downstream of an insertion sequence ISApl1,postulate that the plamisd p HNSHP45 get mcr-1 from exogenous gene.The deduced aminoacid sequence of the mcr-1 gene product,MCR-1,aligned closely withphosphoethanolaminetransferases(about 60% identity).Thus, the function of MCR-1 was confirmed by analyzing lipid A with mass spectrometry.The stability of p HNSHP45 was examined by determined by S1 pulsed-field gel electrophoresis(PFGE) and hybridization. After 14 days of passaging either with or without colistin(2 mg/L),the plasmid was stable in both E coli C600(p NHSHP45) and in strain E coli SHP45.PCR were used to determine the dissemination and occurrence of the mcr-1 in E coli isolates of animals.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.It indicated that mcr-1 has disseminated broadly in animals,and the proportion of positive samples increased from year to year.We report the emergence of the first plasmid-mediated polymyxin resistance gene,mcr-1. mcr-1 was located on Inc I2 type plasmid and downstream of an insertion sequence ISAp I1.MCR-1 is a member of the phosphoethanolamine transferase enzyme family, mediated polymyxin resistance via the modification of phosphoethanolamine with lipid A moiety of bacterial cell membrane.mcr-1 gene has been widespread in E coli from food animals and food, located on conjugative plasmid, be extremely easy to spread out. It explains that the currently domestic polymyxin resistance rises rapidly in molecular mechanism.It will provide a foundation for the risk assessment of polymyxins in animals.