首次从湖南猪源大肠杆菌中检出mcr-1阳性IncI2(Delta)质粒

First Report of Colistin-Resistant Escherichia coli Carrying mcr-1 IncI2(Delta)Plasmids from Pigs in Hunan Province,China

近年来,由于抗生素耐药基因的广泛传播及多重耐药细菌的出现,导致抗生素的使用面临严峻挑战,致使毒性较强的多黏菌素又重新引起业界的重视,为此对多黏菌素耐药情况的研究也变得十分重要。为了调查畜牧场中多黏菌素耐药基因mcr-1的流行情况,本研究选择我国湖南省某猪场240份肠肛拭子样品,培养分离鉴定出含有mcr-1耐药基因的大肠杆菌菌株,选取多黏菌素等10种抗菌药物对分离的菌株进行耐药性试验,对所有含mcr-1耐药基因的大肠杆菌阳性株进行全基因组测序(whole-genome sequencing,WGS),采用多位点序列分型(multi-locus sequence typing,MLST)技术进行大肠杆菌的遗传多样性分析。研究结果表明,在分离出的172株大肠杆菌中,来自不同个体的9株携带mcr-1基因的大肠杆菌均表现出多重耐药现象;MLST分析共鉴定出ST10、ST196、ST46和ST5229共4种分型和4种血清型(O83:H5,O16:H7,O16:H51,O9:H4)。生物信息学分析显示,所有阳性菌株均未发现与mcr-1基因传播有关的典型可移动遗传元件ISApl1,但均检出可能会导致mcr-1传播的IV型分泌系统基因。质粒接合转移试验与单倍型的MLST多态性结果表明,mcr-1基因主要以质粒介导的水平传播为主。本研究是国际上首次在猪源细菌中检出常见于人医临床细菌的携带有mcr-1抗性基因的IncI2(Delta)质粒。

The rise of antibiotic resistance has brought renewed attention to older drugs like polymyxins,making it important to control the spread of resistance genes.In this study,we focused on colistin-resistant Escherichia coli strains from a pig farm in Hunan,China.Out of 240 samples,172 E.coli strains were isolated and cultured,PCR was used to identify mcr-1 positive E.coli strains.These strains were tested by ten different antibiotics to check for their drug resistance,and whole-genome sequencing(WGS)was applied to analyze their genetic background.All the nine mcr-1 positive E.coli strains exhibit high levels of multidrug resistance.Four distinct MLST types(ST10,ST196,ST5229,ST46)and 4 serotypes(O83:H5,O16:H7,O16:H51,O9:H4)in the nine strains were identified.Further bioinformatics analyses showed that the ISApl 1 element,which is commonly associated with mcr-1 transmission,was not observed in the present study,while the type IV secretion system genes were detected in all the nine mcr-1 positive E.coli strains.Plasmid conjugation experiments and the presence of polymorphic MLST haplotypes indicated a vertical plasmid-mediated mcr-1 transmission possibility.Notably,our study for the first time uncovered a pig origin IncI2(Delta)plasmid carrying mcr-1 gene in E.coli which is normally presented in the human clinical E.coli strains.