浙江省东阳地区大肠埃希菌mcr-1的检测及流行病学研究

Detection and epidemiology of mcr-1-positive Escherichia coil strains in Dongyang area of Zhejiang Province

目的研究浙江省东阳地区临床分离大肠埃希菌多粘菌素耐药现状和质粒介导多粘菌素耐药基因mcr-1的携带情况，了解携带mcr-1的大肠埃希菌菌株流行特征，为当地临床医生防控mcr-1携带菌株的扩散和传播提供理论依据。方法收集浙江省东阳市人民医院2016年1月至12月临床分离的非重复315株大肠埃希菌，所有菌株分离自血液、尿液和呼吸道标本等。采用PCR检测质粒介导的多粘菌素耐药基因mcr-1、β-内酰胺酶和碳青霉烯类耐药基因；微量肉汤稀释法测定抗生素对mcr-1阳性菌株的最低抑菌浓度；采用接合试验检测mcr-1基因是否位于可转移质粒上；通过多位点序列分型（multilocus sequence typing, MLST）对mcr-1阳性菌株进行分子分型。结果在315株大肠埃希菌中，共5株检测出mcr-1，阳性率为1.6%。5株mcr-1阳性大肠埃希菌中，2株同时检测到β-内酰胺酶耐药基因，均为blaTEM-1和blaCTX-M-14，此2株大肠埃希菌对一、二、三代头孢菌素均耐药，仅1株对头孢吡肟耐药。所有5株mcr-1阳性大肠埃希菌对环丙沙星及左氧氟沙星均敏感，对替卡西林/克拉维酸均耐药。未检测到碳青霉烯类耐药基因。5株mcr-1阳性大肠埃希菌接合成功1株。MLST分型结果显示有4种ST型，其中ST131型有2株，ST43、ST69、ST349各1株。结论多粘菌素耐药基因mcr-1在浙江省东阳地区临床分离的大肠埃希菌中检测率较低，仅为1.6%，说明该基因在东阳地区还没有形成流行趋势，只是零星散发式存在。但已经发现mcr-1基因与β-内酰胺酶耐药基因共存的现象，提示临床应加强对抗生素使用的控制，防止多重耐药菌株的扩散。

ObjectiveTo investigate the prevalence of mcr-1 gene, a plasmid-mediated polymyxin resistance gene, in Escherichia coli （E.coli） strains isolated in Dongyang of Zhejiang Province and to understand the epidemiological characteristics of E. coli strains carrying mcr-1 gene in order to provide local clinicians with a theoretical basis for prevention and control of the spread of mcr-1-bearing E. coli strains.MethodsA total of 315 E. coli strains were collected in the People′s Hospital of Dongyang, Zhejiang Province from January to December 2016. All strains were isolated from specimens of blood, urine, respiratory tract, etc. PCR was performed to detect the genes confering resistance to polymyxin （mcr-1 gene）, β-lactamase and carbapenem. Minimal inhibitory concentrations （MIC） of antibiotics against mcr-1-positive strains were determined by micro-broth dilution method. Conjugation test was performed to confirm whether the mcr-1 gene was located on the transferable plasmid. Multilocus sequence typing （MLST） was used for molecular typing of mcr-1-positive strains.ResultsFive mcr-1-positive strains were identified from 315 E. coli strains with a positive rate of 1.6%. Two out of the five mcr-1-positive E. coli strains contained β-lactamase resistance genes, blaTEM-1 and blaCTX-M-14. Both of them were resistant to the first, second and third generation of cephalosporins and one was also resistant to cefepime. All of the five mcr-1-positive E. coli strains were sensitive to ciprofloxacin and levofloxacin, but resistant to ticarcillin/clavulanic acid. No carbapenem resistance genes were detected. One transconjugant was successfully obtained by transconjugation assay. MLST analysis showed that a total of four sequence types were identified, including ST131 （two strains）, ST43 （one strain）, ST69 （one strain） and ST349 （one strain）.ConclusionOnly 1.6% of all E. coli strains isolated in Dongyang area of Zhejiang Province carry mcr-1 gene, indicating that there is no epidemic of mcr-1 gene-positive E. coli infection. The coexistence of mcr-1 gene and β-lactamase resistance genes in E. coli strains isolated in Dongyang suggests that local clinicians should avoid antibiotic abuse to prevent the spread of drug-resistant E. coli.