1株血标本分离的碳青霉烯类、磷霉素耐药大肠埃希菌耐药机制研究

Mechanisms of carbapenem and fosfomycin resistance in an Escherichia coli strain isolated from bloodstream infection

目的探究复旦大学附属华山医院2010年12月血标本分离的1株碳青霉烯类、磷霉素耐药大肠埃希菌的耐药机制及耐药基因可能的传播方式。方法对该株大肠埃希菌进行药敏试验、多位点序列分型(MLST)、耐药基因筛选、质粒分型、PCR mapping基因环境分析。结果该菌株对碳青霉烯类、磷霉素耐药,超广谱β内酰胺酶(ESBL)阳性。MLST属ST46型。碳青霉烯类耐药基因blaKPC-2和磷霉素耐药基因fos A3存在~70 kb接合型质粒上,分别介导碳青霉烯类、磷霉素耐药。β内酰胺酶耐药基因blaTEM、blaCTX-M存在~150 kb接合型质粒上,介导菌株对β内酰胺类药物耐药。PCR mapping结果显示blaKPC-2位于Tn1721-blaKPC-2-Tn3样结构内,fos A3位于IS26-fos A3-IS26移动元件。结论此株来源于血标本菌株携带blaKPC-2、fos A3、blaTEM、blaCTX-M等多种临床常见耐药基因,其耐药机制及耐药基因可能的传播方式,应引起医院感控高度重视。

Objective This study was designed to determine the mechanisms of carbapenem and fosfomycin resistance in an Escherichia coli strain isolated from bloodstream infection in Huashan Hospital, Shanghai in 2010 and the mode of transmission of resistance genes. Methods The Escherichia coli isolate was characterized by antibiotic susceptibility testing, multilocus sequence typing(MLST), molecular identification of resistance genes, plasmid typing and the resistant genetic environment analysis. Results It was found that the isolate was resistant to carbapenem, fosfomycin and produced extended-spectrum β-lactamases. MLST genotyping showed it belonged to ST46. The carbapenem-resistant gene blaKPC-2 and fosfomycin resistant gene fos A3 co-located on the same conjugative plasmid(~70 kb). The β-lactamases gene blaTEM and blaCTX-M located on another conjugative plasmid(~150 kb). PCR mapping showed that blaKPC-2 gene located in the structure Tn1721-blaKPC-2-Tn3 and fos A3 gene located between two IS26 elements. Conclusions This Escherichia coli strain isolated from bloodstream infection carried multiple antibiotic resistant genes, including blaKPC-2, fos A3, blaTEM, and blaCTX-M. More attention should be paid to the mechanisms of antibiotic resistance and transmission of resistance genes in Escherichia coli isolates for better control of hospital infections.