耐甲氧西林金黄色葡萄球菌的基因型分布及在不同遗传基因背景下的耐药谱分析

Genotype distribution of methicillin-resistant Staphylococcus aureus and analysis on resistance pattern under different genetic backgrounds

目的:调查某三甲医院耐甲氧西林金黄色葡萄球菌(MRSA)的基因型分布,探讨菌株各分子分型间的相关性,并构建不同遗传背景下的耐药谱模型。方法:选取来源于医院25个科室的金黄色葡萄球菌(S.aureus)共计204株,采用全自动VITEK 2 Compact细菌鉴定和药敏分析仪及E-test条检测菌株的抗菌药物敏感性,以聚合酶链式反应(PCR)法检测mecA基因作为确证实验,比较头孢西丁(FOX)和(或)苯唑西林(OXA)作为表型检测方法筛选MRSA的能力。采用PCR法检测MRSA菌株的分子分型,包括S.aureus A蛋白分型(spa)、附属基因调节器分组(agr)、多位点序列分型(MLST)和S.aureus染色体盒mec分型(SCCmec)。结合药物敏感实验和分子分型结果,构建不同遗传背景下的耐药谱。结果:通过检测mecA基因共获得39株MRSA。通过检测FOX和OXA共获得51株表型MRSA。spa分型中,共鉴定出包括5种新型(t20226、t20227、t20228、t20229和t20230)在内的57种不同型别,主要为t309(30.9%)、t078(11.8%)和t437(11.8%)。agr分型,94.9%的MRSA属于agrⅠ。MLST分析MRSA种群,ST59克隆(61.5%)最流行,其次为ST72(20.5%)。87.2%的MRSA携带Ⅳ型SCCmec,其中亚型Ⅳa 24株,亚型ⅣF 10株。结论:MRSA的主要基因型为ST59-t437-agrⅠ-Ⅳa,其耐药谱主要表现为FOX-OXA-青霉素(PEN)-红霉素(ERY)-克林霉素(CLI)。

Objective:To discuss the genotype distribution of methicillin-resistant Staphylococcus aureus(MRSA)in a tertiary hospital and to discuss the correlation among different molecular types of the strains,and to construct the resistance profile model under different genetic backgrounds.Methods:A total of 204 strains of Staphylococcus aureus(S.aureus)from 25 departments of the hospital were selected.The automatic VITEK 2 Compact system and E-test strips were used to detect the antimicrobial susceptibility of the strains.The detection of mecA gene by the polymerase chain reaction(PCR)method was used as the confirmatory experiment,the abilities of cefoxitin(FOX)and(or)oxacillin(OXA)were compared as phenotypic detection methods to screen MRSA.The molecular typing of MRSA strains was carried out by PCR method,including Staphylococcal protein A gene(spa)determination,accessory gene regulator(agr)typing,multilocus sequence typing(MLST),and staphylococcal chromosomal cassettes mec(SCCmec)typing.The resistance profile was constructed combing with antimicrobial susceptibility tests results and molecular typing results.Results:A total of 39 MRSA strains were obtained by detecting the mecA gene.A total of 51 phenotypic MRSA strains were identified by testing FOX and OXA.In spa typing,57 different types were identified,including 5 new types(t20226,t20227,t20228,t20229,and t20230),with the main types being t309(30.9%),t078(11.8%),and t437(11.8%).In agr typing,94.9%of MRSA belonged to agrⅠ.The MLST analysis results of MRSA populations showed that ST59 clone(61.5%)was the most prevalent,followed by ST72(20.5%).A total of 87.2%of MRSA carried typeⅣSCCmec,with subtypesⅣa accounting for 24 strains and subtypeⅣF accounting for 10 strains.Conclusion:The main genotype of MRSA is ST59-t437-agrⅠ-Ⅳa and its resistance profile is primarily characterized by resistance to FOX-OXA-penicillin(PEN)-erythromycin(ERY)-clindamycin(CLI).