社区分离金黄色葡萄球菌在健康人群中的分布及其分子生物学特点

摘要

目的 调查医科大学学生鼻腔中金黄色葡萄球菌(金葡菌)的定植状况,解析鼻腔定植社区型甲氧两林耐药性金葡菌(MRSA)克隆的分子生物学特点.方法 以无菌棉签从调查对象鼻腔中收集定植菌,鉴定出甲氧西林敏感性金葡菌(MSSA)和MRSA;多重PCR法分型MRSA携带的SCCmec基因岛;PCR测定pvl、seh、tsst1等毒素基因在菌株中的分布;脉冲场凝胶电泳(PFGE)检测MRSA菌株的脉冲场型.结果 2009年977名学生488份样本中鉴定出葡萄球菌,其中凝固酶阴性葡萄球菌(CoNS)和金葡菌分别为364份和124份,MRSA在金葡菌中所占比例为3.4%.2010年调查显示,657名学生中有310份样本鉴定为葡萄球菌属,其中CoNS为195份,金葡菌115份,MRSA在金葡菌中所占比例为7.7%.金葡菌在所有葡萄球菌属中所占比例为29.9%,而MRSA在金葡菌中所占比例为5.1%.MRSA菌株中共鉴定出5种SCCmec基因岛型,其中Ⅳa型最多(10株),为优势SCCmec基因岛类型.PFGE共有11种图谱型,7种(A～G)脉冲场型.10株MRSA均为pvl阳性.结论 1株起源于社区,基因型为Ⅳa SCCmec-pulsotype A且携带pvl毒素基因的特定MRSA克隆在健康大学生中传播.%Objective To investigate the nasal colonization of Staphylococcus (S.) aureus strains among medical university students in Shenyang and to study the molecular epidemiological characteristics of methicillin resistant S. aureus (MRSA) strains. Methods Sterilized nasal swabs were used to collect nasal bacteria from both nares of the students. Nasal specimens were further identified as S. aureus strains, sensitive or resistant to methicillin through a series of tests. Molecular related methods including staphylococcal cassette chromosome mec (SCCmec) typing, pulsed- field gel electrophoresis (PFGE) , coagulase isotyping and minimum inhibitory concentration (MIC) determination etc. were used to characterize the isolates. Prevalence of the panton-valentine leukocidin (pvl) genes (lukS and F-PV) among the isolates was also assessed. Results Staphylococci were found in 488 specimens from 977 participants through the surveillance program, conducted in 2009. Of the 488 specimens being tested, 364 were identified as coagulase-negative staphylococci (CoNS) and 124 as S. aureus. MRSA strain among the S. aureus isolates was accounted for 3.4%. In the surveillance program conducted in 2010, staphylococci grew in 310 specimens fiom 657 participants. Of the 310 specimens tested, 195 were identified as CoNS and 115 as S. aureus. The percentage of MRSA strains among the S. aureus isolates was 7.7%. In total, 239 students carried S.aureus, and the percentage of MRSA carriers among the total specimens tested in this study was 5.1%.Most of the MRSA strains could be classified into one of the five types of SCCmec elements. Type Ⅳ a SCCmec strains were most frequent seen overall (10 isolates). A total of 11 pulsotypes were identified among the MRSA strains and were classified into 7 major groups (A to G) by the mutual correlations of their banding patterns. Ten MRSA strains were identified as pvl positive strains. Conclusion An MRSA clone (Ⅳ a SCCmec pulsotype A) carrying pvl toxin gene was found to be prevalent in the nares of the healthy university students.