The molecular characteristics and virulence factor of Methicillin-resistant Staphylococcus aureus isolatedfrom pediatric patients / 中华传染病杂志

ABSTRACT

Objective To investigate the molecular characteristic,the virulence factors and antimicrobial resistance of Methicillin-resistant Staphylococcus aureus (MRSA) isolated from pediatric patients.Methods Ninety-eight non-duplicate strains of and 49 non-duplicate strains of Methicillinsusceptible Staphylococcus aureus (MSSA) isolated from the three children's hospitals in Shanghai in 2008 were investigated.Panton-valentine leukocidin (PVL) gene was detected by polymerase chain reaction (PCR).The genotypes of staphylococcal cassette chromosome mec (SCCmec) of the MRSA isolates were confirmed by multiplex PCR.The sequence type (ST) of each strain was determined by multilocus sequence typing (MLST),and the algorithm eBURST was used to identify groups of clonal complex (CC).The minimal inhibitory concentrations (MIC) of fourteen antibiotics for all isolates were determined by agar dilution method.Results Among 98 isolates of MRSA,the positive rate of PVL genes was 6.1％ (6/98).In contrast,the positive rate of PVL genes was 4.1％ (2/48) of the MSSA strains.Among 98 isolates of MRSA,4.1％ (4/98),23.5％ (23/98),53.0％ (52/98) and 15.3％ (15/98) of the strains harboured SCCmec types Ⅱ,Ⅲ,Ⅳ and Ⅴ,respectively. The remaining four isolates (4.1 ％) presented a unique SCCmec pattern that could not be classified to any known types by the employed typing assays.Combining the ST and SCCmec type,the predominant clones were ST59-SCCmec Ⅳ (30 strains) and ST239-SCCmec Ⅲ (23 strains),followed by ST5-SCCmecⅣ and ST1-SCCmecⅣ (8 strains for each clone),ST239-SCCmec Ⅴ (6 strains),ST88-SCCmecⅤ (5 strains),ST5 SCCmecⅡ (4 strains),ST59-SCCmec Ⅴ (3 strains),ST8-SCCmecⅣ and ST88-SCCmecⅣ (2 strains for each clone),ST22-SCCmecⅣ,ST910-SCCmecⅣ and S45-SCCmec Ⅴ (1 strain for each clone),eBURST analysis distributed the MRSA isolates into several CC.ST8 and ST239 belonged to ST8 CC,ST1 belonged to ST15 CC,ST910 belonged to ST 30 CC,ST59,ST5,ST88,ST45,ST22,ST9 and ST7 were the origin of their own CC.The results of MIC showed that the 67 strains of MRSA harboring SCCmec type Ⅳ or SCCmec type Ⅴ were more susceptible to various non-β-lactam antibiotics than 27 strains of MRSA harboring SCCmec type Ⅱ or SCCmec type Ⅲ,and no vancomycin-resistant strain was found.Conclusions In three children's hospitals in Shanghai,the PVL gene-positive rate of MRSA isolates is relatively low,SCCmec type Ⅳ and SCCmec type Ⅴ could spread among hospitals to cause a small scale epidemic and have a variety of ST.