Background: The aim of this study was to better understand methicillin-resistant Staphylococcus aureus (MRSA) at the molecular level by investigating the genotypic characteristics and evolutionary patterns of MRSA clones in Shenyang, China.
Methods: We analyzed the molecular epidemiology of 60 MRSA isolates in Shenyang, China, between 2002 and 2008, using pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) typing, and S. aureus protein A (spa) typing. They were examined for their antimicrobial susceptibilities.
Results: Among the 60 isolates, ST239 was identified most frequently (34 isolates; 58%), followed by ST5 (20 isolates; 34%). Nine spa types were obtained and 4 PFGE strain families (A, B, C, and D) were resolved. Spa type t030, which corresponded to PFGE genotypes A1, A3, and A4, constituted 45% (27/60) of all isolates; spa type t037, which corresponded to PFGE type A2, accounted for 13% (8/60) of all isolates. These 2 spa genotypes belonged to ST239 and carried SCCmec type III. Isolates genotyped as spa type t002 comprised 27% (16/60) of the study set and included isolates typed as PFGE B1 and B2, ST5, and SCCmec II. Most of MRSA isolates belonging to ST239 were susceptible to trimethoprim-sulfamethoxazole. The minimum inhibitory concentration (MIC50) of vancomycin among MRSA isolates belonging to ST5 (2 mg/l) was higher than that for other isolates (1 mg/l).
Conclusions: These data document 2 major epidemic MRSA clones in Shenyang, China: ST239-MRSA-SCCmec type III-t037/t030 and ST5-MRSA-SCCmec type II-t002.