Characterisation of clinical isolates of oxacillin-susceptible mecA-positive Staphylococcus aureus in China from 2009 to 2014

Objectives: The aim of this study was to investigate the prevalence and molecular characteristics of clinical oxacillin-susceptible mecA-positive Staphylococcus aureus (OS-MRSA) isolates in China from July 2009 to June 2014. Methods: A total of 2068 non-duplicate S. aureus isolates were collected from 21 hospitals. Antimicrobial susceptibility testing was performed by the agar dilution method. All OS-MRSA strains were screened for the presence of the genes mecA, mecC and nuc as well as the Panton-Valentine leukocidin gene (pvl). Staphylococcal cassette chromosome mec (SCCmec) typing, staphylococcal protein A (spa) typing and multilocus sequence typing (MLST) were performed to analyse the isolate genotypes. Results: A total of 34 S. aureus isolates were mecA-positive but were susceptible to oxacillin [minimum inhibitory concentration (MIC) <= 2 mg/L]. All OS-MRSA isolates were resistant to cefoxitin and most were also multiresistant to other antibiotics besides beta-lactams. Among the 34 OS-MRSA isolates, nine spa and three SCCmec types were detected and, combined with MLST, ST338/59-t437-SCCmecV (47%; 16/34) was the predominant clone. In addition, 17 strains (50%) carried the pvl gene. Conclusions: The most frequent clone of OS-MRSA isolates in China was ST338-t437-SCCmecV. Most of the OS-MRSA isolates were susceptible to the majority of antibacterial agents except macrolides, clindamycin and chloramphenicol. (C) 2017 Published by Elsevier Ltd on behalf of International Society for Chemotherapy of Infection and Cancer.