Antimicrobial Resistance, SCC, Virulence and Genotypes of MRSA in Southern China for 7 Years: Filling the Gap of Molecular Epidemiology.

As the prevalence of infections is of worldwide concern, phenotype and genotype in prevalent MRSA strains require longitudinal investigation. In this study, the antibiotic resistance, virulence gene acquisition, and molecular type were determined on a large scale of nosocomial strains in Southern China during 2009-2015. Bacterial identification and antimicrobial susceptibility to 10 antibiotics were tested by Vitek-2. Virulence genes encoding staphylococcal enterotoxins (SEA, SEB, SEC, SED, and SEE), exfoliative toxins (ETA and ETB), Panton-Valentine leukocidin (PVL), and toxic shock syndrome toxin (TSST) were detected by PCR, with SCC typing also conducted by multiplex PCR strategy. Genotypes were discriminated by MLST and spaA typing. MLST was performed by amplification of the internal region of seven housekeeping genes. PCR amplification targeting the gene was performed for spa typing. No resistance to vancomycin, linezolid, or quinupristin and increase in the resistance to trimethoprim/sulfamethoxazole (55.5%) were identified. A total of nine SCC types and subtypes, thirteen STs clustered into thirteen types were identified, with ST239-SCC III-t037 presenting the predominant methicillin-resistant (MRSA) clone. Typically, SCC type IX and ST546 were emergent types in China. Isolates positive for both and genes and for both and genes were also identified. Important findings in this study include: firstly, we have provided comprehensive knowledge on the molecular epidemiology of MRSA in Southern China which fills the gap since 2006 or 2010 from previous studies. Secondly, we have presented the correlation between virulence factors (four major groups) and genotypes (SCC, ST and types). Thirdly, we have shown evidence for earliest emergence of type I SCC from 2012, type VI from 2009 and type XI from 2012 in MRSA from Southern China.