Characterization of a PVL-negative community-acquired methicillin-resistant Staphylococcus aureus strain of sequence type 88 in China

Sequence type 88 community -acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) strain SR434, isolated from an outpatient with skin and soft tissue infection, was subjected to whole genome sequencing, antimicrobial susceptibility testing, mouse skin infection model and hemolysis analysis to identify its virulence and resistance determinants. MRSA strain SR434 is resistant to clindamycin, erythromycin and fosfomycin. Four plasmids with resistance genes were identified in this strain, including a 20,658 bp NaZ-carrying plasmid, a 2473 bp ermC-carrying plasmid, a 2622 bp fosB7-carrying- plasmid (86% identity with plasmid in a ST2590 MRSA strain) and a 4817 bp lnuA -carrying plasmid (99% identity with pLNU4 from bovine coagulase-nagetive Staphylococci). This strain contains staphylococcal cassette chromosome mec type IV and does not contain arginine catabolic mobile element or Panton-Valentine-Leukocidin. SR434 harbors genomic islands vSa alpha, vSa beta, vSa gamma and Phi Sa3 and pathogenicity islands vSa2 that carries genes encoding toxic shock syndrome toxin 1, superantigen enterotoxin C and superantigen enterotoxin L. Mouse skin infection model results show that SR434 had similar virulence potential causing invasive skin infection as a PVL-negative epidemic Korea clone HL1 (ST72). CA-MRSA strain of ST88 lineage might be a great concern for its high virulence. PVL has limited contribution to virulence phenotype among this lineage.