Association between the methicillin resistance of clinical isolates of Staphylococcus aureus, their staphylococcal cassette chromosome mec (SCCmec) subtype classification, and their toxin gene profiles.

Virulence and antimicrobial resistance are important determinators of the clinical manifestations and of the treatments of bacterial infections. Here, we studied the associations between the methicillin resistance of clinical Staphylococcus aureus isolates, their classifications as particular staphylococcal cassette chromosome mec (SCCmec) subtypes, and their toxin gene profiles. In total, 252 S. aureus isolates were collected from 13 healthcare facilities in 6 Korean provinces. The overall prevalence of methicillin-resistant S. aureus (MRSA) was 63%. SCCmec typing and toxin gene analysis were performed by multiplex polymerase chain reaction. One or more staphylococcal toxin genes were found in 190 (75.4%) strains. Methicillin-resistant S. aureus strains carried toxin genes more frequently than methicillin-susceptible S. aureus strains (85.5% versus 53.8%). SCCmec subtypes differed in terms of their frequencies of toxin gene carriage (95.9% in SCCmec II, 74.4% in SCCmec III, and 68.8% in SCCmec IV). Specific SCCmec subtypes frequently harbored particular toxin gene combinations: 77.3% of SCCmec II strains carried sec and tst genes, 48.8% of SCCmec III strains carried sea and see genes, and 46.9% of SCCmec IV carried sea and seb genes. Indeed, the most prevalent combination in MRSA strains, that of sec and tst, was only observed in SCCmec II strains, and these strains failed to show the coexistence of sea and see or sea and seb genes. Thus, the SCCmec subtypes of S. aureus revealed specific staphylococcal toxin profiles. We revealed that certain staphylococcal toxin gene profiles are associated not only with the methicillin resistance of S. aureus but also with their SCCmec subtypes.