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

Abstract

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 (SCC mec) 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%. SCC mec 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%). SCC mec subtypes differed in terms of their frequencies of toxin gene carriage (95.9% in SCC mec II, 74.4% in SCC mec III, and 68.8% in SCC mec IV). Specific SCC mec subtypes frequently harbored particular toxin gene combinations: 77.3% of SCC mec II strains carried sec and tst genes, 48.8% of SCC mec III strains carried sea and see genes, and 46.9% of SCC mec IV carried sea and seb genes. Indeed, the most prevalent combination in MRSA strains, that of sec and tst, was only observed in SCC mec II strains, and these strains failed to show the coexistence of sea and see or sea and seb genes. Thus, the SCC mec 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 SCC mec subtypes.