Prevalence and Genetic Diversity of Staphylococcal Enterotoxin (-Like) Genes sey, selw, selx, selz, sel26 and sel27 in Community-Acquired Methicillin-Resistant Staphylococcus aureus

Staphylococcal enterotoxins (SEs) are virulence factors ofStaphylococcus aureusassociated with various toxic diseases due to their emetic and superantigenic activities. Although at least 27 SE(-like) genes have been identified inS. aureusto date, the newly identified SE(-like) genes have not yet been well characterized by their epidemiological features. In this study, the prevalence and genetic diversity of SE geneseyand SE-like genesselw,selx,selz,sel26, andsel27were investigated for 624 clinical isolates of community-acquired methicillin-resistantS. aureus(CA-MRSA). The most prevalent SE(-like) gene wasselw(92.9%), followed byselx(85.6%),sey(35.4%) andselz(5.6%), whilesel26andsel27were not detected. Phylogenetically,sey,selw,selx, andselzwere discriminated into 7, 10, 16, and 9 subtypes (groups), respectively. Among these subtypes,seywas the most conserved and showed the highest sequence identity (>98.8%), followed byselzandselx. The SE-like geneselwwas the most divergent, and four out of ten genetic groups contained pseudogenes that may encode truncated product. Individual subtypes of SE(-like) genes were generally found in isolates with specific genotypes/lineages ofS. aureus. This study revealed the putative ubiquity ofselwandselxand the prevalence ofseyandselzin some specific lineages (e.g., ST121) in CA-MRSA, suggesting a potential role of these newly described SEs(-like) in pathogenicity.