21Background: Staphylococcus aureus (S. aureus) is a major human pathogen owing to 22 its arsenal of virulence factors, as well as its acquisition of multi-antibiotic resistance.
23Here we report the identification of a Streptolysin S (SLS) like biosynthetic gene cluster 24 in a highly virulent community-acquired methicillin resistant S. aureus (MRSA) isolate, 25 JKD6159. Examination of the SLS-like gene cluster in JKD6159 shows significant 26 homology and gene organization to the SLS-associated biosynthetic gene (sag) cluster 27 responsible for the production of the major hemolysin SLS in Group A Streptococcus. 28 Results: We took a comprehensive approach to elucidating the putative role of the sag 29 gene cluster in JKD6159 by constructing a mutant in which one of the biosynthesis 30 genes (sagB homologue) was deleted in the parent JKD6159 strain. Assays to evaluate 31 bacterial gene regulation, biofilm formation, antimicrobial activity, as well as complete 32 host cell response profile and comparative in vivo infections in Balb/Cj mice were 33 conducted. 34 Conclusions: Although no significant phenotypic changes were observed in our 35assays, we postulate that the SLS-like toxin produced by this strain of S. aureus may be 36 a highly specialized virulence factor utilized in specific environments for selective 37 advantage; studies to better understand the role of this newly discovered virulence 38 factor in S. aureus warrant further investigation. 39
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