title: Hyperexpression of α-hemolysin explains enhanced virulence of sequence type 93 community-associated methicillin-resistant Staphylococcus aureus.
abstract: BACKGROUND
  The community-associated methicillin-resistant S. aureus (CA-MRSA) ST93 clone is becoming dominant in Australia and is clinically highly virulent. In addition, sepsis and skin infection models demonstrate that ST93 CA-MRSA is the most virulent global clone of S. aureus tested to date. While the determinants of virulence have been studied in other clones of CA-MRSA, the basis for hypervirulence in ST93 CA-MRSA has not been defined.
  
  
  RESULTS
  Here, using a geographically and temporally dispersed collection of ST93 isolates we demonstrate that the ST93 population hyperexpresses key CA-MRSA exotoxins, in particular α-hemolysin, in comparison to other global clones. Gene deletion and complementation studies, and virulence comparisons in a murine skin infection model, showed unequivocally that increased expression of α-hemolysin is the key staphylococcal virulence determinant for this clone. Genome sequencing and comparative genomics of strains with divergent exotoxin profiles demonstrated that, like other S. aureus clones, the quorum sensing agr system is the master regulator of toxin expression and virulence in ST93 CA-MRSA. However, we also identified a previously uncharacterized AraC/XylS family regulator (AryK) that potentiates toxin expression and virulence in S. aureus.
  
  
  CONCLUSIONS
  These data demonstrate that hyperexpression of α-hemolysin mediates enhanced virulence in ST93 CA-MRSA, and additional control of exotoxin production, in particular α-hemolysin, mediated by regulatory systems other than agr have the potential to fine-tune virulence in CA-MRSA.
authors: Kyra Y L
authors: KY
authors: Chua
authors: Ian R
authors: IR
authors: Monk
authors: Ya-Hsun
authors: YH
authors: Lin
authors: Torsten
authors: T
authors: Seemann
authors: Kellie L
authors: KL
authors: Tuck
authors: Jessica L
authors: JL
authors: Porter
authors: Justin
authors: J
authors: Stepnell
authors: Geoffrey W
authors: GW
authors: Coombs
authors: John K
authors: JK
authors: Davies
authors: Timothy P
authors: TP
authors: Stinear
authors: Department of Microbiology and Immunology, University of Melbourne, Melbourne, Victoria 3052, Australia. benjamin.howden@austin.org.au.
authors: Benjamin P
authors: BP
authors: Howden
mesh_terms: D000818:Animals; D001315:Australia; D001427:Bacterial Toxins / Q000096:biosynthesis / Q000235:genetics; D017714:Community-Acquired Infections / Q000382:microbiology* / Q000473:pathology*; D004195:Disease Models, Animal; D005260:Female; D017353:Gene Deletion; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D005816:Genetic Complementation Test; D016680:Genome, Bacterial; D006460:Hemolysin Proteins / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification / Q000472:pathogenicity*; D051379:Mice; D008807:Mice, Inbred BALB C; D017422:Sequence Analysis, DNA; D013207:Staphylococcal Skin Infections / Q000382:microbiology* / Q000473:pathology*
chemical_list: D001427:Bacterial Toxins; D006460:Hemolysin Proteins