Hyperexpression of α-hemolysin explains enhanced virulence of sequence type 93 community-associated methicillin-resistant Staphylococcus aureus

Abstract

BackgroundThe 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.ResultsHere, 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.ConclusionsThese 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.

Staphylococcus aureus Infections: Epidemiology, Pathophysiology, Clinical Manifestations, and Management

“…In a mouse model, less severe infection ensued after inoculation with agr-deleted S. aureus strains (310). Similarly, clinical ST93 strains with agr mutations produce less alpha-hemolysin and are less virulent than wild-type strains (298).…”

“…More recently, it was discovered that alpha-hemolysin interacts with the ADAM10 receptor, and ADAM10-deficient mice are protected from severe skin infection (295). In the virulent Australian sequence type 93 (ST93) MRSA clone (296,297), high levels of alpha-hemolysin have been associated with more severe cutaneous lesions (298). Alpha-hemolysin also appears to contribute to the penetration of keratinocytes in skin infection (299).…”

Genetic and Molecular Predictors of High Vancomycin MIC in Staphylococcus aureus Bacteremia Isolates

“…The presence of agr dysfunction was defined as an absence or severe depression of delta-hemolysin production (21). The positive control was JKD6159, a fully sequenced S. aureus reference isolate known to have a functional agr operon, and the negative control was TPS3105, a sequenced S. aureus isolate with defective agr function (22).…”

Natural mutations in a Staphylococcus aureus virulence regulator attenuate cytotoxicity but permit bacteremia and abscess formation

“…This model is compatible with the function of other AFTR members, which, in other bacterial genera, regulate carbon metabolism, stress responses, and virulence in response to changing environmental conditions such as antibiotic use and stress (56,57). In S. aureus, the AFTRs rbf, rsr, and aryK promote biofilm formation (58), modulate sarR and agr in a skin infection model (59), and potentiate toxin expression and virulence (60), respectively.…”