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

Kyra Yl Chua,Geoffrey W Coombs,Kellie L Tuck,Ian R Monk,Justin Stepnell,Ya-Hsun Lin,Torsten Seemann,John K Davies,Benjamin P Howden,Jessica L Porter,Timothy P Stinear

doi:10.1186/1471-2180-14-31

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.

Highlights

The community-associated methicillin-resistant S. aureus (CA-MRSA) ST93 clone is becoming dominant in Australia and is clinically highly virulent
The emergence of CA-MRSA is a major public health issue, and there is a clear need to understand the basis for both virulence and transmission of global clones of CAMRSA
Exotoxin expression in ST93 CA-MRSA strains Staphylococcus aureus expresses a wide range of exotoxins that may contribute to virulence

Summary

Introduction

The community-associated methicillin-resistant S. aureus (CA-MRSA) ST93 clone is becoming dominant in Australia and is clinically highly virulent. Sepsis and skin infection models demonstrate that ST93 CA-MRSA is the most virulent global clone of S. aureus tested to date. Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is an emerging global problem with very similar clinical presentations across different clones, despite significant genetic diversity [1]. The importance of PVL is likely to be dependent on the site of infection. In the rabbit pneumonia model, PVL has been demonstrated to have a clear role in mediating severe lung necrosis and inflammation [3]. In skin infection, even in the rabbit model, its role remains less clear [4,5]

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