The ability to treat infections caused by Staphylococcus aureus is increasingly compromised by the emergence of antibiotic resistant strains, most notably methicillin-resistant S. aureus (MRSA). This is perhaps most evident in the increasing prevalence of MRSA even among isolates causing community-acquired infections, with USA300 clonal lineage being the primary cause of complicated S. aureus infections. Based on this, we have begun to investigate the mechanistic basis for the enhanced virulence of USA300 isolates. During the course of studies preceding this work, we discovered that mutation of the staphylococcal accessory regulator (sarA) in USA300 lineage limits biofilm formation to a degree that can be correlated with increased antibiotic susceptibility in vitro and in vivo. Hence, sarA would be a viable target for the development of therapeutic agents, working as adjunct therapy to enhance the efficacy of conventional antimicrobial agents. However, sarA as a global regulator impacts production of many more virulence factors than biofilm itself. Therefore, it is necessary to fully define the role of sarA in other clinically relevant contexts, such as the regulation of other major virulence factors, before the development of such an agent. In this work we demonstrate that mutation of sarA in USA300 limits the accumulation of alpha toxin and phenol-soluble modulins (PSMs), the two virulence factors, proposed to be the primary contributors to the enhanced virulence of this isolate. Degradation assays and experiments done with protease inhibitors suggested that this was due to the increased production of extracellular proteases rather than differences associated with the impact of sarA on transcription of the target gene (hla) or the accessory gene regulator ( agr). To assess the relevance of this in vivo, we used murine models of implant-associated infection and S. aureus bacteremia to compare virulence of the USA300 strain, its isogenic sarA mutant, and derivatives of each of these strains with mutations in all of the genes encoding recognized extracellular proteases. The sarA mutant was attenuated in both models, and this was reversed to a significant degree by eliminating production of extracellular proteases. To examine the mechanistic basis for this, we compared the protein profiles of these strains and identified 253 proteins where accumulation was reduced in the sarA mutant by comparison to both the parent strain and its isogenic sarA/protease mutant.
|Advisor:||Smeltzer, Mark S.|
|Commitee:||Blevins, Jon S., Lee, Chia Y., Moran, Jeffery H., Tackett, Alan J.|
|School:||University of Arkansas for Medical Sciences|
|Department:||Microbiology and Immunology|
|School Location:||United States -- Arkansas|
|Source:||DAI-B 74/06(E), Dissertation Abstracts International|
|Subjects:||Icelandic & Scandinavian literature, Microbiology|
|Keywords:||Alpha toxin, Methicillin resistance, Proteases, Sara, Staphylococcus aureus, Virulence factors|
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