Staphylococcus aureus Proteins Implicated in the Reduced Virulence of sarA and sarA/agr Mutants in Osteomyelitis

Using a murine osteomyelitis model, we recently demonstrated that <i>Staphylococcus aureus sarA</i> and <i>sarA/agr</i> mutants generated in the USA300 strain LAC are attenuated to a greater extent than an isogenic <i>agr</i> mutant and that this can be attributed to a significant extent to the increased production of extracellular proteases in both mutants. Based on this, we used a mass-based proteomics approach to compare the proteomes of LAC, its isogenic <i>agr</i>, <i>sarA</i>, and <i>sarA/agr</i> mutants, and isogenic derivatives of all four of these strains unable to produce the extracellular proteases aureolysin, SspA, SspB, ScpA, or SplA-F. This allowed us to identify proteins that were present in reduced amounts in <i>sarA</i>, and <i>sarA</i>/<i>agr</i> mutants owing to the increased production of extracellular proteases. A total of 1039 proteins were detected in conditioned media (CM) from overnight cultures of LAC, and protease-mediated degradation was shown to contribute to the reduced abundance of 224 of these (21.6%) in CM from the <i>sarA</i> and <i>sarA/agr</i> mutants. Among these were specific proteins previously implicated in the pathogenesis and therapeutic recalcitrance of <i>S. aureus</i> osteomyelitis. This demonstrates that the ability of <i>sarA</i> to limit protease production plays a key role in post-translational remodeling of the <i>S. aureus</i> proteome to a degree that can be correlated with reduced virulence in our osteomyelitis model, and that it does so irrespective of the functional status of <i>agr</i>. This also suggests that at least some of these 224 proteins may be viable targets for prophylactic or therapeutic intervention.