Supplementary Material for: Methionine Sulfoxide Reductases Protect against Oxidative Stress in <b><i>Staphylococcus aureus</i></b> Encountering Exogenous Oxidants and Human Neutrophils

To establish infection successfully, <i>Staphylococcus aureus</i> must evade clearance by polymorphonuclear neutrophils (PMN). We studied the expression and regulation of the methionine sulfoxide reductases (Msr) that are involved in the repair of oxidized staphylococcal proteins and investigated their influence on the fate of <i>S. aureus </i>exposed to oxidants or PMN. We evaluated a mutant deficient in <i>msrA1 </i>and <i>msrB </i>for susceptibility to hydrogen peroxide, hypochlorous acid and PMN. The expression of <i>msrA1</i> in wild-type bacteria ingested by human PMN was assessed by real-time PCR. The regulation of <i>msr </i>was studied by screening a library of two-component regulatory system (TCS) mutants for altered <i>msr</i> responses. Relative to the wild-type bacteria, bacteria deficient in Msr were more susceptible to oxidants and PMN. Upregulation of staphylococcal <i>msrA1 </i>occurred within the phagosomes of normal PMN and PMN deficient in NADPH oxidase activity. Furthermore, PMN granule-rich extract stimulated the upregulation of <i>msrA1.</i> Modulation of <i>msrA1</i> within PMN was shown to be partly dependent on the VraSR TCS. Msr contributes to staphylococcal responses to oxidative attack and PMN. Our study highlights a novel interaction between the oxidative protein repair pathway and the VraSR TCS that is involved in cell wall homeostasis