SENSING AND ADAPTING TO THE NEUTROPHIL: SAER/S DEPENDENT EVASION STRATEGIES USED BY STAPHYLOCOCCUS AUREUS

Staphylococcus aureus (S. aureus) is one of the most frequent causes of bacterial infections in the U.S. and isresponsible for diverse types of infections ranging in severity from mild to fatal in both hospital and communitysettings. In the community, S. aureus typically causes skin-and-soft-tissue infections with an estimated 12 ?13 million outpatient visits per-year (in the U.S.) but can also cause severe manifestations including necrotizingfasciitis and sepsis in individuals with no underlying risk. One of the most clinically significant aspects of S.aureus infections is the high prevalence of drug resistance and the innate ability for S. aureus to developresistance to antibiotics making it very difficult to develop therapeutics that will have potential for long-termefficacy on S. aureus. The research proposed in this application will broaden our understanding of host-pathogen interactions, providing the foundation for future studies aimed at the intelligent design of novelvaccines and therapies to treat bacterial infection. Research that defines protective host immune responsesand the mechanisms used by pathogens to undermine them can be translated to new treatment strategies thatwill improve public health. Based on strong published and preliminary findings using mouse models ofinfection and human neutrophil assays, we have identified specific host and pathogen factors that will beinvestigated to determine their precise roles in pathogenesis. To that end, this project will study how S. aureususes the SaeR/S two-component gene regulatory system to evade innate immunity. The SaeR/S system isessential for evasion of neutrophil killing; however, exact mechanisms dependent on SaeR/S resulting inneutrophil dysfunction are not defined. Three specific aims will test the hypothesis that S. aureus uses theSaeS/R sensory system to sense and adapt to neutrophil challenge. Experiments outlined in Specific Aim 1will use host-pathogen NGS RNA-seq to identify human neutrophil components influenced by SaeR/S, novelSaeR/S regulated virulence factors induced upon neutrophil exposure, as well as resolve the influence ofindividual components of the sae system (saeP, saeQ, saeR, and saeS) on virulence regulation. Preliminarydata demonstrates our ability to successfully perform these technically challenging experiments. Specific Aim 2of this proposal will test an innovative hypothesis that a newly identified SaeR/S-dependent virulence factorinhibits neutrophil reactive oxygen species, independent of previously defined mechanisms, via targetinghuman myeloperoxidase. Experiments outlined in Specific Aim 3 will explore unique findings that indicateSaeR/S-regulated factors manipulate IFN? and IL-17A production during skin and soft-tissue infection, drivinghost immunity towards a TH1-type immune response associated with increased pathogenesis and away from aprotective Th17-type response. Collectively, this study will advance understanding of sense-and-responseadaptations by S. aureus to improve our knowledge of the initial host-pathogen interactions that lead to S.aureus infection. Results will provide valuable information for vaccine and immunotherapeutic development.