Staphylococcus aureus (S. aureus) is one of the most frequent causes of bacterial infections in the U.S. and is
responsible for diverse types of infections ranging in severity from mild to fatal in both hospital and community
settings. 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 necrotizing
fasciitis 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 develop
resistance to antibiotics making it very difficult to develop therapeutics that will have potential for long-term
efficacy 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 novel
vaccines and therapies to treat bacterial infection. Research that defines protective host immune responses
and the mechanisms used by pathogens to undermine them can be translated to new treatment strategies that
will improve public health. Based on strong published and preliminary findings using mouse models of
infection and human neutrophil assays, we have identified specific host and pathogen factors that will be
investigated to determine their precise roles in pathogenesis. To that end, this project will study how S. aureus
uses the SaeR/S two-component gene regulatory system to evade innate immunity. The SaeR/S system is
essential for evasion of neutrophil killing; however, exact mechanisms dependent on SaeR/S resulting in
neutrophil dysfunction are not defined. Three specific aims will test the hypothesis that S. aureus uses the
SaeS/R sensory system to sense and adapt to neutrophil challenge. Experiments outlined in Specific Aim 1
will use host-pathogen NGS RNA-seq to identify human neutrophil components influenced by SaeR/S, novel
SaeR/S regulated virulence factors induced upon neutrophil exposure, as well as resolve the influence of
individual components of the sae system (saeP, saeQ, saeR, and saeS) on virulence regulation. Preliminary
data demonstrates our ability to successfully perform these technically challenging experiments. Specific Aim 2
of this proposal will test an innovative hypothesis that a newly identified SaeR/S-dependent virulence factor
inhibits neutrophil reactive oxygen species, independent of previously defined mechanisms, via targeting
human myeloperoxidase. Experiments outlined in Specific Aim 3 will explore unique findings that indicate
SaeR/S-regulated factors manipulate IFN¿ and IL-17A production during skin and soft-tissue infection, driving
host immunity towards a TH1-type immune response associated with increased pathogenesis and away from a
protective Th17-type response. Collectively, this study will advance understanding of sense-and-response
adaptations 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.
