Project Summary Staphylococcus aureus (Sa) is a leading cause of nosocomial infection in the United States and is a predominant pathogen in communities. Treatment of Sa infections is complicated by the prevalence of antibiotic resistant and highly virulent clones, making new therapeutic alternatives a necessity. Sa survives during infection by subverting immune defenses and adapting to host-imposed nutrient restriction. Yet, we lack a unifying understanding of these adaptations to the host environment, which complicates the development of new therapeutics and vaccines. We recently discovered that a cofactor required for metabolic enzyme complex function and potent antioxidant, lipoic acid (LA), is a critical mediator of Sa growth and survival during infection. Furthermore, we found that Sa releases the lipoylated E2 subunit of the metabolic enzyme complex pyruvate dehydrogenase to blunt protective innate immune responses via its LA moiety. Thus, our work has uncovered a mechanism of Sa survival during infection that links bacterial metabolism and nutrient acquisition to defense against innate immunity. Despite establishing these roles for LA biosynthesis and salvage in Sa pathobiology, there exist major gaps in our understanding of the mechanics of how LA blunts immunity and promotes optimal metabolism during infection. Notably: (i) the precise mechanism by which bacterial LA-protein blunts immune activation has not been elucidated; (ii) regulation of LA distribution on essential metabolic enzymes is not understood; (iii) the role of LA in mediating defense against oxidative stress has not been investigated; and (iv) the relevance of LA acquisition to survival in different infection sites is not understood. This renewal application will address these gaps in knowledge by ascertaining precisely how LA subverts immunity and the mechanics of LA synthesis/salvage that promote bacterial survival in vivo with the potential to lay the groundwork for new targeted therapeutics. Aim 1 will determine how bacterial-derived LA blunts immune responses. Aim 2 will determine how Sa regulates LA salvage and distribution. Aim 3 will investigate how accessibility to host nutrients in different tissues determines the requirement for LA during infection.