NUTRITIONAL REGULATION OF PATHOGENESIS IN STAPHYLOCOCCUS AUREUS

7. Project Summary/AbstractStaphylococcus aureus is the leading cause of life threatening skin and soft tissue infections, osteomyelitis,pneumonia and endocarditis, but spends much of its time as a commensal bacterium, colonizing 30-50% of thepopulation asymptomatically. Vaccine candidates show promise for highly susceptible populations, but ageneral, effective approach to preventing staphylococcal infections remains elusive. Moreover, the mechanisticbasis for the commensal-to-pathogen switch is complex and remains unsolved, but changing nutrientavailability in the various environments of the human host likely plays an important role in informing thebacterium's decision to switch between lifestyles. The global transcriptional regulator CodY is activated byisoleucine, leucine, valine (ILV) and GTP, and adjusts metabolism and virulence gene expression. Ourpreliminary data indicate that CodY activity is not binary (i.e., on or off). Rather, CodY can sense a range ofconcentrations of ILV and GTP to generate a hierarchical transcriptional and physiological response. That is,under conditions of increasing ILV and GTP depletion, toxins and spreading factors are sequentially induced.Additional work by our lab has shown that CodY controls nearly all of the known virulence genes in conjunctionwith three of the most important regulators of S. aureus virulence: the Sae two-component system, theregulatory protein Rot, and the Agr quorum-sensing system. In collaboration with staphylococcal biologistsChristopher Montgomery (Nationwide Children's Hospital), Victor Torres (NYU School of Medicine), and TaeokBae (Indiana School of Medicine-NW), we will unravel the mechanistic basis by which CodY ties virulence tonutrient availability. We will use LC-MS based metabolomics, confocal microscopy, classical moleculargenetics and biochemistry to (i) determine the mechanisms by which CodY regulates the expression of the saelocus, and (ii) determine how nutrient availability alters the activity of the Sae Two Component System.Additionally, we will explore mechanistically how CodY constrains virulence during S. aureus-immune cellencounters as well as during skin and soft tissue infection using a mouse model of S. aureus dermonecrosis.Understanding how nutrient signals are integrated into the virulence regulatory network by factors like CodYcan potentially inform the rational design of novel antimicrobials that limit host damage, desperately replacingobsolete antibiotics in an era of pan-resistance.