Biofilms play a therapeutically defining role in many forms of Staphylococcus aureus infection including endocarditis, osteomyelitis, and infections associated with indwelling medical devices including orthpaedic implants. This is because the biofilm confers a therapeutically relevant level of intrinsic resistance to both host defenses and conventional antimicrobial agents. This means that the treatment of such infections most often requires surgical intervention to remove infected tissues and/or infected indwelling devices, and this is true even when the infection is caused by a bacterial strain that is fully sensitive to the antibiotic of choice. The ability of S. aureus to cause biofilm-associated infection is defined by ts ability to accomplish two tasks, the first being to persist in the bloodstream to an extent that promotes the colonization of extravascular sites and implanted devices, and the second being the ability to effectively colonize these sites and ultimately gain the intrinsic safety of a bioilm. The underlying hypothesis behind this proposal is that the ability of S. aureus to accomplish both of these tasks is dependent on the staphylococcal accessory regulator (sarA). The experimental hypothesis is that sarA must simultaneously promote the production of key virulence factors and repress the production of extracellular proteases that would otherwise limit, if not reverse, the phenotypic impact of these virulence factors. This hypothesis is based on our demonstration that mutation of sarA attenuates the virulence of S. aureus in murine models of both bacteremia and biofilm-associated infection. In the context of the first of these models, this attenuation can be correlated with a reduced capacity to cause secondary, biofilm-associated infections, while in the context of the second it can be correlated with increased antibiotic susceptibility and an improved therapeutic outcome. In addition, eliminating the ability of sarA mutants to produce extracellular proteases largely reverses this attenuation in both models. Thus, we have uncovered a key mechanistic component that we can exploit to our experimental advantage to identify key virulence factors that contribute to these important, sarA-dependent phenotypes. This will in turn provide the mechanistic basis required for the development of novel therapeutic strategies that can be used to overcome the growing problem of S. aureus biofilm associated infections.