Limiting Protease Production Plays a Key Role in the Pathogenesis of the Divergent Clinical Isolates of LAC and UAMS-1

Using the USA300, methicillin-resistant strain LAC, we previously examined the impact of regulatory mutations implicated in biofilm formation on protease production and virulence in a murine sepsis model. Here we examined the impact of these mutations in the USA200, methicillin-sensitive strain UAMS-1. Mutation of and attenuated the virulence of UAMS-1. A common characteristic of , and mutants was increased protease production, with mutation of having the least impact followed by mutation of and , respectively. Protein A was undetectable in conditioned medium from all four mutants, while extracellular nuclease was only present in the proteolytically cleaved NucA form. The abundance of high molecular weight proteins was reduced in all four mutants. Biofilm formation was reduced in and mutants, but not in the mutant. Eliminating protease production partially reversed these phenotypes and enhanced biofilm formation. This was also true in LAC and mutants. Eliminating protease production enhanced the virulence of LAC and UAMS-1 and mutants in a murine sepsis model but did not significantly impact the virulence of the mutant in either strain. Nevertheless, these results demonstrate that repressing protease production plays an important role in defining critical phenotypes in diverse clinical isolates of and that Rot, SigB and SarA play critical roles in this regard.