Staphylococcus aureusis a significant cause of chronic biofilm infections on medical implants. We investigated the biofilm regulatory cascade and discovered that the repressor of toxins (Rot) is part of this pathway. A USA300 community-associated methicillin-resistantS. aureusstrain deficient in Rot was unable to form a biofilm using multiple different assays, and we foundrotmutants in other strain lineages were also biofilm deficient. By performing a global analysis of transcripts and protein production controlled by Rot, we observed that all the secreted protease genes were up-regulated in arotmutant, and we hypothesized that this regulation could be responsible for the biofilm phenotype. To investigate this question, we determined that Rot bound to the protease promoters, and we observed that activity levels of these enzymes, in particular the cysteine proteases, were increased in arotmutant. By inactivating these proteases, biofilm capacity was restored to the mutant, demonstrating they are responsible for the biofilm negative phenotype. Finally, we tested therotmutant in a mouse catheter model of biofilm infection and observed a significant reduction in biofilm burden. ThusS. aureususes the transcription factor Rot to repress secreted protease levels in order to build a biofilm.
Staphylococcus aureus is a significant cause of chronic biofilm infections and the repressor of toxins (Rot) controls this pathogenesis mechanism. When Rot is removed, the level of secreted cysteine protease activity increases, resulting in a decrease in the S. aureus capacity to form a biofilm and reduced bacterial burden in a mouse catheter model of biofilm infection.