Supplementary Material for: The Role of Innate Immunity in Promoting SaeR/S-Mediated Virulence in Staphylococcus aureus

The ability of <i>Staphylococcus aureus</i> to infect tissues is dependent on precise control of virulence through gene-regulatory systems. While the SaeR/S two-component system has been shown to be a major regulator of <i>S. aureus</i> virulence, the influence of the host environment on SaeR/S-regulated genes (<i>saeR/S </i>targets) remains incompletely defined. Using QuantiGene 2.0 transcriptional assays, we examined expression of genes with the SaeR binding site in USA300 exposed to human and mouse neutrophils and host-derived peptides and during subcutaneous skin infection. We found that only some of the <i>saeR/S </i>targets, as opposed to the entire SaeR/S virulon, were activated within 5 and 10 min of interacting with human neutrophils as well as α-defensin. Furthermore, mouse neutrophils promoted transcription of <i>saeR/S</i> targets despite lacking α-defensin, and the murine skin environment elicited a distinctive expression profile of <i>saeR/S</i> targets. These findings indicate that <i>saeR/S</i>-mediated transcription is unique to and dependent on specific host stimuli. By using isogenic USA300Δ<i>saeR/S</i> and USA300Δ<i>agr</i> knockout strains, we also determined that SaeR/S is the major regulator of virulence factors, while Agr, a quorum-sensing two-component system, has moderate influence on transcription of the <i>saeR/S </i>targets under the tested physiological conditions.