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.

金黄色葡萄球菌（Staphylococcus aureus）感染宿主组织的能力，依赖于通过基因调控系统对毒力进行精准调控。已有研究证实，SaeR/S双组分系统（SaeR/S two-component system）是金黄色葡萄球菌毒力的主要调控因子，但宿主环境对SaeR/S调控基因（即saeR/S靶基因）的影响仍未完全明确。本研究采用QuantiGene 2.0转录检测试剂盒（QuantiGene 2.0 transcriptional assays），针对暴露于人源、鼠源中性粒细胞及宿主来源肽的USA300菌株，以及皮下皮肤感染模型中的USA300菌株中携带SaeR结合位点的基因表达水平进行了检测。研究结果显示，与完整的SaeR/S毒力因子组（virulon）不同，仅部分saeR/S靶基因在与人类中性粒细胞及α-防御素（α-defensin）相互作用后的5分钟和10分钟内被激活。此外，尽管鼠源中性粒细胞不表达α-防御素，但仍可促进saeR/S靶基因的转录；而小鼠皮肤微环境则可诱导saeR/S靶基因呈现独特的表达谱。上述发现表明，saeR/S介导的转录具有宿主特异性，且依赖于特定的宿主刺激信号。本研究还通过构建同基因背景的USA300ΔsaeR/S与USA300Δagr敲除菌株，明确了在本次检测的生理条件下，SaeR/S是毒力因子的主要调控因子，而群体感应双组分系统（quorum-sensing two-component system）Agr则对saeR/S靶基因的转录仅具有中等程度的调控作用。