Functional\nand Proteomic Dissection of the Contributions\nof CodY, SigB and the Hibernation Promoting Factor HPF to Interactions\nof <i>Staphylococcus aureus</i> USA300 with Human Lung Epithelial\nCells

<i>Staphylococcus aureus</i> is a leading cause\nof severe\npneumonia. Our recent proteomic investigations into <i>S. aureus</i> invasion of human lung epithelial cells revealed three key adaptive\nresponses: activation of the SigB and CodY regulons and upregulation\nof the hibernation-promoting factor SaHPF. Therefore, our present\nstudy aimed at a functional and proteomic dissection of the contributions\nof CodY, SigB and SaHPF to host invasion using transposon mutants\nof the methicillin-resistant <i>S. aureus</i> USA300. Interestingly,\ndisruption of <i>codY</i> resulted in a “small colony\nvariant” phenotype and redirected the bacteria from (phago)lysosomes\ninto the host cell cytoplasm. Furthermore, we show that CodY, SigB\nand SaHPF contribute differentially to host cell adhesion, invasion,\nintracellular survival and cytotoxicity. CodY- or SigB-deficient bacteria\nexperienced faster intracellular clearance than the parental strain,\nunderscoring the importance of these regulators for intracellular\npersistence. We also show an unprecedented role of SaHPF in host cell\nadhesion and invasion. Proteomic analysis of the different mutants\nfocuses attention on the CodY-perceived metabolic state of the bacteria\nand the SigB-perceived environmental cues in bacterial decision-making\nprior and during infection. Additionally, it underscores the impact\nof the nutritional status and bacterial stress on the initiation and\nprogression of staphylococcal lung infections.