Global changes in Staphylococcus aureus virulence and metabolism during colonization of healthy skin

Staphylococcus aureus and its antibiotic-resistant derivative, methicillinresistant S. aureus (MRSA), are the leading causative agents of skin and soft tissue infections globally. S. aureus transiently colonizes the skin of healthy adults, and this transient colonization likely precedes an active infection. In recent years, there have been efforts to elucidate specific factors that help MRSA transition to an active infec tion, but the specific genetic determinants required for this transition following skin colonization are largely unknown. To address this question, we developed a model of asymptomatic colonization of mouse skin by MRSA. From this model, we could determine the MRSA and mouse transcriptional profiles by RNA sequencing (RNAseq) at 5- and 24-hour post-colonization. The fadXDEBA locus, required for fatty acid metabo lism, was highly upregulated in our data, as were numerous virulence factors. RNAseq data were confirmed via functional in vitro and in vivo promoter-fusion assays using live bioluminescent imaging of the fadXDEBA locus promoter driving fadB transcription. We analyzed the functional capacity of members of the fadXDEBA locus, which encode crucial enzymatic components of the S. aureus beta-oxidation pathway. The genes fadD and fadA modulate MRSA resistance to fosfomycin and other oxidative stressors during growth in the presence of the common skin fatty acid, palmitic acid. Overall, our data demonstrate that there are global changes to the MRSA transcriptome, priming the bacteria for survival by upregulation of known virulence factors and metabolic genes implicated in host skin-nutrient utilization.