Urease promotes pH homeostasis and growth of Staphylococcus aureus in skin-like conditions

Staphylococcus aureus is a Gram-positive opportunistic pathogen and a leading cause of skin and soft tissue infections (SSTIs). S. aureus colonizes approximately 20-30% of the population and transiently colonizes the skin. Although skin colonization is an SSTI risk factor, our understanding of S. aureus requirements to persist in this environment is still developing. The human skin is acidic, with a ubiquitous distribution of eccrine glands, which secrete metabolites, such as urea onto the skin surface. Many pathogens break down urea into ammonia and carbon dioxide by the Ni(II)-dependent enzyme urease as an acid resistance mechanism. S. aureus relies on urea metabolism for pH homeostasis in the murine kidney, but a role for this process on skin has not been shown. Using an in vitro model of the human skin surface environment, we investigated the role of urease in the methicillin-resistant USA300 strain S. aureus subsp. aureus (MRSA) LAC. We observe that urease contributes to an increase in extracellular pH and production of extracellular ammonium, which results in ammonium becoming a shared good in a mixed culture. We also demonstrate that the putative urea transporter SAUSA300_2237 (ureT) is required for optimal extracellular ammonia generation. Finally, we show that the urease inhibitor fluorofamide effectively inhibits S. aureus urease activity. This work identifies a role for urea metabolism during S. aureus skin colonization and offers the first published characterization of the S. aureus putative urea transporter, UreT.IMPORTANCEThe human skin is a unique microbial environment that has been challenging to faithfully model in the laboratory. Here, we utilize a recently developed media recipe incorporating metabolites measured from healthy human skin to assess the role of urease in Staphylococcus aureus pH homeostasis in the skin environment. These data provide new insights into the role of urea metabolism in S. aureus pH homeostasis during skin colonization. We also describe the first characterization of transporter SAUSA300_2237 (ureT) and demonstrate its role in urea metabolism. These insights advance our understanding of this metabolic pathway in S. aureus.