Staphylococcus aureus urease is controlled by a complex regulatory network and promotes dissemination during catheter-associated urinary tract infections (CAUTI)

Abstract

Catheter-associated urinary tract infections (CAUTIs) are one of the most common hospital-associated infections in the United States, accounting for >1 million cases annually. One CAUTI-associated pathogen, Staphylococcus aureus, is commonly found persisting asymptomatically in the bladder of catheterized individuals, increasing these individuals risk of developing CAUTI. Importantly, S. aureus is not only associated with severe symptoms, including bacteremia and septic shock, but it also produces a common uropathogen associated virulence factor, urease. Despite its importance, urease has only been well-studied in the uropathogen Proteus mirabilis. While previous studies identified three S. aureus urease regulators, CodY, CcpA, and Agr, the environmental signals required for expression and activity, and the contribution of urease to CAUTI have not been explored. In this study, we investigate how the urease regulatory pathways coordinate expression and activity in response to environmental signals present within the catheterized urinary tract. Our findings demonstrate that stationary phase significantly induces S. aureus urease expression and activity. Additionally, we identified predicted binding sites in the urease promoter for three regulators previously implicated in urease expression - CodY, CcpA, and SigB - as well as SrrA - a previously unrecognized regulator of urease. A binding site for Agr was not present in the urease promoter. Expression and activity assays confirm the role of CodY, CcpA, SigB, SrrA, and Agr in regulating urease. Importantly, single nucleotide polymorphisms identified in the urease promoter of clinical isolates enhance urease expression. Additionally, urease promotes biofilm formation under catheterized urinary tract-like conditions in vitro and dissemination from the bladder to the kidneys at 1 day post infection in a mouse CAUTI model. Together, our data not only provide insight into the regulatory pathway controlling S. aureus urease but also emphasize the importance of studying these mechanisms in a model that mimics the host environment. AUTHOR SUMMARYCatheter-associated urinary tract infections (CAUTIs) are common hospital-associated infections and are caused by many different pathogens. Of these pathogens, Staphylococcus aureus is particularly problematic, as it often spreads to the bloodstream and results in septic shock. One of the primary virulence factors that is important for uropathogens is urease. Urease breaks down urea in urine, which results in crystalline structures that encrust urinary catheters and promote reflux to the kidney. Despite producing urease, little is known about how S. aureus regulates the enzyme. In this study, we investigate how regulatory pathways coordinate the expression and activity of urease in response to environmental signals. We show that growth during stationary phase and in conditions that mimic the urinary tract urease expression and activity are increased. We also show that five different regulators - CodY, CcpA, SigB, SrrA, and Agr control urease expression and activity. Additionally, genomic changes identified in the urease regulatory pathway of clinical urinary catheter-associated isolates enhance urease expression. Importantly, urease promotes biofilm formation and dissemination during CAUTI. Our study provides insight into the complex regulatory mechanisms controlling urease and highlights the role urease plays in the development and virulence of S. aureus CAUTI.