Metabolic interplay between Proteus mirabilis and Enterococcus faecalis facilitates polymicrobial biofilm formation and invasive disease.

Catheter-associated urinary tract infections (CAUTI) account for 40% of all nosocomial infections and can lead to significant life-threatening complications such as bacteremia. Microbial biofilms play an important role in the development and pathogenesis of CAUTI, and these biofilms are often polymicrobial. Proteus mirabilis and Enterococcus faecalis are two of the most common causes of CAUTI, and they often persistently co-colonize the catheterized urinary tract. We previously demonstrated that co-culture of E. faecalis with P. mirabilis increased biofilm biomass, antimicrobial resistance, and disease severity. In this study, we uncover the metabolic interplay that drives biofilm enhancement and examine the contribution of this polymicrobial interaction to CAUTI severity. Though compositional and proteomic biofilm analyses, we determined that the increase in biofilm biomass stems from an increase in the protein fraction of the polymicrobial biofilm. We further observed an enrichment in proteins associated with ornithine and arginine metabolism in polymicrobial biofilms compared to single- species biofilms. By testing mutants of E. faecalis and P. mirabilis, we found that L-ornithine secreted by the E. faecalis ArcD antiporter promotes L-arginine biosynthesis in P. mirabilis via ArgF, which ultimately fuels production of proteins that facilitate contact-dependent interactions to enhance biofilm biomass. We further demonstrate that ArcD and ArgF are not important for urinary tract colonization by either species when alone, but ornithine/arginine interplay is critical for the increased disease severity that occurs during coinfection. This study provides deeper insight into the polymicrobial interactions occurring during CAUTI and highlights how these interactions can have significant impacts on pathogenesis and bacterial persistence.