Background: P. aeruginosa accounts for 20% of all nosocomial UTIs, often associated with biofilm encrustation of indwelling catheters. Previous studies windicate that urine influences downregulation of quorum sensing (QS), potentially increasing susceptibility to clearance by host immune system. Despite this, P. aeruginosa has adapted to thrive and establish biofilms in the urinary tract environment. In this study, we investigated the effect of urine on the P. aeruginosa biofilm matrix composition and its immunogenicity against uroepithelial cells.
Methods: Biofilm matrices of uropathogenic P. aeruginosa biofilms grown in synthetic urine in catheter cross sections were harvested using a series of gradient and chemical centrifugation steps. Protein, eDNA, polysaccharides and pyocyanin were quantified using standard methods. To study the effect of the biofilm matrix on urothelial cellular inflammation, uroepithelial cell monolayers (ATCC 5637) were treated with different fractions of the harvested biofilm matrix without bacteria for 6, 12 and 24hrs. Pro-inflammatory cytokines and rates of wound healing were quantified.
Results: Urine grown biofilm matrices, showed a >3-fold increase in protein concentrations, and a significant reduction in polysaccharides (p<0.01), compared to nutrient broth controls. The protein fraction elicited the strongest inflammatory response from urothelial cells, with a significant increase in IL-6, IL-8 and IL-1b in response to infection (>2-4 fold compared to untreated controls, p<0.05) and a significant reduction in rate of wound healing in vitro. No significant differences were recorded between the polysaccharide and eDNA fractions.
Conclusion: Urine significantly influences the composition and immunogenicity of the P. aeruginosa biofilm matrix. Urine biofilms have a larger protein fraction compared to controls. The matrix is highly immunogenic to uroepithelial cells, indicating that its role in UTIs extends beyond bacterial protective mechanisms. This work highlights the importance of optimizing treatment options to target the biofilm matrix and tackle catheter infections.