Introduction: Catheter-associated UTIs (CA-UTIs) account for 80% of all hospital-acquired UTIs. Proteus mirabilis causes ~44% of all CA-UTIs. P. mirabilis oversecretes the virulence factor urease to alkylate urine and enhance survival. Alkylation precipitates calcium and magnesium to form crystalline biofilms that block indwelling catheters, causing a backflow of urine and consequently, pyelonephritis and septicaemia.
Acetohydroxamic acid, the only approved urease inhibitor, has severe side effects. Furthermore, antibiotic therapy alone does not prevent biofilm formation or catheter encrustation, thus necessitating better alternatives. Here we investigated the biofilm disrupting agent N-acetylcysteine (NAC) in preventing catheter encrustation.
Methods: Urease activity from five clinical P. mirabilis isolates treated for 2hrs with a range of NAC concentrations were quantified using Berthelot’s method. Enzyme kinetics were studied using purified commercial urease with urea degradation quantified by spectrometry.
Silicone catheter encrustation was investigated in the presence of NAC using an in vitro glass bladder model, where a 2-way Foley catheter was “infected” with P. mirabilis. Artificial urine with NAC was pumped through the catheter and the “infection” process allowed to run for 120hrs or complete blockage. Inductively coupled plasma mass spectrometry analysis was used on catheter eye sections with differences in elemental profiles of deposits in catheters compared.
Results: NAC suppressed P. mirabilis urease activity by >3-fold in concentrations >5mM and exhibited competitive inhibition of urease in vitro. Kinetics studies showed strong binding capacity of NAC to urease. NAC significantly delayed complete blockage of catheters to >96hrs, compared to untreated catheters, and significantly decreased bacterial loads (>3 log10 CFU/mL) in catheter cross-sections. NAC also resulted in a significant >4-fold decrease in biofilm bacteria.
Conclusion: NAC is a non-toxic agent with potent urease inhibitory effect that is mutually exclusive from its bactericidal properties. Inhibiting urease activity effectively disarms P. mirabilis- the primary cause of catheter blockage and biofilm formation. With dual inhibitory capacities, NAC allows CAUTI treatment in a highly targeted and efficient manner without promoting antibiotic resistance.