Global usage of urinary catheters exceeds 100 million devices annually; ~50% of patients with long term indwelling catheters experience catheter blockage, which often require Emergency Department care. Bacterial biofilms are the primary cause of catheter blockage, predominantly from two species. Proteus mirabilis biofilms are crystalline (struvite) whereas Pseudomonas aeruginosa biofilms have a sticky mucoid phenotype. Antibiotics are ineffective.  To resolve catheter blockage, an effective formulation must remove the biofilm. 

A validated glass bladder model replicated the catheterised bladder in vitro, demonstrating fresh liquid N-acetylcysteine (NAC) inhibits P mirabalis and P aeruginosa biofilms and prevents bladder cell invasion by uropathogens [1-3]. Acidic conditions are important to biofilm removal, as are bacteriostats, chelating agents and tonicity. Testing has established NAC must be used in combination as it is not stable in liquid form. Here we investigated a combination of tests to demonstrate the multi-factorial variables important for catheter biofilm disruption, yielding novel results.

Two candidate formulations (termed 40-3 & 40-4), which comprised an acid (pH4), a brominated bacteriostat, and a chelating agent were investigated without NAC (40-4 is differentiated by the addition of normal saline which increases tonicity). 

Blocked/encrusted indwelling patient catheters collected from a metropolitan Continence Unit, were cross sectioned and biofilm encrustations harvested. Bacterial species were identified via routine MALDI-TOF. 

A struvite dissolution assay was established and treated with 1mL of test formulations, incubated (37°C/10min) and qualitatively assessed.

The glass bladder model tested P mirabalis crystalline biofilm disruption factors in urinary catheters (Fig1 A,B). 40-4 was pumped through the catheter and held by clamping (30mins). Catheters were sampled at the eye, 3cm and 5cm below the eye (Fig 1C).

Both P mirabilis and P aeruginosa biofilms were established in a multi-well plate method. Commercially available catheter clearance solutions containing citric acid (CA) (3.2% & 6%) & PHMB (0.02%) were assessed against both 40-3 & 40-4 solutions (Fig2). 

Formulation cytotoxicity was tested per ISO10993 using bladder epithelial cells.

Dominant species in blocked patient catheters were P mirabilis, P aeruginosa and E coli.  >50% of catheters showed dual species biofilms, with P. aeruginosa as one of the infecting organisms. Biofilm encrustations were heterogeneous along the catheter length.

Both 40-3 & 40-4 completely dissolved struvite. Commercially available CA solutions had comparable struvite dissolution efficacy, whereas PHMB showed no dissolution.

P. mirabilis catheter biofilms were significantly disrupted by 40-4 in the glass bladder model, reducing viable bacteria by 4 Log10 CFU/mL across all catheter sections versus control (Fig 1C). 

40-3 significantly disrupted P aeruginosa and P mirabilis biofilms (p<0.0001) (Fig2). 40-4 also significantly disrupted P mirabilis biofilms (p<0.0001) and to a lesser extent P aeruginosa biofilms (p<0.001) suggesting tonicity is an important, unrecognised feature in mucoid biofilm removal.  Commercially available 6.0% CA and PHMB were less effective than 40-3 and 40-4, and 3.2% CA was ineffective against P. aeruginosa biofilms (Fig 2B). 

Both 40-3 and 40-4 were found to be bacteriostatic when tested against planktonic P aeruginosa and P mirabalis. Both 40-3 & 40-4 passed cytotoxicity limits as per ISO10993.

The cause of catheter blockages are complex biofilms. These require a multi-factorial approach including acidity, tonicity and bacteriostatic performance to disrupt both crystalline and mucoid catheter biofilms. Our results demonstrate a highly statistically significant improvement (p<0.0001) for 40-3 over the current commercial solutions. Investigations are continuing with patient catheters and a novel intracellular bacterial biofilm assay to include NAC with other key excipients.

These experimental results spotlight the need to improve approaches to biofilm disruption in blocked catheters, to alleviate patient morbidity.

Manoharan et al. Biofilm. 2025 Jun 25;10:100296. doi: 10.1016/j.bioflm.2025.100296. PMID: 40726828.
Manoharan et al. Front Cell Infect Microbiol. 2023 Oct 26;13:1216798. doi: 10.3389/fcimb.2023.1216798. PMID: 37965267.
Manoharan et al. Antibiotics (Basel). 2021 Jul 23;10(8):900. doi: 10.3390/antibiotics10080900. PMID: 34438950.

Continence 19S (2026) 102668
DOI: 10.1016/j.cont.2026.102668