The biofilm mode of growth has been implicated in the majority of human bacterial infections. In the urinary tract, notable biofilm-associated infections include prostatitis, chronic cystitis, struvite urolithiasis, and catheter-associated infections. Biofilms protect the causative organisms from host defences and antimicrobial therapy. Biofilm formation has traditionally been considered to result from adhesion and capsule formation by adherent microorganisms. Recent work has shown that a large number of genes are activated during this process, some of which have been associated with twitching motility, quorum sensing, and slow growth. In this paper, we review some of the recent work on biofilm biology and highlight its role in urinary tract infections, particularly those associated with urinary catheters.

Objective  To test the resistance of currently available types of indwelling urethral catheters to blockage by encrustation with mineralized Proteus mirabilis biofilms. Materials and methods  Encrustation was studied in a simple laboratory model of the catheterized bladder. Artificial urine was supplied to the bladder chamber at 0.5 mL/min. The bladder urine was inoculated with a clinical strain of P. mirabilis that had been isolated from an encrusted catheter. The models were operated until the catheters blocked and atomic absorption spectrometry was used to assess the amounts of calcium and magnesium deposited on the catheters. Scanning electron microscopy was also used to locate and assess the degree of encrustation. Results  The mean times to blockage ranged from 21 h for the Bard hydrogel/silver‐coated latex catheter to 56 h for the Eschmann Folatex S all‐silicone catheter. The calcium and magnesium salts were mainly deposited on the 10 cm below the eye‐holes of the catheters, complete blockage generally occurring in the 2 cm immediately below the eye‐hole. Conclusion  None of the 18 types of catheter tested, including those coated with hydrogel or silver, were capable of resisting encrustation by P. mirabilis biofilm.

No abstract

No abstract

Acylated homoserine lactones (AHLs) are chemical signals that mediate population density-dependent (quorum-sensing) gene expression in numerous gram-negative bacteria. In this study, gram-negative bacilli isolated from catheters were screened for AHL production by a cross-feeding assay utilizing an AHL-responsive Agrobacterium tumefaciens reporter strain. Positive reactions were obtained from 14 isolates of Pseudomonas aeruginosa; negative or weakly positive reactions were recorded for isolates of five other species. P. aeruginosa biofilms were then produced on catheters in a physical model of the bladder. Sections of colonized all-silicone catheters gave positive reactions for the quorum-sensing signal molecules as did sections that had been cleaned of biofilm and autoclaved. Control sections of unused catheters were negative in the tests. Sections from four of nine catheters that had been freshly removed from patients gave positive reactions for AHLs. Cleaned autoclaved sections of three of these catheters also gave strongly positive reactions for AHLs. These results demonstrate that AHLs are produced by biofilms as they develop on the catheters both in vitro in the model and in vivo in the patient’s bladder. They represent the first demonstration of AHL production by biofilms in a clinical setting.

Encrustation and blockage of indwelling urethral catheters is primarily brought about by infection of the urinary tract by Proteus mirabilis or other urease-producing species. The bacteria colonise the catheter forming a biofilm community within a polysaccharide matrix. The activity of the urease drives up the urinary pH and causes the crystallisation of calcium and magnesium phosphates in the biofilm. We have used a simple physical model of the catheterised bladder to investigate the ability of urease inhibitors to control encrustation. It was observed that acetohydroxamic acid (1.0 mg/ml) and fluorofamide (1.0 microg/ml) restricted the increase in pH of P. mirabilis-infected urine from 9.1 to 7.6. Significant reductions in the deposition of calcium and magnesium salts were also recorded on the silicone catheters. Electron microscopy confirmed that encrustation and occlusion of the catheter lumen was minimal in the presence of the urease inhibitors. The data from this in vitro study suggests that urease inhibitors, particularly fluorofamide, could have clinical applications in the prevention of catheter encrustation and blockage.

A model of the catheterised bladder was used to test the ability of urease-producing urinary tract pathogens to encrust urethral catheters. Encrustation was assessed by determining the amounts of calcium and magnesium deposited on the catheters and visualised by scanning electron microscopy. Urease-positive Morganella morganii, Klebsiella pneumoniae, and Pseudomonas aeruginosa failed to raise the urinary pH and form crystalline biofilms. In contrast, strains of Proteus mirabilis, Proteus vulgaris, and Providencia rettgeri generated alkaline urine (pH 8.3-8.6) and extensive catheter encrustation within 24 h.

Aims:  Infection of the catheterized urinary tract with Proteus mirabilis causes blockage of the catheter by crystalline bacterial biofilms. The aim of this work is to identify a surface‐coating for catheters that is not vulnerable to colonization by Pr. mirabilis. Methods and Results:  A parallel‐plate flow‐cell and phase contrast microscopy were used to follow bacterial adhesion onto polymer films. Experiments with a urease‐negative mutant of Pr. mirabilis suspended in buffer or urine, identified agarose as a polymer on which biofilm did not form. In tests with wild‐type urease‐producing cells in urine, no adhesion of cells onto agarose was observed for 3 h but then as the pH rose above 8·2, the surface rapidly became colonized by crystalline biofilm. Conclusions:  In urine at pH below 8·0, Pr. mirabilis does not adhere to agarose‐coated surfaces. When the pH rises above 8·2, however, aggregates of crystals and bacteria form in the urine and are deposited on such surfaces. Significance and Impact of the Study:  Strategies to prevent the formation of crystalline biofilms on urinary catheters will need to consider both the properties of the surface‐coatings and the requirement to prevent the alkaline conditions that induce crystal formation in urine.