Encrustation of indwelling urethral catheters by Proteus mirabilis biofilms growing in human urine.

The encrustation and blockage of four types of urinary catheters was studied in a simple laboratory model of the catheterized bladder. Pooled human urine was supplied to the bladder chamber at 0.5 mL/min. The bladder urine was inoculated with a clinical strain of Proteus 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. All catheters blocked rapidly, the mean times to blockage ranging from 17.7 h (silver-coated latex), 34 h (hydrogel-coated latex), 38 h (silicone-coated latex) to 47 h (all silicone). The internal diameters of the latex catheters were only 1.5 mm compared to the 2.5 mm of the all-silicone catheters. The calcium and magnesium salts were deposited on the lumenal surfaces along the full length of catheters but occurred most extensively just below the eye-holes. There is clearly a need to develop catheter surfaces which resist encrustation by crystalline biofilms of P. mirabilis.