OBJECTIVE: To test the recommendation that to avoid the complications of long-term indwelling bladder catheterization (e.g. encrustation and blockage by crystalline Proteus mirabilis biofilms) patients should drink cranberry juice.

MATERIALS AND METHODS: Urine was collected from groups of volunteers who had drunk up to 2 x 500 mL of cranberry juice or water within an 8-h period. Laboratory models of the catheterized bladder were supplied with urine from these groups and inoculated with P. mirabilis. After incubation for 24 or 48 h, the extent of catheter encrustation was determined by chemical analysis for calcium and magnesium. Encrustation was also visualized by scanning electron microscopy.

RESULTS: The amounts of calcium and magnesium recovered from catheters incubated in urine pooled from individuals who had drunk 500 mL of cranberry juice was not significantly different from that on catheters incubated in pooled urine from control subjects who had drunk 500 mL of water. However, there was significantly less encrustation (P = 0.007) on catheters from models receiving urine from volunteers who had drunk 2 x 500 mL of water than on catheters incubated in models supplied with urine from volunteers who had drunk 2 x 500 mL of cranberry juice. The amounts of encrustation on these two groups of catheters were also significantly less than that on catheters incubated in models supplied with urine from volunteers who had not supplemented their normal fluid intake. (P 0.001). Experiments in the models using artificial urine showed that increasing the low fluid intake (720 mL/24 h) characteristic of many patients undergoing long-term catheterization by factors of three and six, significantly (P 0.01) reduced the amounts of calcium and magnesium that formed on catheters. At a simulated fluid intake of 720 mL/24 h, catheters blocked with encrustation after a mean of 42.5 h, while those supplied with urine produced from an intake of 4320 mL/24 h, drained freely for > 10 days.

CONCLUSION: In this in vitro study, drinking cranberry juice did not produce urine that was inhibitory to the development of crystalline catheter-blocking P. mirabilis biofilms. The important factor in preventing catheter encrustation is a high fluid intake.