Blockage of urinary catheters: role of microorganisms and constituents of the urine on formation of encrustations.

Long-term indwelling urinary catheters may become blocked in some patients by formation of encrustations made up of aggregated struvite crystals while other patients rarely develop blocked catheters. We have designated these groups as "blockers", "intermediates" or "non-blockers". To further understand this phenomenon we followed 32 catheterized elderly women in a nursing home. Catheters were changed six times at 2 week intervals. Patients tended to remain as "blockers", "intermediates" or "non-blockers" consistently over time. There were no significant differences in use of antibiotics, clinical manifestations of urinary infection or fever among the groups. "Blockers" were significantly more often colonized with Proteus mirabilis and Providencia stuartii than "non-blockers", and significantly less often with Klebsiella pneumoniae. However, there was no evidence of interference among the organisms. "Blockers" excreted a significantly more alkaline urine, and lesser amounts of magnesium, urea and phosphate in their urine. Two "blockers" in whom Proteus sp. were eliminated by coincidental antimicrobial therapy converted to "non-blockers". These findings support the concept that "blockers" are patients who have prolonged colonization with urease producing Proteus mirabilis and Providencia stuartii.