Relationship between Urease‐producing Bacteria, Urinary pH and Encrustation on Indwelling Urinary Catheters

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Abstract
Summary— In 11 patients with long-term indwelling catheters the amount of catheter encrustation and urinary pH were measured and the urine regularly cultured over a prolonged period of time (median of 7 periods of 3 weeks). The mean urinary pH was related to the persistent presence of urease-producing micro-organisms (P. mirabilis) and urinary pH governed the precipitation of catheter encrustation. The critical pH appeared to be around 6.8. In patients with a mean urinary pH below this level the encrustation was minute (≤2.9 mg phosphate). In patients with a mean urinary pH above 6.8 it was considerable but with a marked interindividual variation (35.5–138.7 mg phosphate). The composition of the encrustation was also strongly pH-related, with a much higher proportion present as magnesium ammonium phosphate in patients with a mean urinary pH above 6.8. The persistent presence of urease producers was not associated with a high pH or a more pronounced precipitation of phosphate in all patients. The amount of encrustation thus appears to depend not only on the presence of urease-producing micro-organisms but also on individual factors such as urinary composition.