A clinical assessment of the performance of a sensor to detect crystalline biofilm formation on indwelling bladder catheters.

OBJECTIVES: To test the ability of a sensor developed to signal infection by the organisms that generate the crystalline biofilms that encrust catheters, to give an early warning that encrustation was occurring on patients' catheters, as the care of many patients undergoing long-term bladder catheterization is complicated by the encrustation and blockage of their catheters. PATIENTS AND METHODS: Twenty patients were followed prospectively for the lifetime of one of their catheters. Sensors based on cellulose acetate/bromothymol blue were placed in the urine-collection bags, which were changed as usual at weekly intervals. The bacteriology was assessed and pH determined weekly on urine samples. Photographic records were made of the sensors twice weekly. On removal, each catheter was examined for encrustation and blockage. RESULTS: Proteus mirabilis was not isolated from five patients and in these cases the sensor colour remained golden-yellow to brown. The catheters drained for the scheduled period and showed no signs of encrustation. By contrast, the sensors turned dark blue/black in the urine of all 15 patients infected with P. mirabilis. All these patients' catheters were encrusted and in 12 the catheters blocked. The mean interval between the sensor signalling and the catheter blocking was 12 days. CONCLUSION: The cellulose acetate/bromothymol blue sensors placed in the urine collection bags are capable of signalling infection by P. mirabilis. They also signal the early stages of catheter encrustation and allow catheter replacement in ample time to avoid the clinical crises and emergency referrals caused by catheter blockage.

Quantitative bacterial micro-assay for rapid detection of serum phenylalanine on dry blood-spots: application in phenylketonuria screening.

Phenylketonuria is an inherited metabolic disease, which is characterized by an increased level of serum phenylalanine. Quantitative measurement of phenylalanine in the serum of phenylketonuria patients is necessary to confirm the disease, and to distinguish phenylketonuria from other forms of hyperphenylalaninemia. In this study, we report a rapid and inexpensive micro-assay for simultaneous detection and quantitative measurement of serum phenylalanine on dry blood-spots. Analysis of the standard curve showed a broad linear range for phenylalanine from 120 to 1800 micromol/L. Application of this method, the standard Guthrie bacterial inhibition assay and a high-performance liquid chromatography (HPLC) method for analysis of 34 samples from phenylketonuria patients and control samples produced comparable results, with the regression equation Y = 0.994X + 0.996. The advantage of this method over the Guthrie bacterial inhibition assay is its ability to measure serum phenylalanine quantitatively without false positive results. The method was successfully applied to dried blood-spots, serum and whole blood. The cost per sample is approximately 20-50 US cents, which is much less than for HPLC and commercial enzyme kits. The method can be automated, and is thus suitable for neonatal and mass screening for phenylketonuria, especially in developing countries where funding is a limiting factor.