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Title: Study of the development of crystalline Proteus mirabilis biofilms on urinary catheters
Author: Morgan, Sheridan David
ISNI:       0000 0004 2750 4516
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2007
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Infection by Proteus mirabilis can seriously complicate the care of patients undergoing long-term indwelling bladder catheterisation. The urease-producing bacteria colonize the catheter surfaces forming extensive biofilm communities and are capable of generating ammonia from urea and elevating the pH of the urine and biofilm. Under these conditions crystals of calcium and magnesium phosphates form in the urine and within the bacterial biofilm on the indwelling device leading to its encrustation and blockage. Urine can leak around the outside of the blocked catheter and patients become incontinent. Alternatively, urine is retained within the bladder, causing painful distension of the bladder. Reflux of infected urine to the kidneys can lead to serious symptomatic episodes such as pyelonephritis, septicaemia and endotoxic shock. All available types of indwelling catheter are vulnerable to this problem and currently there are no effective procedures available for its control. While the basic mechanism has been established for catheter encrustation we still need to know more about some of the fundamental aspects of the process. Little is known about the early events and the precise mechanisms which P. mirabilis uses to colonize catheter surfaces. The factors that control the rate at which crystalline biofilm forms on the catheters are also unknown. The aims of this study were to establish the sequence of events in the early stages of crystalline P. mirabilis biofilm formation on the range of currently available catheters for use with patients to determine the role of Mannose-Resistant Proteus-hkc fimbriae (MR/P fimbriae) in P. mirabilis crystalline biofilm formation on catheters to investigate how the pH at which calcium and magnesium phosphates precipitate from urine, the nucleation pH (pHn) can be manipulated and to determine the effect of this parameter on the rate of catheter encrustation. Using a laboratory model of the catheterised bladder, scanning electron microscopy and X-ray microanalysis, the initial stages of P. mirabilis crystalline biofilm development was observed on catheter surfaces. All-silicone, silicone-coated latex, hydrogel-coated latex and hydrogel/silver-coated latex catheters rapidly acquired a microcrystalline 'foundation layer' comprised predominantly of calcium phosphate, upon which, P. mirabilis crystalline biofilm subsequently developed. A similar 'foundation layer' was observed on the encrusted surfaces of hydrogel/silver-coated catheters removed from long-term catheterised patients. The catheters impregnated with nitrofurazone briefly delayed the onset of crystalline biofilm formation, while all-silicone and hydrogel-coated latex catheters inflated with triclosan (3 mg/ml in Na2C03) were able to maintain acidic urine pH and prevent crystalline biofilm development for the 7 day experimental period. There is evidence that MR/P fimbriae are involved in initiating infection in non-catheterised urinary tracts. The role of these adhesins in crystalline biofilm formation on indwelling catheters however, has not been investigated. Using bladder models infected with a wild type P. mirabilis strain able to express MR/P fimbriae and its derived MR/P-negative mutant, time to catheter blockage experiments and scanning electron microscopy revealed that MR/P fimbriae were not essential for P. mirabilis colonization of catheter surfaces or the development of crystalline P. mirabilis biofilm. Although the wild type and mutant strain initiated biofilm formation in different ways both rapidly blocked all-silicone catheters with crystalline material. The overriding factor in catheter blockage was the generation of alkaline urine, raising the pH above that at which crystalline formations develop. Previously it has been demonstrated that the pHn of human urine can be elevated by dilution and by increasing its citrate content. In the present study the effect of dilution and adding citrate on the pHn of artificial was assessed. Furthermore, the effect on the rate of encrustation on all-silicone catheters was examined in laboratory models supplied with these urines and infected with urease-positive P. mirabilis, Providencia rettgeri and Proteus vulgaris. The pHn of urine could be elevated from pH 6.7 in neat urine to pH 8.4 in urine diluted to 1:6. When neat, 1:1, 1:2 and 1:3 diluted urines were supplied to bladder models significant increases in catheter lifespan were recorded at each ascending dilution. Increasing the citrate content of the 1:1 diluted urine from 0 to 3.0 g/L citrate elevated the pHn from pH 7 to pH 9.1. Scanning electron microscopy of catheter sections revealed crystalline material in the biofilms could be virtually eliminated for at least 7 days in models supplied with urine with pHns of >pH 8.5. Time to catheter blockage experiments showed the rate of catheter encrustation became significantly reduced as the pHn of urine increased. Catheters in models supplied with urine containing citrate concentrations of 1.5 mg/ml (pHn >8.4) or more drained freely for the whole 7-day experimental period.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available