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Study of the factors that modulate the rate of crystalline Proteus mirabilis biofilm development on urinary catheters

MacLeod, Sarah M. 2006. Study of the factors that modulate the rate of crystalline Proteus mirabilis biofilm development on urinary catheters. PhD Thesis, Cardiff University.

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Around 50% of patients enduring long-term catheterisation experience encrustation and blockage of their catheters. This problem stems from infection by urease producing bacterial species, in particular Proteus mirabilis. The urease enzyme hydrolyses urea to carbon dioxide and ammonia which elevates the urinary pH. Under these alkaline conditions crystals of calcium and magnesium phosphates form and the crystalline bacterial biofilm that develops on the catheter can eventually block the flow of urine through its lumen. Catheter blockage in this way can induce complications that put the health of the patient at serious risk. Currently there are no effective methods for controlling this process and little is known about the bacterial or host factors that might modulate the rate of catheter encrustation. The extent to which catheter biofilms contain potentially dangerous levels of endotoxin is also unknown. In view of the lack of information relating to these issues the objectives of this study were to: (a) gain an insight into the complexity of the urinary flora of patients undergoing long-term catheterisation (b) examine the bacterial composition of catheter biofilms for evidence of antagonisms between Pr. mirabilis and other species (c) test the effects of other uropathogens on the ability of Pr. mirabilis to produce catheter encrustations in laboratory models of the catheterised bladder (d) examine the hypothesis that coaggregation between Pr. mirabilis and other species is involved in the formation of crystalline catheter biofilms and (e) determine whether endotoxin can be found in catheter biofilms from patients undergoing long-term catheterisation. Over a six-week period urine samples were analysed from five patients undergoing long-term catheterisation. The urinary flora was both polymicrobial and dynamic, commonly containing at least four bacterial species. The pH of the urine varied from week to week. The presence of Pr. mirabilis was always associated with alkaline urine (mean pH 8.66). The presence of other urease producing species such as Pseudomonas aeruginosa and Morganella morganii were not associated with highly alkaline urine. In the cases of the four patients who did not suffer from catheter blockages in the study period, the nucleation pH (pHn) of their urine at week six was above the pH of their voided urine (pHv). The only patient in which the pHn was below the pHv had a stable Pr. mirabilis infection and had two catheters block during the study period. A significant negative correlation was found between the urinary concentrations of calcium and magnesium and the nucleation pH value. Strategies to decrease the concentrations of these divalent cations will act to increase the nucleation pH and reduce the rate of crystal accumulation and mineralised bacterial biofilm development. To control catheter encrustation it will be essential to prevent the ability of Pr. mirabilis to elevate the pH of the urine above its nucleation pH. Analysis of the data on 106 catheter biofilm communities from long-term hospital and community-dwelling catheterised individuals revealed that the overall incidence of Pr. mirabilis was 30.19%. Particularly when species such as Klebsiella pneumoniae were recovered from catheters, the percentage incidence of Pr. mirabilis was above this figure. In contrast, when species such as Escherichia coli, Morg. morganii or Enterobacter cloacae were present on a catheter, Pr. mirabilis was rarely or never found. An experimental approach, using laboratory models of the catheterised bladder, was used to investigate the interactions of Pr. mirabilis with the test organisms Et. cloacae, Morg. morganii, Kl. pneumoniae, E. coli, and Ps. aeruginosa in more detail. Experiments in laboratory models showed that super-infection of Pr. mirabilis after 24 h growth of one of each of the test species had little or no effect on the ability of Pr. mirabilis to encrust and block catheters. However, growth of Et. cloacae, Morg. morganii, Kl. pneumoniae, or E. coli for 72 h prior to Pr. mirabilis super-infection significantly delayed catheter blockage. When Pr. mirabilis was inoculated into models 72 h after Et. cloacae for example, the mean time to blockage was extended from 28.74 h to 60.73 h (P < 0.01). In all cases however, Pr. mirabilis was eventually able to generate alkaline urine, induce crystal formation, and block the catheters. Reconstituting a four-member bacterial community from this patient significantly slowed the rise in urinary pH and postponed blockage compared to models infected with the Pr. mirabilis alone. Biofilms on sections of catheters received from patients were found to contain endotoxin levels ranging from 282.8 to 917.2 ng/4 cm length of catheter. The results from this study suggest that antagonistic interactions between Pr. mirabilis and other urinary tract organisms do exist. (Abstract shortened by UMI.)

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Biosciences
Subjects: Q Science > Q Science (General)
ISBN: 9781303208225
Date of First Compliant Deposit: 30 March 2016
Last Modified: 12 Feb 2016 23:15

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