Prospective study of individuals with long-term urinary catheters colonized with Proteus species

N-acetylcysteine prevents catheter occlusion and inflammation in catheter associated-urinary tract infections by suppressing urease activity

Introduction

Proteus mirabilis is a key pathobiont in catheter-associated urinary tract infections (CA-UTIs), which is well known to form crystalline biofilms that occlude catheters. Urease activity alkylates urine through the release of ammonia, consequentially resulting in higher levels of Mg2+ and Ca2+ and formation of crystals. In this study, we showed that N-acetyl cysteine (NAC), a thiol antioxidant, is a potent urease inhibitor that prevents crystalline biofilm formation.

Methods

To quantify urease activity, Berthelot's method was done on bacterial extracts treated with NAC. We also used an in vitro catheterised glass bladder model to study the effect of NAC treatment on catheter occlusion and biofilm encrustation in P. mirabilis infections. Inductively-coupled plasma mass spectrometry (ICP-MS) was performed on catheter samples to decipher elemental profiles.

Results

NAC inhibits urease activity of clinical P. mirabilis isolates at concentrations as low as 1 mM, independent of bacterial killing. The study also showed that NAC is bacteriostatic on P. mirabilis, and inhibited biofilm formation and catheter occlusion in an in vitro. A significant 4-8log10 reduction in viable bacteria was observed in catheters infected in this model. Additionally, biofilms in NAC treated catheters displayed a depletion of calcium, magnesium, or phosphates (>10 fold reduction), thus confirming the absence of any urease activity in the presence of NAC. Interestingly, we also showed that not only is NAC anti-inflammatory in bladder epithelial cells (BECs), but that it mutes its inflammatory response to urease and P. mirabilis infection by reducing the production of IL-6, IL-8 and IL-1b.

Discussion

Using biochemical, microbiological and immunological techniques, this study displays the functionality of NAC in preventing catheter occlusion by inhibiting urease activity. The study also highlights NAC as a strong anti-inflammatory antibiofilm agent that can target both bacterial and host factors in the treatment of CA-UTIs.

Optimisation of a lozenge-based sensor for detecting impending blockage of urinary catheters

Catheter-associated urinary tract infections resulting from urease-positive microorganisms are more likely to cause a urinary catheter blockage owing to the urease activity of the microbes. Catheter blockage can be dangerous and increases the risk of severe infections, such as sepsis. Ureases, a virulence factor in Proteus mirabilis, cause an increase in urine pH - leading to blockage. An optimised biosensor "lozenge" is presented here, which is able to detect impending catheter blockage. This lozenge has been optimised to allow easy manufacture and commercialisation. It functions as a sensor in a physiologically representative model of a catheterised urinary tract, providing 6.7 h warning prior to catheter blockage. The lozenge is stable in healthy human urine and can be sterilized for clinical use by ethylene oxide. Clinically, the lozenge will provide a visible indication of impending catheter blockage, enabling quicker clinical intervention and thus reducing the morbidity and mortality associated with blockage.

Study of factors influencing the encrustation of indwelling catheters: prospective case series

Background

Long-term catheterisation is frequently necessary for patients with retention of urine or intractable incontinence who are unfit for definitive treatment or being evaluated for definitive treatment. In this study, the important factors influencing the encrustation of indwelling catheters are analysed.

Methods

A total of 52 patients on catheter drainage for a period ranging from 1 month to 1 year were taken in the study. Patients reported either for problems like catheter block or routine changing of catheter. The catheters were removed, and encrustation was subjected to chemical analysis. Urine was examined for pH, specific gravity, culture sensitivity and appearance. Blood samples were taken for estimation of calcium, phosphorus and uric acid.

Results

Out of 52 patients, 28 with urea splitting and 15 with non-urea splitting had positive urine culture (43 out of 52). Amongst 28, 27 (96%) had encrustation compared to 10 (50%) out of 15 with non-urea splitting bacteria (p value < .05). Amongst 24 patients having pH > 6, 22 (92%) had encrustation (p value < .05). The encrustation was found to be more common in bedridden patients (91%) when compared to physically active patients (54%) (p value < .05). The encrustation was more common in patients having single catheter for more than 15 days (86%) when compared to patients having catheter for shorter period (43%) (p value < .05).

Conclusion

This study showed definitive influence of the following factors in encrustation formation: infection with urea splitting organism, alkaline pH, physical activity of patient and duration of keeping a particular catheter.

Urethral Catheter Biofilms Reveal Plasticity in Bacterial Composition and Metabolism and Withstand Host Immune Defenses in Hypoxic Environment

Biofilms composed of multiple microorganisms colonize the surfaces of indwelling urethral catheters that are used serially by neurogenic bladder patients and cause chronic infections. Well-adapted pathogens in this niche are Escherichia coli, Proteus, and Enterococcus spp., species that cycle through adhesion and multilayered cell growth, trigger host immune responses, are starved off nutrients, and then disperse. Viable microbial foci retained in the urinary tract recolonize catheter surfaces. The molecular adaptations of bacteria in catheter biofilms (CBs) are not well-understood, promising new insights into this pathology based on host and microbial meta-omics analyses from clinical specimens. We examined catheters from nine neurogenic bladder patients longitudinally over up to 6 months. Taxonomic analyses from 16S rRNA gene sequencing and liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based proteomics revealed that 95% of all catheter and corresponding urinary pellet (UP) samples contained bacteria. CB biomasses were dominated by Enterobacteriaceae spp. and often accompanied by lactic acid and anaerobic bacteria. Systemic antibiotic drug treatments of patients resulted in either transient or lasting microbial community perturbations. Neutrophil effector proteins were abundant not only in UP but also CB samples, indicating their penetration of biofilm surfaces. In the context of one patient who advanced to a kidney infection, Proteus mirabilis proteomic data suggested a combination of factors associated with this disease complication: CB biomasses were high; the bacteria produced urease alkalinizing the pH and triggering urinary salt deposition on luminal catheter surfaces; P. mirabilis utilized energy-producing respiratory systems more than in CBs from other patients. The NADH:quinone oxidoreductase II (Nqr), a Na+ translocating enzyme not operating as a proton pump, and the nitrate reductase A (Nar) equipped the pathogen with electron transport chains promoting growth under hypoxic conditions. Both P. mirabilis and E. coli featured repertoires of transition metal ion acquisition systems in response to human host-mediated iron and zinc sequestration. We discovered a new drug target, the Nqr respiratory system, whose deactivation may compromise P. mirabilis growth in a basic pH milieu. Animal models would not allow such molecular-level insights into polymicrobial biofilm metabolism and interactions because the complexity cannot be replicated.

In vivo catheterization study of chlorhexidine-loaded nanoparticle coated Foley urinary catheters in male New Zealand white rabbits

Foley urinary catheters were coated with chlorhexidine-loaded nanoparticles (CHX-NPs), encapsulated in the form of micelles and nanospheres. Both of nanoparticles were deposited by multilayer nanocoating through dip and spray coating on the catheter surface both inner and outer surface. In our previous studies, the nanocoating of Foley urinary catheters was studied for chlorhexidine release, degradation, antibacterial evaluation, cytotoxicity assessment, hemocompatibility, skin irritation, skin sensitization, and stability during storage. The results demonstrated the antimicrobial functions and biocompatibility of the coated catheters. In this study, coated urinary catheters were inserted in the bladders of rabbits for 7 day to investigate their efficacy. Histopathology results showed no inflammation, redness, or swelling on bladder and urethra tissues. Surface morphology comparison of uncoated catheters in the control group and coated catheters in the treatment group revealed more encrustation and crystallization on uncoated catheter than on coated catheter, indicating that catheters coated with CHX-NPs showed efficacy in delaying encrustation and bacterial colonization. These findings suggest that nanocoating of urinary catheters can potentially enhance the biocompatibility of medical devices.

Weak organic acid synergy towards the prevention of catheter blockages

BACKGROUND

Up to 50% of all long-term catheterized individuals experience recurrent episodes of urinary catheter infections and blockages, leading to urine retention, pyelonephritis and septicaemia if the catheter is left in situ. We have previously reported the synergistic activity of weak organic acid (WOA) combinations against nosocomial uropathogens.

AIM

To investigate the efficacy of selected WOAs, citric acid and propionic acid, alone and in combination, on prevention of crystalline biofilm formation and catheter blockages.

METHODS

Static crystallization assays and dynamic in vitro bladder model assays, with scanning electron microscopy, were performed for determination of bacterial viability, urinary pH and time to catheter blockage.

FINDINGS

The rate of encrustation around the catheter eyeholes was reduced in the presence of the citric acid/propionic acid combination, extending the time to blockage three-fold.

CONCLUSION

Synergistic WOA combinations identified herein represent promising alternatives to antibiotics to combat the global healthcare burden of catheter-associated urinary tract infections and related blockages.

Pathogen displacement during intermittent catheter insertion: a novel in vitro urethra model

AIM

To develop a novel in vitro urethra model and use it to determine if insertion of an intermittent urinary catheter (IC) displaces pathogenic bacteria from the urethral meatus along the urethra.

METHODS

Displacement of microbial growth after catheter insertion was assessed using a novel in vitro urethra model. The in vitro urethra model utilized chromogenic agar and was inoculated with bacteria at one side of the artificial urethra channel, to act as a contaminated urethral meatus, before an IC was inserted into the channel. Three ICs types were used to validate the in vitro urethra model and methodology.

RESULTS

When compared to the bacterial growth control, a significant difference in bacterial growth was found after insertion of the uncoated (P ≤ 0·001) and hydrophilic coated (P ≤ 0·009) catheters; no significant difference when a prototype catheter was inserted into the in vitro urethra model with either bacterial species tested (P ≥ 0·423).

CONCLUSION

The results presented support the hypothesis that a single catheter insertion can initiate a catheter-associated urinary tract infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

The in vitro urethra model and associated methodology were found to be reliable and reproducible (P ≥ 0·265) providing new research tool for the development and validation of emerging technologies in urological healthcare.

Bacterial biofilm formation on indwelling urethral catheters

Urethral catheters are the most commonly deployed medical devices and used to manage a wide range of conditions in both hospital and community care settings. The use of long-term catheterization, where the catheter remains in place for a period >28 days remains common, and the care of these patients is often undermined by the acquisition of infections and formation of biofilms on catheter surfaces. Particular problems arise from colonization with urease-producing species such as Proteus mirabilis, which form unusual crystalline biofilms that encrust catheter surfaces and block urine flow. Encrustation and blockage often lead to a range of serious clinical complications and emergency hospital referrals in long-term catheterized patients. Here we review current understanding of bacterial biofilm formation on urethral catheters, with a focus on crystalline biofilm formation by P. mirabilis, as well as approaches that may be used to control biofilm formation on these devices. SIGNIFICANCE AND IMPACT OF THE STUDY: Urinary catheters are the most commonly used medical devices in many healthcare systems, but their use predisposes to infection and provide ideal conditions for bacterial biofilm formation. Patients managed by long-term urethral catheterization are particularly vulnerable to biofilm-related infections, with crystalline biofilm formation by urease producing species frequently leading to catheter blockage and other serious clinical complications. This review considers current knowledge regarding biofilm formation on urethral catheters, and possible strategies for their control.

Pathogenesis of Proteus mirabilis Infection

Proteus mirabilis, a Gram-negative rod-shaped bacterium most noted for its swarming motility and urease activity, frequently causes catheter-associated urinary tract infections (CAUTIs) that are often polymicrobial. These infections may be accompanied by urolithiasis, the development of bladder or kidney stones due to alkalinization of urine from urease-catalyzed urea hydrolysis. Adherence of the bacterium to epithelial and catheter surfaces is mediated by 17 different fimbriae, most notably MR/P fimbriae. Repressors of motility are often encoded by these fimbrial operons. Motility is mediated by flagella encoded on a single contiguous 54-kb chromosomal sequence. On agar plates, P. mirabilis undergoes a morphological conversion to a filamentous swarmer cell expressing hundreds of flagella. When swarms from different strains meet, a line of demarcation, a "Dienes line," develops due to the killing action of each strain's type VI secretion system. During infection, histological damage is caused by cytotoxins including hemolysin and a variety of proteases, some autotransported. The pathogenesis of infection, including assessment of individual genes or global screens for virulence or fitness factors has been assessed in murine models of ascending urinary tract infections or CAUTIs using both single-species and polymicrobial models. Global gene expression studies performed in culture and in the murine model have revealed the unique metabolism of this bacterium. Vaccines, using MR/P fimbria and its adhesin, MrpH, have been shown to be efficacious in the murine model. A comprehensive review of factors associated with urinary tract infection is presented, encompassing both historical perspectives and current advances.

Review of Catheter-Associated Urinary Tract Infections and In Vitro Urinary Tract Models

Catheter-associated urinary tract infections (CAUTIs) are one of the most common nosocomial infections and can lead to numerous medical complications from the mild catheter encrustation and bladder stones to the severe septicaemia, endotoxic shock, and pyelonephritis. Catheters are one of the most commonly used medical devices in the world and can be characterised as either indwelling (ID) or intermittent catheters (IC). The primary challenges in the use of IDs are biofilm formation and encrustation. ICs are increasingly seen as a solution to the complications caused by IDs as ICs pose no risk of biofilm formation due to their short time in the body and a lower risk of bladder stone formation. Research on IDs has focused on the use of antimicrobial and antibiofilm compounds, while research on ICs has focused on preventing bacteria entering the urinary tract or coming into contact with the catheter. There is an urgent need for in vitro urinary tract models to facilitate faster research and development for CAUTI prevention. There are currently three urinary tract models that test IDs; however, there is only a single very limited model for testing ICs. There is currently no standardised urinary tract model to test the efficacies of ICs.

Development of an Infection-Responsive Fluorescent Sensor for the Early Detection of Urinary Catheter Blockage

Formation of crystalline biofilms following infection by Proteus mirabilis can lead to encrustation and blockage of long-term indwelling catheters, with serious clinical consequences. We describe a simple sensor, placed within the catheter drainage bag, to alert of impending blockage via a urinary color change. The pH-responsive sensor is a dual-layered polymeric "lozenge", able to release the self-quenching dye 5(6)-carboxyfluorescein in response to the alkaline urine generated by the expression of bacterial urease. Sensor performance was evaluated within a laboratory model of the catheterized urinary tract, infected with both urease positive and negative bacterial strains under conditions of established infection, achieving an average "early warning" of catheter blockage of 14.5 h. Signaling only occurred following infection with urease positive bacteria. Translation of these sensors into a clinical environment would allow appropriate intervention before the occurrence of catheter blockage, a problem for which there is currently no effective control method.

An in-situ infection detection sensor coating for urinary catheters

We describe a novel infection-responsive coating for urinary catheters that provides a clear visual early warning of Proteus mirabilis infection and subsequent blockage. The crystalline biofilms of P. mirabilis can cause serious complications for patients undergoing long-term bladder catheterisation. Healthy urine is around pH 6, bacterial urease increases urine pH leading to the precipitation of calcium and magnesium deposits from the urine, resulting in dense crystalline biofilms on the catheter surface that blocks urine flow. The coating is a dual layered system in which the lower poly(vinyl alcohol) layer contains the self-quenching dye carboxyfluorescein. This is capped by an upper layer of the pH responsive polymer poly(methyl methacrylate-co-methacrylic acid) (Eudragit S100®). Elevation of urinary pH (>pH 7) dissolves the Eudragit layer, releasing the dye to provide a clear visual warning of impending blockage. Evaluation of prototype coatings using a clinically relevant in vitro bladder model system demonstrated that coatings provide up to 12 h advanced warning of blockage, and are stable both in the absence of infection, and in the presence of species that do not cause catheter blockage. At the present time, there are no effective methods to control these infections or provide warning of impending catheter blockage.

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Development of a dual-layered diagnostic coating sensor for urinary catheter.

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Provides advance warning of infection by P. mirabilis in response to alkaline urine.

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Read out via release of carboxyfluorescein dye from coating into urine leg bag.

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Catheter prototypes ‘report’ infection 12 h before blockage by P. mirablis.

Clinical complications of urinary catheters caused by crystalline biofilms: something needs to be done

This review is largely based on a previous paper published in the journal Spinal Cord. The care of many patients undergoing long-term bladder catheterization is complicated by encrustation and blockage of their Foley catheters. This problem stems from infection by urease-producing bacteria, particularly Proteus mirabilis. These organisms colonize the catheter forming an extensive biofilm; they also generate ammonia from urea, thus elevating the pH of urine. As the pH rises, crystals of calcium and magnesium phosphates precipitate in the urine and in the catheter biofilm. The continued development of this crystalline biofilm blocks the flow of urine through the catheter. Urine then either leaks along the outside of the catheter and the patient becomes incontinent or is retained causing painful distension of the bladder and reflux of urine to the kidneys. The process of crystal deposition can also initiate stone formation. Most patients suffering from recurrent catheter encrustation develop bladder stones. P. mirabilis establishes stable residence in these stones and is extremely difficult to eliminate from the catheterized urinary tract by antibiotic therapy. If blocked catheters are not identified and changed, serious symptomatic episodes of pyelonephritis, septicaemia and endotoxic shock can result. All types of Foley catheters including silver- or nitrofurazone-coated devices are vulnerable to this problem. In this review, the ways in which biofilm formation on Foley catheters is initiated by P. mirabilis will be described. The implications of understanding these mechanisms for the development of an encrustation-resistant catheter will be discussed. Finally, the way forward for the prevention and control of this problem will be considered.

Addressing the problems of long-term urethral catheterization: part 2

This is the second of a two-part article and addresses the problems encountered throughout the life of a catheter from those relating to its insertion, through the time when it is in situ, to those associated with its removal. Catheters can cause discomfort and reasons for this are discussed including latex allergy, atrophic changes in women, blockage or bypass. The draft National Institute for Health and Clinical Excellence infection control guidance is discussed with reference to catheter maintenance solutions. Sexuality can be an unvoiced concern to patients with catheters in situ and clinicians are encouraged to discuss such issues with the patient, where relevant. Issues including catheter expulsion, bladder spasm and difficulties in catheter removal, including the non-deflating balloon and cuffing are addressed. The article concludes that although every patient is an individual with a unique set of problems, learning how to address one series of difficulties will help when dealing with subsequent challenges.

The encrustation and blockage of long-term indwelling bladder catheters: a way forward in prevention and control

OBJECTIVES

To review the literature showing that understanding how Foley catheters become encrusted and blocked by crystalline bacterial biofilms has led to strategies for the control of this complication in the care of patients undergoing long-term indwelling bladder catheterization.

METHODS

A comprehensive PubMed search of the literature published between 1980 and December 2009 was made for relevant articles using the Medical Subject Heading terms 'biofilms', 'urinary catheterization', 'catheter-associated urinary tract infection' and 'urolithiasis'. Papers on catheter-associated urinary tract infections and bacterial biofilms collected during 40 years of working in the field were also reviewed.

RESULTS

There is strong experimental and epidemiological evidence that infection by Proteus mirabilis is the main cause of the crystalline biofilms that encrust and block Foley catheters. The ability of P. mirabilis to generate alkaline urine and to colonize all available types of indwelling catheters allows it to take up stable residence in the catheterized tract in bladder stones and cause recurrent catheter blockage.

CONCLUSION

The elimination of P. mirabilis by antibiotic therapy as soon as it appears in the catheterized urinary tract could improve the quality of life for many patients and reduce the current expenditure of resources when managing the complications of catheter encrustation and blockage. For patients who are already chronic blockers and stone formers, antibiotic treatment is unlikely to be effective owing to the resistance of cells in the crystalline biofilms. Strategies such as increasing fluid intake with citrated drinks could control the problem until bladder stone removal can be organized.

Strategy to control catheter encrustation with citrated drinks: a randomized crossover study

PURPOSE

Nucleation pH is the pH at which Ca and Mg come out of urine to form crystals. If the safety margin between voiding pH and nucleation pH could be increased, it would increase the possibility of an alternative to controlling the activity of urease producing bacteria as a strategy to control catheter encrustation.

MATERIALS AND METHODS

We performed a 6-week randomized crossover study in 24 patients with catheter blockage who were randomly allocated to a specific sequence of 3 consecutive available treatments, including increased fluid intake, lemon juice and potassium citrate. Each patient received all available regimens. At the end of each week 24-hour urine samples were analyzed for voiding and nucleation pH, citrate, Ca and Mg.

RESULTS

Mean +/- SD nucleation pH increased from 7.45 +/- 0.60 at baseline to 7.93 +/- 0.50, 7.68 +/- 0.64 and 7.96 +/- 0.37 in the lemon juice, increased fluid intake and potassium citrate groups, respectively (p <0.0001). Mean urinary citrate increased significantly (p <0.0001), in particular due to lemon juice and potassium citrate effects. The association between treatment and Ca was weak (p = 0.12) while that of Mg was negative due to lemon (p <0.001). Average increase in the safety margin (nucleation pH minus voiding pH) beyond baseline was 0.84 (95% CI 0.63-1.04), 0.57 (95% CI 0.37-0.78) and 0.41 (95% CI 0.20-0.61) for lemon juice, increased fluid intake and potassium citrate, respectively. A strong treatment effect on the safety margin was apparent even when controlling for study design (p <0.001).

CONCLUSIONS

Increased fluid intake with lemon juice may be a simple, inexpensive, effective strategy to control catheter encrustation.

Crystalline bacterial biofilm formation on urinary catheters by urease-producing urinary tract pathogens: a simple method of control

The problem of catheter encrustation stems from infection by urease-producing bacteria. These organisms generate ammonia from urea, elevate the pH of urine and cause crystals of calcium and magnesium phosphates to form in the urine and the biofilm that develops on the catheter. In this study, a laboratory model was used to compare the ability of 12 urease-positive species of urinary tract pathogens to encrust and block catheters. Proteus mirabilis, Proteus vulgaris and Providencia rettgeri were able to raise the urinary pH above 8.3 and produce catheter-blocking crystalline biofilms within 40 h. Morganella morganii and Staphylococcus aureus elevated the pH of urine to 7.4 and 6.9, respectively, and caused some crystal deposition in the biofilms but did not block catheters in the 96 h experimental period. Isolates of Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, Serratia marcescens, Pseudomonas aeruginosa and Providencia stuartii were only capable of raising the pH of urine to a maximum of 6.4 and failed to cause crystal deposition in the biofilm. The most effective way to prevent catheter encrustation was shown to be diluting urine and increasing its citrate concentration. This strategy raises the nucleation pH (pH(n)) at which calcium and magnesium phosphates crystallize from urine. Increasing the fluid intake of a healthy volunteer with citrated drinks resulted in urine with a pH(n) of >8.0 in which catheter encrustation was inhibited. It is suggested that this dietary strategy will be an effective means of controlling catheter encrustation, whichever bacterial species is causing the problem.

Bacterial biofilms in patients with indwelling urinary catheters

Bacteria have a basic survival strategy: to colonize surfaces and grow as biofilm communities embedded in a gel-like polysaccharide matrix. The catheterized urinary tract provides ideal conditions for the development of enormous biofilm populations. Many bacterial species colonize indwelling catheters as biofilms, inducing complications in patients' care. The most troublesome complications are the crystalline biofilms that can occlude the catheter lumen and trigger episodes of pyelonephritis and septicemia. The crystalline biofilms result from infection by urease-producing bacteria, particularly Proteus mirabilis. Urease raises the urinary pH and drives the formation of calcium phosphate and magnesium phosphate crystals in the biofilm. All types of catheter are vulnerable to encrustation by these biofilms, and clinical prevention strategies are clearly needed, as bacteria growing in the biofilm mode are resistant to antibiotics. Evidence indicates that treatment of symptomatic, catheter-associated urinary tract infection is more effective if biofilm-laden catheters are changed before antibiotic treatment is initiated. Infection with P. mirabilis exposes the many faults of currently available catheters, and plenty of scope exists for improvement in both their design and production; manufacturers should take up the challenge to improve patient outcomes.

Observations on the development of the crystalline bacterial biofilms that encrust and block Foley catheters

The care of many patients undergoing long-term bladder catheterisation is complicated when the flow of urine through the catheter is blocked by encrustation. The problem results from infection by urease-producing bacteria, especially Proteus mirabilis, and the subsequent formation of crystalline biofilms on the catheter. The aim of this study was to discover how P. mirabilis initiates the development of these crystalline biofilms. The early stages in the formation of the biofilms were observed on a range of Foley catheters in a laboratory model of the catheterised bladder. Scanning electron micrographs revealed that when all-silicone, silicone-coated latex, hydrogel-coated latex, hydrogel/silver-coated latex and nitrofurazone silicone catheters were inserted into bladder models containing P. mirabilis and alkaline urine, their surfaces were rapidly coated with a microcrystalline foundation layer. X-ray microanalysis showed that this material was composed of calcium phosphate. Bacterial colonisation of the foundation layer followed and by 18h the catheters were encrusted by densely populated crystalline P. mirabilis biofilms. These observations have important implications for the development of encrustation-resistant catheters. In the case of silver catheters for example, bacterial cells can attach to the crystalline foundation layer and continue to grow, protected from contact with the underlying silver. If antimicrobials are to be incorporated into catheters to prevent encrustation, it is important that they diffuse into the urine and prevent the rise in pH that triggers crystal formation.

Urinary catheter use in older people

Long-term indwelling urinary catheters can be an effective means of managing bladder dysfunction for some older people, where alternative strategies are unsuitable or unsatisfactory, and where careful assessment of the patient and their particular problem has been undertaken. However, catheter-associated risks are well known and, consequently, catheters should be avoided wherever possible. Although prevalence of catheterization varies widely in different settings and different cultures of care, there is evidence that many older people are catheterized inappropriately and also remain catheterized unnecessarily. This paper discusses issues to be considered in decision-making processes regarding long-term catheterization. It examines catheter-associated problems, their management and factors influencing the quality of evidence to guide clinical practice.

Some Observations on the Diffusion of Antimicrobial Agents Through the Retention Balloons of Foley Catheters

PURPOSE

We examined the ability of antimicrobial agents to diffuse through the retention balloons of urinary catheters and inhibit their encrustation by Proteus mirabilis.

MATERIALS AND METHODS

An agar diffusion screening test was developed to detect agents capable of diffusing through catheter balloons and inhibiting the growth of P. mirabilis. The effect of inflating the balloons with antibacterials on the ability of P. mirabilis to encrust catheters was tested in laboratory models of the catheterized bladder.

RESULTS

Of 18 antimicrobial agents active on P. mirabilis only mandelic acid, phenoxyethanol, nalidixic acid and triclosan diffused through all-silicone catheter balloons to produce zones of inhibition against P. mirabilis. Polyurethane balloons were permeable to gentamicin and fluoroquinolones. Experiments with silicone catheters showed that inflating balloons with mandelic acid (100 gm/l) or ciprofloxacin (10 gm/l) failed to extended the time at which catheters became blocked in models inoculated with P. mirabilis. However, nalidixic acid (50 gm/l) significantly extended the lifespan of catheters (p <0.05). Triclosan (10 gm/l) prevented the increase in urinary pH that induces crystal formation and inhibited the formation of crystalline biofilm, enabling the catheters to drain freely for the full 7-day experimental period.

CONCLUSIONS

Inflation of silicone catheter retention balloons with solutions of nalidixic acid or triclosan rather than water should be considered as strategies to control catheter encrustation. Polyurethane balloons are more permeable than silicone balloons to gentamicin and the fluoroquinolones, and they should be investigated as an alternative to silicone or latex in catheter manufacture.

Strategies for the development of the urinary catheter

Indwelling urinary catheters are utilized in the management of a wide range of conditions both in an acute and a chronic setting. However, utilization of this type of device is associated with a number of issues, including an increased propensity to develop bacteriuria, symptomatic infection and also encrusted deposits on the device. The development of novel biomaterials, incorporation of therapeutic agents and other strategies to minimize the issues associated with these devices are discussed in this review.

Structure of Proteus mirabilis biofilms grown in artificial urine and standard laboratory media

Proteus mirabilis is a urinary pathogen that can differentiate from a swimmer cell into a swarmer cell morphotype and can form biofilms on the surfaces of urinary catheters. These biofilms block these catheters due to crystals trapped within these structures. The effect of encrustation on biofilm formation and structure has not been studied using confocal scanning laser microscopy (CSLM). Therefore, a comparison of biofilm structure in artificial urine (AU) and laboratory media was undertaken. We compared the structure of P. mirabilis biofilms in AU and Luria-Bertani broth using CSLM and 3D imaging. Biofilms grown in Luria-Bertani broth formed mushroom structures at 24 h and contained nutrient channels. AU biofilms were observed to form a different structure at 24 h. AU biofilm structure was observed to be a flat layer, almost devoid of nutrient channels. Swarmer cells were observed protruding out of the biofilm into the bulk fluid. This could be due to nutrient depravation within the biofilm or a means of further colonizing the surface. This study has demonstrated that two markedly different biofilm structures are formed, depending on the growth media utilized.

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.

Modulation of crystalline Proteus mirabilis biofilm development on urinary catheters

The crystalline biofilms formed by Proteus mirabilis can seriously complicate the care of patients undergoing long-term bladder catheterization. The generation of alkaline urine by the bacterial urease causes calcium and magnesium phosphates to precipitate from urine and accumulate in the catheter biofilm, blocking the flow of urine from the bladder. The pH at which these salts crystallize from a urine sample, the nucleation pH (pH(n)), can be elevated by diluting the urine and by increasing its citrate content. The aim of this study was to examine whether manipulation of pH(n) in these ways modulated the rate at which crystalline biofilm developed. Experiments in laboratory models of the catheterized bladder infected with P. mirabilis showed that when the bladder was supplied with a concentrated urine (pH(n) 6.7) at a low fluid output (720 ml per 24 h), catheters blocked at 19-31 h. Diluting this urine 1:4 increased the pH(n) to 7.5 and models supplied with this urine at 2880 ml per 24 h took 110-137 h to block. When models were supplied with urine containing citrate at 1.5 mg ml(-1) or above (pH(n) 8.3-9.1), the catheters drained freely for the full 7 day experimental period. Scanning electron microscopy revealed that the catheter biofilms that developed in urine with high pH(n) values were devoid of crystalline formations. These observations should encourage a clinical trial to examine the effect of increasing a patient's fluid intake with citrate-containing drinks on the encrustation and blockage of catheters.

Factors affecting crystal precipitation from urine in individuals with long-term urinary catheters colonized with urease-positive bacterial species

Weekly urinalysis was conducted for 12 weeks on a group of 21 long-term catheter users with confirmed catheter encrustation and urinary tract colonization with urease-positive bacteria, in order to explore the cause of considerable variation in the severity of encrustation between sufferers. The rapidity of catheter blockage correlated significantly with the pH above which crystals precipitated from urine (the nucleation pH) but not the pH of the voided urine itself. Linear regression showed the nucleation pH to be significantly predicted by a combination of urinary calcium and magnesium concentrations, with calcium being the more influential variable. Reducing the rate of catheter encrustation could be achieved by lowering the urinary concentration of calcium and magnesium, which may only require catheter users to increase their fluid intake.

Action of ciprofloxacin on planktonic bacteria and biofilm of Proteus mirabilis

Proteus mirabilis can persist in biofilms, with the bacteria in this state tending to resist antibiotic therapy. Until now, the relationship between the action of ciprofloxacin and the production of reactive oxygen species (ROS) has not been studied in planktonic and biofilmic P. mirabilis. Our results show that ciprofloxacin stimulates the production of ROS in planktonic P. mirabilis, but that the increase in ROS was observed in sensitive strains (n = 4) only in the absence of the extracellular matrix (ECM). This augmentation of ROS was principally intracellular, invoking an increase in intracellular superoxide dismutase (SOD). ROS were assayed by chemiluminescence (CL) and SOD by inhibition of reduction of nitroblue tetrazolium in the presence of methionine, riboflavin and light. The antibiotic-resistant strains (n = 4) did not suffer oxidative stress and exhibited a higher antioxidant capacity than antibiotic-sensitive ones, as indicated by tripyridyltriazine assay. Both types of bacterial strain showed a reduction in antioxidant capacity in the presence of ciprofloxacin, and only the resistant bacteria returned to normal count levels within 5 min of introduction of antibiotic. Ciprofloxacin stimulated ROS more than it did nitric oxide (NO) in planktonic bacteria, as determined by Griess's reaction. Proteus mirabilis biofilms treated with ciprofloxacin did not suffer any increase in ROS but there was an increase in NO and the ratio of intracellular ROS:NO decreased to 25%. Biofilms of P. mirabilis were neither stressed nor inhibited by 40 µg ciprofloxacin/ml, a dose higher than the minimum inhibitory concentration (i.e. supra MIC). Both resistant and sensitive strains maintained the number of viable bacteria in biofilms incubated with supra MIC ciprofloxacin at concentrations that stressed and reduced substantially the number of colony-forming units of planktonic bacteria per millilitre. These results contribute to understanding of the differences between biofilmic and planktonic bacteria, with respect to susceptibility to oxidative stress caused by ciprofloxacin and also the antioxidant effect of ECM.