Proteus mirabilis biofilm protection against struvite crystal dissolution and its implications in struvite urolithiasis

Association among biofilm formation, virulence gene expression, and antibiotic resistance in Proteus mirabilis isolates from diarrhetic animals in Northeast China

Background

The aim of this study was to investigate the association among biofilm formation, virulence gene expression, and antibiotic resistance in P. mirabilis isolates collected from diarrhetic animals (n = 176) in northeast China between September 2014 and October 2016.

Results

Approximately 92.05% of the isolates were biofilm producers, whereas 7.95% of the isolates were non-producers. The prevalence of virulence genes in the biofilm producer group was significantly higher than that in the non-producer group. Biofilm production was significantly associated with the expression of ureC, zapA, rsmA, hmpA, mrpA, atfA, and pmfA (P < 0.05). The results of drug susceptibility tests revealed that approximately 76.7% of the isolates were multidrug-resistant (MDR) and extensively drug-resistant (XDR). Biofilm production was significantly associated with resistance to doxycycline, tetracycline, sulfamethoxazole, kanamycin, and cephalothin (P < 0.05). Although the pathogenicity of the biofilm producers was stronger than that of the non-producers, the biofilm-forming ability of the isolates was not significantly associated with morbidity and mortality in mice (P > 0.05).

Conclusion

Our findings suggested that a high level of multidrug resistance in P. mirabilis isolates obtained from diarrhetic animals in northeast China. The results of this study indicated that the positive rates of the genes expressed by biofilm-producing P. mirabilis isolates were significantly higher than those expressed by non-producing isolates.

Current insights into the mechanisms and management of infection stones

Infection stones are complex aggregates of crystals amalgamated in an organic matrix that are strictly associated with urinary tract infections. The management of patients who form infection stones is challenging owing to the complexity of the calculi and high recurrence rates. The formation of infection stones is a multifactorial process that can be driven by urine chemistry, the urine microenvironment, the presence of modulator substances in urine, associations with bacteria, and the development of biofilms. Despite decades of investigation, the mechanisms of infection stone formation are still poorly understood. A mechanistic understanding of the formation and growth of infection stones - including the role of organics in the stone matrix, microorganisms, and biofilms in stone formation and their effect on stone characteristics - and the medical implications of these insights might be crucial for the development of improved treatments. Tools and approaches used in various disciplines (for example, engineering, chemistry, mineralogy, and microbiology) can be applied to further understand the microorganism-mineral interactions that lead to infection stone formation. Thus, the use of integrated multidisciplinary approaches is imperative to improve the diagnosis, prevention, and treatment of infection stones.

Ureases as a target for the treatment of gastric and urinary infections

Urease is known to be a major contributor to pathologies induced by Helicobacter pylori and Proteus species. In H pylori, urease allows the bacteria to survive in an acidic gastric environment during colonisation, playing an important role in the pathogenesis of gastric and peptic ulcers. Ureolytic activity also results in the production of ammonia in close proximity to the gastric epithelium, causing cell damage and inflammation. In the case of Proteus species (notably Proteus mirabilis) infection, stones are formed due to the presence of ammonia and carbon dioxide released by urease action. In addition, the ammonia released is able to damage the glycosaminoglycan layer, which protects the urothelial surface against bacterial infection. In this context, the administration of urease inhibitors may be an effective therapy for urease-dependent pathogenic bacteria. This is a review of the role of ureases in H pylori and Proteus species infections, focussing on the biochemical and clinical aspects of the most promising and/or potent urease inhibitors for the treatment of gastric and urinary tract infections.

Complicated catheter-associated urinary tract infections due to Escherichia coli and Proteus mirabilis

Catheter-associated urinary tract infections (CAUTIs) represent the most common type of nosocomial infection and are a major health concern due to the complications and frequent recurrence. These infections are often caused by Escherichia coli and Proteus mirabilis. Gram-negative bacterial species that cause CAUTIs express a number of virulence factors associated with adhesion, motility, biofilm formation, immunoavoidance, and nutrient acquisition as well as factors that cause damage to the host. These infections can be reduced by limiting catheter usage and ensuring that health care professionals correctly use closed-system Foley catheters. A number of novel approaches such as condom and suprapubic catheters, intermittent catheterization, new surfaces, catheters with antimicrobial agents, and probiotics have thus far met with limited success. While the diagnosis of symptomatic versus asymptomatic CAUTIs may be a contentious issue, it is generally agreed that once a catheterized patient is believed to have a symptomatic urinary tract infection, the catheter is removed if possible due to the high rate of relapse. Research focusing on the pathogenesis of CAUTIs will lead to a better understanding of the disease process and will subsequently lead to the development of new diagnosis, prevention, and treatment options.

Observations on the adherence of Proteus mirabilis onto polymer surfaces

AIMS

Infection of the catheterized urinary tract with Proteus mirabilis causes blockage of the catheter by crystalline bacterial biofilms. The aim of this work is to identify a surface-coating for catheters that is not vulnerable to colonization by Pr. mirabilis.

METHODS AND RESULTS

A parallel-plate flow-cell and phase contrast microscopy were used to follow bacterial adhesion onto polymer films. Experiments with a urease-negative mutant of Pr. mirabilis suspended in buffer or urine, identified agarose as a polymer on which biofilm did not form. In tests with wild-type urease-producing cells in urine, no adhesion of cells onto agarose was observed for 3 h but then as the pH rose above 8.2, the surface rapidly became colonized by crystalline biofilm.

CONCLUSIONS

In urine at pH below 8.0, Pr. mirabilis does not adhere to agarose-coated surfaces. When the pH rises above 8.2, however, aggregates of crystals and bacteria form in the urine and are deposited on such surfaces.

SIGNIFICANCE AND IMPACT OF THE STUDY

Strategies to prevent the formation of crystalline biofilms on urinary catheters will need to consider both the properties of the surface-coatings and the requirement to prevent the alkaline conditions that induce crystal formation in urine.

Biofilm: its relevance in kidney disease

Biofilm/bioslime is a complex, dynamically interactive multicellular community protected within a heterogeneous exopolysaccharide matrix. Its formation results in the genesis or perpetuation of infection, enhancement of inflammation, and tissue damage or death. Industrial financial losses result from biofilm/bioslime formation; however, the consequences in the medical realm are equally devastating. The relation of biofilm to patients with chronic kidney disease is often covert and extends beyond the colonization of hemodialysis circuits and vascular accesses. Urinary tract device- and vascular access-related biofilms may also increase the burden of cardiovascular risk borne by chronic kidney disease patients, synergizing with the chronic inflammatory state already incurred by these individuals. Current anti-infective strategies are aimed at rapidly killing planktonic forms of microorganisms without specifically targeting the sessile forms that perpetuate their planktonic brethren. Future treatments of infections must ultimately target these reservoirs of infection aiming for their complete eradication. Presently, included among these novel weapons of microdestruction are molecular blockading techniques, electrical enhancement of anti-infectives, and bacterial interference. Nonetheless, the best approach against biofilm formation remains the prevention of microbial colonization, which can be largely by sterile handling of patient-related devices, the most well-established biofilm reservoirs.

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.

Mannose-resistant Proteus-like fimbriae are produced by most Proteus mirabilis strains infecting the urinary tract, dictate the in vivo localization of bacteria, and contribute to biofilm formation

Proteus mirabilis, an etiologic agent of complicated urinary tract infections, expresses mannose-resistant Proteus-like (MR/P) fimbriae whose expression is phase variable. Here we examine the role of these fimbriae in biofilm formation and colonization of the urinary tract. The majority of wild-type P. mirabilis cells in transurethrally infected mice produced MR/P fimbriae. Mutants that were phase-locked for either constitutive expression (MR/P ON) or the inability to express MR/P fimbriae (MR/P OFF) were phenotypically distinct and swarmed at different rates. The number of P. mirabilis cells adhering to bladder tissue did not appear to be affected by MR/P fimbriation. However, the pattern of adherence to the bladder surface was strikingly different. MR/P OFF colonized the lamina propria underlying exfoliated uroepithelium, while MR/P ON colonized the luminal surfaces of bladder umbrella cells and not the exfoliated regions. Wild-type P. mirabilis was usually found colonizing intact uroepithelium, but it occasionally adhered to exfoliated areas. MR/P ON formed significantly more biofilm than either P. mirabilis HI4320 (P = 0.03) or MR/P OFF (P = 0.05). MR/P OFF was able to form a biofilm similar to that of the wild type. MR/P ON formed a three-dimensional biofilm structure as early as 18 h after the initiation of the biofilm, while MR/P OFF and the wild type did not. After 7 days, however, P. mirabilis HI4320 formed a 65-mum-thick biofilm, while the thickest MR/P ON and MR/P OFF biofilms were only 12 mum thick. We concluded that MR/P fimbriae are expressed by most P. mirabilis cells infecting the urinary tract, dictate the localization of bacteria in the bladder, and contribute to biofilm formation.

Isolation of lacZ fusions to Proteus mirabilis genes regulated by intercellular signaling: potential role for the sugar phosphotransferase (Pts) system in regulation

Using a mini-Tn5lacZ1 reporter transposon, lacZ fusions have been identified in Proteus mirabilis that are activated by the accumulation of self-produced extracellular signals. Genes identified by this approach include putative homologs of pgm, nlpA and two genes of unknown function. The extracellular signal(s) involved in activation were resistant to the effects of acid and alkali. The signal required for activation of (nlpA) cma482::lacZ was sensitive to protease, suggesting the signal is a peptide or small protein. The signals behaved as polar molecules and were not extractable with ethyl acetate. A mini-Tn5Cm insertion was identified in a probable ptsI homolog that blocked activation of the cma134::lacZ fusion by an extracellular signal. The ptsI mutation did not alter extracellular signal production and may have a role in signal response.

Uropathogens and urinary tract concretion formation and catheter encrustations

Infection stones (ammonium magnesium phosphate) and catheter encrustations have a common cause-urease producing microorganisms. With their rapid growth and frequent recurrences, infection stones are among the most troublesome of urinary system stones. For many patients with a long-term indwelling catheter, encrustations can be a severe problem. Urine composition is important, because, urine calcium enhances the crystallization process and urine citrate inhibits it. The role of non-urease producing microorganisms in stone forming processes is not well understood. Stones can now be successfully treated with a low morbidity index by percutaneous stone surgery or extracorporeal shock wave lithotripsy (ESWL) and recurrence of stone formation is then avoided by prolonged antibiotic treatment and oral citrate. Catheter encrustations and damage caused by ammonia released during urease activity can, however, be a serious problem in patients with indwelling catheters and our remedies are unsatisfactory.

Catheter associated urinary tract infection and encrustation

This paper examines the relationship between urinary pH, infection and urinary catheter encrustation and discusses the current management and problems of catheter associated urinary infection and encrustation.

Catheter-associated urinary tract infections

In the past few years it has been clearly demonstrated that the concept of bacterial biofilm production permits an understanding and provides some explanation of the pathogenesis, diagnosis and treatment of catheter-associated urinary tract infections. This concept describes the colonization of catheter surfaces and the movement of bacteria against the urinary flow. It explains the antibacterial resistance of these matrix-enclosed sessile populations of bacteria. The catheter encrustation can be observed as mineralizing bacterial biofilm. The differentiation in swarming cells exposing a much higher activity of the enzyme urease is responsible for the predominant role of Proteus mirabilis in obstructing encrustations. The guidelines for the prevention of catheter-associated urinary tract infections were developed over the past decades by clinicians and are still valid. They can now be better understood taking into consideration these new theories. As overuse of urethral catheters and non-compliance of their recommended use are still apparent, educational and surveillance programmes are needed to help maintain good standards of care.

Nonsurgical management of infection-related renal calculi

Struvite calculi can be a debilitating affliction for which the cure is mainly surgical. If left untreated, infection-related calculi can cause failure to thrive, anemia, chronic renal insufficiency, renal failure and death. There has been much research aimed at non-surgical intervention and prevention of these calculi especially in this "non-invasive" era. The historic and current non-surgical treatment modalities of struvite calculi are discussed.

Microbial metal-binding mechanisms and their relation to nuclear waste disposal

The cell surface polymers of microorganisms readily bind a variety of metal ions, which enables the organisms to immobilize potentially toxic metal ions before they encounter the plasma membrane. Under appropriate chemical conditions, bound metal ions can form a variety of minerals that may be of major geological importance. Many studies have shown the occurrence of metal binding and biomineralization in nature, but detailed knowledge of the underlying mechanisms is lacking. The microbial influence of this binding may be indirect, such as physicochemical influences on the solution chemistry, Eh, and pH; or direct, when it is determined by the type of organisms present, their energy metabolism, and the structural and chemical characteristics of the cell surface and extracellular polymers. Metal binding by bacterial cell surfaces has several implications in nuclear waste disposal including adsorption of soluble radionuclides. A detailed knowledge of the chemical mechanisms of metal interactions with the microbial cell surface will enhance our understanding of the geochemical environment within a nuclear waste disposal vault.Key words: biomineralization, radionuclide immobilization, biofilm, bacterial cell surface.

Bladder instillations and bladder washouts in the management of catheterized patients

Considerable controversy exists over the instillation of solutions into the bladder of catheterized patients. The main purpose of this paper is to present existing research-based evidence on the potential advantages and disadvantages of their use to assist practitioners to clarify the issues and to make informed decisions during client care.

Analysis of bacteriuria in patients with burns

A detailed analysis of bacteriuria in 148 aged patients with burns was made for a period of 2 years (1991-92), in order to determine the incidence of the urine infections they sustained, the sources and mechanisms of the infections and the impact on the course and outcome of the primary disease. Urine infection was found in 7.6 per cent (46 patients) of all patients treated for burns during the study period; 39.1 per cent were community acquired uroinfection (CAU) and 60.9 per cent were hospital acquired (HAU). In addition there were eight patients with bacteriuria, secondary to a generalized bacterial infection (GBI), and 11 with candiduria associated with massive antibacterial therapy. Leading causes of CAU were the common uropathogens: E. coli, Citrobacter and Proteus sp.; those of HAU were multiresistant hospital strains, characteristic of the Burns Clinic: Pseud. aeruginosa, Klebsiella sp., Acinetobacter sp. and Serratia sp. This study confirmed the role of transurethral catheterizations as factors associated with the development or exacerbation of chronic uroinfections, which increased the chances of non-survival, especially in aged people with concomitant chronic urological, nephrological or other underlying diseases. The causes of death in 20 patients with HAU, CAU, GBI and candiduria were analysed. The need for strict monitoring of burned patients at risk for uroinfection development and the need to take urgent preventive measures is emphasized.

Application of 1D and 2D NMR techniques to the structure elucidation of the O-polysaccharide from Proteus mirabilis O:57

The LPS O-polysaccharide (O-PS) produced by Proteus mirabilis serotype O:57 (ATCC 49995) was shown by NMR spectroscopy and chemical analysis to be a high-molecular-weight acidic branched polymer of pentasaccharide repeating units, composed of D-glucose, D-galactose, 2-acetamido-2-deoxy-D-galactose and glycerophosphate residues (1:2:2:2:1). Application of one- and two-dimensional NMR methods allowed the complete assignment of notoriously crowded 1H and 13C spectra of the O-PS, leading to the determination of its structure. Several of the NMR techniques used were applied for the first time to the structure elucidation of polysaccharides. The resonances of galactose H5, H6 and H6' were identified by a 1D analog of 3D NOESY-TOCSY and 2D (1H,1H) triple-quantum experiments. The position and the nature of the phosphate group were determined from 2D 31P (omega 1)-half-filtered COSY and 2D 31P-relayed COSY spectra. 2D HMQC-TOCSY and 2D single-quantum proton-carbon long-range correlation techniques were used to overcome the difficulties of severe overlap and higher order effects in the 1H NMR spectrum of the O-PS. The latter technique, together with 2D NOESY, enabled us to identify the substitution positions, the anomeric configurations and the sequence of the component glycose residues in the O-PS.

Long-term studies of urease-induced crystallization in human urine

Urine samples were inoculated with viable Proteus mirabilis or purified Jack bean urease. The subsequent pH increase and crystallization were followed for 2 weeks. Particle formation was detected much earlier and at a lower pH in urines inoculated with Proteus, in which a higher end pH was also reached. The crystal configuration in bacteria and urease inoculated samples was different. Crystal aggregation was also much more pronounced in the Proteus mirabilis inoculated samples. The total precipitation was markedly increased in the Proteus mirabilis inoculated samples. The presence of live Proteus mirabilis thus has a profound influence on urease-induced crystallization in human urine. Despite the formation of rather large crystal aggregates in the Proteus-inoculated urines, no firm aggregates of a "prestone" type were observed.

Unique ability of the Proteus mirabilis capsule to enhance mineral growth in infectious urinary calculi

Struvite (MgNH4PO4.6H2O) calculi are a common complication of Proteus mirabilis urinary tract infections. Although urease is a major virulence factor in calculus formation, the polysaccharide capsule (CPS) of this organism also enhances struvite crystallization and growth in vitro (L. Clapham, R. J. C. McLean, J. C. Nickel, J. Downey, and J. W. Costerton, J. Crystal Growth 104:475-484, 1990). We obtained purified CPS, of known structure and varying anionic character, from P. mirabilis ATCC 49565 and several other organisms. Artificial urine was added to CPS, and the pH was elevated from 5.8 to 8.5 by the addition of urease or titration with 0.25 M NH4OH to induce struvite crystallization. Crystallization was measured by particle counting (Coulter counter), and the morphology (crystal habit) was examined by phase-contrast microscopy. In the presence of partially anionic P. mirabilis CPS, struvite formation occurred at a lower pH than in the absence of CPS or in the presence of other neutral, partially anionic, or anionic CPS. At pH 7.5 to 8.0, significantly more struvite crystals formed in the presence of P. mirabilis CPS than under other experimental conditions. With the exception of one polymer (curdlan) which did not bind Mg2+, enhancement of struvite formation by CPS polymers was inversely proportional to their Mg2+ binding ability. We speculate that the structure and partial anionic nature of P. mirabilis CPS enable it to enhance struvite formation by weakly concentrating Mg2+ ions during struvite crystal formation. This illustrates a new virulence aspect of bacterial CPS during infection.

Lithogenic properties of enterocystoplasty

Calculi formed in 26 of 87 patients (30%) following augmentation enterocystoplasty, of which 23 formed within the reservoir, at a mean interval of 25 months postoperatively. The calculi were composed principally of triple phosphates suggesting an important etiological role of bacteriuria and the urease reaction. Open cystolithotomy was the most successful means of removing the calculi.

Capsule structure of Proteus mirabilis (ATCC 49565)

Proteus mirabilis 2573 (ATCC 49565) produces an acidic capsular polysaccharide which was shown from glycose analysis, carboxyl reduction, methylation, periodate oxidation, and the application of one dimensional and two-dimensional high-resolution nuclear magnetic resonance techniques to be a high-molecular-weight polymer of branched trisaccharide units composed of 2-acetamido-2-deoxy-D-glucose (N-acetyl-D-glucosamine), 2-acetamido-2,6-dideoxy-L-galactose (N-acetyl-L-fucosamine), and D-glucuronic acid, having the structure: [formula: see text] P. mirabilis 2573 also produces an O:6 serotype lipopolysaccharide in which the O-chain component has the same structure as the homologous capsular polysaccharide. This is the first report of a defined capsular polysaccharide in this bacterial genus.

Bacterial colonization behaviour: a new virulence strategy in urinary infections?

The urinary bladder resists bacterial colonization and infection by a number of mechanisms, one of which involves the sloughing of colonized uroepithelial cells. Pathogens which thus become detached from bladder tissue are rapidly eliminated upon voiding of urine. During a recent study of bacterial colonization by the urinary pathogen, Proteus mirabilis, we noted that it colonized glass surfaces such that organisms became widely and evenly dispersed over the surface. In contrast, Pseudomonas fluorescens, a non-pathogen in the urinary tract, did not disperse over the surface but colonized and grew in such a manner as to form small clumps or microcolonies. Other investigators have also shown that Escherichia coli, a common urinary pathogen, initially colonizes bladders in a random, widely-dispersed fashion. We propose that successful bladder pathogens will predominantly adopt colonization behaviour that enables them to widely disperse over bladder tissue and, in so doing, avoid being cleared by the desquamation of uroepithelial cells. Colonization behaviour would therefore represent a previously uncharacterized virulence strategy.