Contribution of Proteus mirabilis urease to persistence, urolithiasis, and acute pyelonephritis in a mouse model of ascending urinary tract infection

Proteus mirabilis UreR coordinates cellular functions required for urease activity

A hallmark of Proteus mirabilis infection of the urinary tract is the formation of stones. The ability to induce urinary stone formation requires urease, a nickel metalloenzyme that hydrolyzes urea. This reaction produces ammonia as a byproduct, which can serve as a nitrogen source and weak base that raises the local pH. The resulting alkalinity induces the precipitation of ions to form stones. Transcriptional regulator UreR activates expression of urease genes in a urea-dependent manner. Thus, urease genes are highly expressed in the urinary tract where urea is abundant. Production of mature urease also requires the import of nickel into the cytoplasm and its incorporation into the urease apoenzyme. Urease accessory proteins primarily acquire nickel from one of two nickel transporters and facilitate incorporation of nickel to form mature urease. In this study, we performed a comprehensive RNA-seq to define the P. mirabilis urea-induced transcriptome as well as the UreR regulon. We identified UreR as the first defined regulator of nickel transport in P. mirabilis. We also offer evidence for the direct regulation of the Ynt nickel transporter by UreR. Using bioinformatics, we identified UreR-regulated urease loci in 15 Morganellaceae family species across three genera. Additionally, we located two mobilized UreR-regulated urease loci that also encode the ynt transporter, implying that UreR regulation of nickel transport is a conserved regulatory relationship. Our study demonstrates that UreR specifically regulates genes required to produce mature urease, an essential virulence factor for P. mirabilis uropathogenesis.

IMPORTANCE

Catheter-associated urinary tract infections (CAUTIs) account for over 40% of acute nosocomial infections in the USA and generate $340 million in healthcare costs annually. A major causative agent of CAUTIs is Proteus mirabilis, an understudied Gram-negative pathogen noted for its ability to form urinary stones via the activity of urease. Urease mutants cannot induce stones and are attenuated in a murine UTI model, indicating this enzyme is essential to P. mirabilis pathogenesis. Transcriptional regulation of urease genes by UreR is well established; here, we expand the UreR regulon to include regulation of nickel import, a function required to produce mature urease. Furthermore, we reflect on the role of urea catalysis in P. mirabilis metabolism and provide evidence for its importance.

Overview of Proteus mirabilis pathogenicity and virulence. Insights into the role of metals

Proteus mirabilis is a Gram-negative bacterium with exclusive molecular and biological features. It is a versatile pathogen acclaimed for its distinct urease production, swarming behavior, and rapid multicellular activity. Clinically, P. mirabilis is a frequent pathogen of the human urinary system where it causes urinary tract infections (UTIs) and catheter-associated urinary tract infections (CAUTIs). This review explores the epidemiology, risk factors, clinical manifestations, and treatment of P. mirabilis infections, emphasizing its association with UTIs. The bacterium's genome analysis revealed the presence of resistance genes against commonly used antibiotics, an antibiotic-resistant phenotype that poses a serious clinical challenge. Particularly, the emergence of extended-spectrum β-lactamases (ESBLs) and carbapenemases resistant P. mirabilis strains. On a molecular level, P. mirabilis possesses a wide array of virulence factors including the production of fimbriae, urease, hemolysins, metallophores, and biofilm formation. This review thoroughly tackles a substantial gap in understanding the role of metallophores in shaping the virulence factors of P. mirabilis virulence. Siderophores, iron metal chelating and transporting metallophores, particularly contribute to the complex pathogenic strategies, displaying a potential target for therapeutic intervention.

Synthesis and biological activities of alcohol extract of black cumin seeds (Bunium persicum)-based gold nanoparticles and their catalytic applications

Fast, simple, and environmentally friendly gold nanoparticles (Au-NPs) capped and stabilized with black cumin (Bunium persicum) seed alcohol extract are reported. The aqueous gold ions (Au3+) were treated with B. persicum (BP) seed extract, which resulted in a rapid color change to red, indicating the synthesis of Au-NPs. UV-Vis spectroscopy, FTIR, SEM, energy dispersive X-ray (EDX), and X-ray diffraction (XRD) techniques were used to further characterize the Au-NPs. Its stability was assessed against various pH levels and sodium chloride levels (NaCl), different salts of same concentration as well as at a range of temperature (30–100°C). The UV-Vis spectrum in the Au-NPs produced a 540 nm plasmon surface resonance, and a 25–50 nm range of particulates was shown in the SEM analysis. In addition, the FTIR spectra confirmed the inclusion in the capping and decrease of Au-NPs of amines, amide groups, and alcohols. The EDX analysis confirmed the presence of element Au. Furthermore, Au-NPs were tested for enzyme inhibition and antibacterial and antifungal activities and showed remarkable response. These findings have concluded that BP seed extract is an effective bio-reductant of gold nanoparticle synthesis, which can be further applied in different biomedical and pharmaceutical industries.

Construction and development of FimH lectin domain for rising immune response after injection by uropathogenic E. coli

Uropathogenic E. coli is one of the major agents of urinary tract infection. Today, no effective treatment or vaccine against this infection is exist. Accordingly, in the present study, a genetic constrruct for inducing of cellular immune system was designed. At first, fimH gene from E. coli 35218 was amplified using PCR. PCR product inserted into pET23a expression vector and the recombinant vector was analysed by sequencing. The vector was transformed to E. coli strain Origami and the protein was expressed under the 1 mM IPTG. FimH was purified with Ni-NTA column and the purified protein was used for immunization of BALB/c. Two weeks after the last injection, lymphocyte proliferation assay was carried out. In addition, IL-4 and IFN-γ cytokines, total antibody serum, IgG1 and IgG2a isotypes were quantified. Finally, protection ability of the vaccine in bladder and kidney infection of mice was evaluated.The results indicated that cellular immune response has a main protective role against UTI and FimH, as a vaccine candidate, significantly increase lymphocyte proliferation, IFN-γ response and total antibody amount. Immunization of mice with FimH conferred effective protection of kidney and bladder against urinary tract infection by uropathogenic E. coli (P< 0.002). It can be concluded that, the current FimH will be valuable for more trying to prepare a new vaccine against UTI.

A small-molecular inhibitor against Proteus mirabilis urease to treat catheter-associated urinary tract infections

Infection and blockage of indwelling urinary catheters is significant owing to its high incidence rate and severe medical consequences. Bacterial enzymes are employed as targets for small molecular intervention in human bacterial infections. Urease is a metalloenzyme known to play a crucial role in the pathogenesis and virulence of catheter-associated Proteus mirabilis infection. Targeting urease as a therapeutic candidate facilitates the disarming of bacterial virulence without affecting bacterial fitness, thereby limiting the selective pressure placed on the invading population and lowering the rate at which it will acquire resistance. We describe the design, synthesis, and in vitro evaluation of the small molecular enzyme inhibitor 2-mercaptoacetamide (2-MA), which can prevent encrustation and blockage of urinary catheters in a physiologically representative in vitro model of the catheterized urinary tract. 2-MA is a structural analogue of urea, showing promising competitive activity against urease. In silico docking experiments demonstrated 2-MA's competitive inhibition, whilst further quantum level modelling suggests two possible binding mechanisms.

Neutrophil-Macrophage Imbalance Drives the Development of Renal Scarring during Experimental Pyelonephritis

BACKGROUND

In children, the acute pyelonephritis that can result from urinary tract infections (UTIs), which commonly ascend from the bladder to the kidney, is a growing concern because it poses a risk of renal scarring and irreversible loss of kidney function. To date, the cellular mechanisms underlying acute pyelonephritis-driven renal scarring remain unknown.

METHODS

We used a preclinical model of uropathogenic Escherichia coli-induced acute pyelonephritis to determine the contribution of neutrophils and monocytes to resolution of the condition and the subsequent development of kidney fibrosis. We used cell-specific monoclonal antibodies to eliminate neutrophils, monocytes, or both. Bacterial ascent and the cell dynamics of phagocytic cells were assessed by biophotonic imaging and flow cytometry, respectively. We used quantitative RT-PCR and histopathologic analyses to evaluate inflammation and renal scarring.

RESULTS

We found that neutrophils are critical to control bacterial ascent, which is in line with previous studies suggesting a protective role for neutrophils during a UTI, whereas monocyte-derived macrophages orchestrate a strong, but ineffective, inflammatory response against uropathogenic, E. coli-induced, acute pyelonephritis. Experimental neutropenia during acute pyelonephritis resulted in a compensatory increase in the number of monocytes and heightened macrophage-dependent inflammation in the kidney. Exacerbated macrophage-mediated inflammatory responses promoted renal scarring and compromised renal function, as indicated by elevated serum creatinine, BUN, and potassium.

CONCLUSIONS

These findings reveal a previously unappreciated outcome for neutrophil-macrophage imbalance in promoting host susceptibility to acute pyelonephritis and the development of permanent renal damage. This suggests targeting dysregulated macrophage responses might be a therapeutic tool to prevent renal scarring during acute pyelonephritis.

Proteomic analysis deciphers the multi-targeting antivirulence activity of tannic acid in modulating the expression of MrpA, FlhD, UreR, HpmA and Nrp system in Proteus mirabilis

In the present study, the multi-targeting antivirulence activity of tannic acid (TA) was explored against Proteus mirabilis through MS-based proteomic approach. The in vitro biofilm biomass quantification assay and microscopic analysis demonstrated the antibiofilm activity of TA against P. mirabilis in which, minimum biofilm inhibitory concentration (MBIC) of TA was found to be 200 μg/mL concentration. Moreover, the nanoscale liquid chromatography coupled to tandem mass spectrometry (nano LC-MS/MS) analysis revealed that TA (at MBIC) differentially regulated the proteins involved in fimbrial adhesion, flagellar motility, iron acquisition, Fe-S cluster assembly, heat shock response, virulence enzymes, and toxin secretion. Further, the transcriptomic analysis validated the outcomes of proteomic analysis in which, the expression level of virulence genes responsible for MR/P fimbrial adhesion (mrpA), flagellar transcriptional activation (flhD), biosynthesis of urease (ureR), hemolysin (hpmA), non-ribosomal peptide siderophore system (Nrp), oxidative stress responsible enzymes and fitness factors proteins were down-regulated in TA exposed P. mirabilis. These observations were also in correspondence with the in vitro bioassays. Thus, this study reports the feasibility of TA to act as a promising therapeutic agent against multifactorial P. mirabilis infections.

Molecular Characterization of the Purine Degradation Pathway Genes ALA1 and URE1 of the Maize Anthracnose Fungus Colletotrichum graminicola Identified Urease as a Novel Target for Plant Disease Control

Fungal pathogenicity is governed by environmental factors, with nitrogen playing a key role in triggering pathogenic development. Spores germinating on the plant cuticle are exposed to a nitrogen-free environment, and reprograming of nitrogen metabolism is required for bridging the time needed to gain access to the nitrogen sources of the host. Although degradation of endogenous purine bases efficiently generates ammonium and may allow the fungus to bridge the preinvasion nitrogen gap, the roles of the purine degradation pathway and of the key genes encoding allantoicase and urease are largely unknown in plant pathogenic fungi. To investigate the roles of the allantoicase and urease genes ALA1 and URE1 of the maize anthracnose fungus Colletotrichum graminicola in pathogenic development, we generated ALA1:eGFP and URE1:eGFP fusion strains as well as allantoicase- and urease-deficient mutants. Virulence assays, live cell, and differential interference contrast imaging, chemical complementation and employment of a urease inhibitor showed that the purine degradation genes ALA1 and URE1 are required for bridging nitrogen deficiency at early phases of the infection process and for full virulence. Application of the urease inhibitor acetohydroxamic acid did not only protect maize from C. graminicola infection, but also interfered with the infection process of the wheat powdery mildew fungus Blumeria graminis f. sp. tritici, the maize and broad bean rusts Puccinia sorghi and Uromyces viciae-fabae, and the potato late blight pathogen Phytophthora infestans. Our data strongly suggest that inhibition of the purine degradation pathway might represent a novel approach to control plant pathogenic fungi and oomycetes.

Attenuation of Proteus mirabilis colonization and swarming motility on indwelling urinary catheter by antibiofilm impregnation: An in vitro study

Proteus mirabilis is one of the important etiologic agents of urinary tract infections (UTI), which complicates the long-term urinary catheterization process in clinical settings. Owing to its crystalline biofilm forming ability and flagellar motility, elimination of P. mirabilis from urinary system becomes very difficult. Thus, the present study is focused to prepare antibiofilm-impregnated Silicone Foley Catheter (SFC) to prevent P. mirabilis instigated UTIs. Through solvent swelling method, the antibiofilm compounds such as linalool (LIN) and 2-hydroxy-4-methoxy benzaldehyde (HMB) were successfully infused into SFCs. Surface topography was studied using AFM analysis, which unveiled the unmodified surface roughness of normal and antibiofilm-impregnated SFCs. In addition, UV-spectrometric and FT-IR analyses revealed good impregnation efficacy and prolonged stability of antibiofilm compounds. Further, in vitro biofilm biomass quantification assay exhibited a maximum of 87 % and 84 % crystalline biofilm inhibition in LIN (350 μg/cm³) and HMB (120 μg/cm³) impregnated SFCs, respectively against P. mirabilis in artificial urine medium. Also, the LIN & HMB-impregnated SFCs demonstrated long-term crystalline biofilm inhibitory activity for more than 30 days, which is ascribed to the sustained release of the compounds. Furthermore, the results of swarming motility analysis revealed the efficacy of antibiofilm-impregnated catheters to mitigate the migration of pathogens over them. Thus, antibiofilm-impregnated catheter is proposed to act as a suitable strategy for reducing P. mirabilis infections and associated complications in long-term urinary catheter users.

Ynt is the primary nickel import system used by Proteus mirabilis and specifically contributes to fitness by supplying nickel for urease activity

Proteus mirabilis is a Gram-negative uropathogen and frequent cause of catheter-associated urinary tract infection (CAUTI). One important virulence factor is its urease enzyme, which requires nickel to be catalytically active. It is, therefore, hypothesized that nickel import is critical for P. mirabilis urease activity and pathogenesis during infection. P. mirabilis strain HI4320 encodes two putative nickel import systems, designated Nik and Ynt. By disrupting the substrate-binding proteins from each import system (nikA and yntA), we show that Ynt is the primary nickel importer, while Nik only compensates for loss of Ynt at high nickel concentrations. We further demonstrate that these are the only binding proteins capable of importing nickel for incorporation into the urease enzyme. Loss of either nickel-binding protein results in a significant fitness defect in a murine model of CAUTI, but YntA is more crucial as the yntA mutant was significantly outcompeted by the nikA mutant. Furthermore, despite the importance of nickel transport for hydrogenase activity, the sole contribution of yntA and nikA to virulence is due to their role in urease activity, as neither mutant exhibited a fitness defect when disrupted in a urease-negative background.

Inhibition of urease activity in the urinary tract pathogens Staphylococcus saprophyticus and Proteus mirabilis by dimethylsulfoxide (DMSO)

AIMS

Urease is a virulence factor for the urinary tract pathogens Staphylococcus saprophyticus and Proteus mirabilis. Dimethylsulfoxide (DMSO) is structurally similar to urea, used as a solvent for urease inhibitors, and an effective treatment for interstitial cystitis/bladder pain syndrome (IC/BPS). The aims of this study were to test DMSO as a urease inhibitor and determine its physiological effects on S. saprophyticus and P. mirabilis.

METHODS AND RESULTS

Urease activity in extracts and whole cells was measured by the formation of ammonium ions. Urease was highly sensitive to noncompetitive inhibition by DMSO (K_i about 6 mmol l^-1 ). DMSO inhibited urease activity in whole cells, limited bacterial growth in media containing urea, and slowed the increase in pH which occurred in artificial urine medium.

CONCLUSIONS

DMSO should be used with caution as a solvent when testing plant extracts or other potential urease inhibitors. Because it can inhibit bacterial growth and delay an increase in pH, it may be an effective treatment for urinary tract infections.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first detailed study of the inhibition of urease by DMSO. Dimethylsulfoxide may be used to treat urinary tract infections that are resistant to antibiotics or herbal remedies.

Evaluation of hematogenous spread and ascending infection in the pathogenesis of acute pyelonephritis due to group B streptococcus in mice

Group B streptococcus (GBS) causes pyelonephritis in adults but the mechanisms of infection by which GBS infects the kidneys in vivo are unknown. We investigated GBS infection of the kidneys in mice following experimental challenge via the hematogenous route (transient bacteremia model) or transurethral route (bladder infection and cystitis model). Adult female mice were examined for bacterial dissemination to the kidneys and other organ systems at 24-72 h and tissue samples were assessed for histopathological changes. Comparisons included analysis of different challenge inoculum doses ranging between 10⁷-10⁹ CFU and investigation of several GBS serotypes, including representative strains of serotype V (NEM316), III (BM110, 874391) and Ia (807). Mice with transient, low-level GBS bacteremia routinely developed acute pyelonephritis secondary to high-level kidney infection; infection progressed with high GBS burdens that were sustained in the tissue for days in contrast to bacterial clearance in other organs, including spleen, liver and heart. The histopathological changes of acute pyelonephritis due to GBS were characterized using hematoxylin and eosin, and stains for bacteria, neutrophils, macrophages, mast cells and T lymphocytes; this revealed recruitment of a mixed inflammatory cell population that infiltrated the renal medulla of infected mice in focal areas of discrete micro-abscesses. In contrast, bladder infection leading to cystitis in mice did not result in ascending spread of GBS to the kidneys. We conclude that transient bacteremia, rather than preceding infection of the lower urinary tract, is the predominant condition that leads to GBS kidney infection and subsequent development of acute pyelonephritis.

Quantification of Urease Activity

Urease is one of the most distinctive virulence factors of Proteus mirabilis pathogenesis. Urease activity correlates with many landmark side effects of P. mirabilis catheter-associated urinary tract infections, such as urolithiasis and bacteremia. Here we describe two simple and inexpensive colorimetric methods for quantifying urease activity in single species cultures as well as cocultures.

Role of Nickel in Microbial Pathogenesis

Nickel is an essential cofactor for some pathogen virulence factors. Due to its low availability in hosts, pathogens must efficiently transport the metal and then balance its ready intracellular availability for enzyme maturation with metal toxicity concerns. The most notable virulence-associated components are the Ni-enzymes hydrogenase and urease. Both enzymes, along with their associated nickel transporters, storage reservoirs, and maturation enzymes have been best-studied in the gastric pathogen Helicobacter pylori, a bacterium which depends heavily on nickel. Molecular hydrogen utilization is associated with efficient host colonization by the Helicobacters, which include both gastric and liver pathogens. Translocation of a H. pylori carcinogenic toxin into host epithelial cells is powered by H2 use. The multiple [NiFe] hydrogenases of Salmonella enterica Typhimurium are important in host colonization, while ureases play important roles in both prokaryotic (Proteus mirabilis and Staphylococcus spp.) and eukaryotic (Cryptoccoccus genus) pathogens associated with urinary tract infections. Other Ni-requiring enzymes, such as Ni-acireductone dioxygenase (ARD), Ni-superoxide dismutase (SOD), and Ni-glyoxalase I (GloI) play important metabolic or detoxifying roles in other pathogens. Nickel-requiring enzymes are likely important for virulence of at least 40 prokaryotic and nine eukaryotic pathogenic species, as described herein. The potential for pathogenic roles of many new Ni-binding components exists, based on recent experimental data and on the key roles that Ni enzymes play in a diverse array of pathogens.

Defining Dysbiosis in Patients with Urolithiasis

The prevalence of urinary stone disease (USD) is rapidly rising. However, the factors driving this increase are unknown. Recent microbiome studies suggest that dysbiosis may in part contribute to the increasing prevalence. The objective of the current study was to determine the nature and location of dysbiosis associated with USD. We conducted microbiome analysis from the gastrointestinal and urinary tracts, along with a metabolomic analysis of the urinary metabolome, from subjects with an active episode of USD or no history of the disease. Higher rates of antibiotic use among USD patients along with integrated microbiome and metabolomic results support the hypothesis that USD is associated with an antibiotic-driven shift in the microbiome from one that protects against USD to one that promotes the disease. Specifically, our study implicates urinary tract Lactobacillus and Enterobacteriaceae in protective and pathogenic roles for USD, respectively, which conventional, culture-based methods of bacterial analysis from urine and kidney stones would not necessarily detect. Results suggest that antibiotics produce a long-term shift in the microbiome that may increase the risk for USD, with the urinary tract microbiome holding more relevance for USD than the gut microbiome.

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.

F. A review on the development of urease inhibitors as antimicrobial agents against pathogenic bacteria

Ureases are enzymes that hydrolyze urea into ammonium and carbon dioxide. They have received considerable attention due to their impacts on living organism health, since the urease activity in microorganisms, particularly in bacteria, are potential causes and/or factors contributing to the persistence of some pathogen infections. This review compiles examples of the most potent antiurease organic substances. Emphasis was given to systematic screening studies on the inhibitory activity of rationally designed series of compounds with the corresponding SAR considerations. Ureases of Canavalia ensiformis, the usual model in antiureolytic studies, are emphasized. Although the active site of this class of hydrolases is conserved among bacteria and vegetal ureases, the same is not observerd for allosteric site. Therefore, inhibitors acting by participating in interactions with the allosteric site are more susceptible to a potential lack of association among their inhibitory profile for different ureases. The information about the inhibitory activity of different classes of compounds can be usefull to guide the development of new urease inhibitors that may be used in future in small molecular therapy against pathogenic bacteria.

Microbial Load in Septic and Aseptic Procedure Rooms

BACKGROUND

Highly effective measures to prevent surgical wound infections have been established over the last two decades. We studied whether the strict separation of septic and aseptic procedure rooms is still necessary.

METHODS

In an exploratory, prospective observational study, the microbial concentration in an operating room without a room ventilating system (RVS) was analyzed during 16 septic and 14 aseptic operations with the aid of an air sampler (50 cm and 1 m from the operative field) and sedimentation plates (1 m from the operative field, and contact culture on the walls). The means and standard deviations of the microbial loads were compared with the aid of GEE models (generalized estimation equations).

RESULTS

In the comparison of septic and aseptic operations, no relevant differences were found with respect to the overall microbial concentration in the room air (401.7 ± 176.3 versus 388.2 ± 178.3 CFU/m3; p = 0.692 [CFU, colony-forming units]) or sedimentation 1 m from the operative field (45.3 ± 22.0 versus 48.7 ± 18.5 CFU/m2/min; p = 0.603) and on the walls (35.7 ± 43.7 versus 29.0 ± 49.4 CFU/m2/min; p = 0.685). The only relevant differences between the microbial spectra associated with the two types of procedure were a small amount of sedimentation of Escherichia coli and Enterococcus faecalis in septic operations, and of staphylococcus aureus and pseudomonas stutzeri in aseptic operations, up to 30 minutes after the end of the procedure.

CONCLUSION

These data do not suggest that septic and aseptic procedure rooms need to be separated. In interpreting the findings, one should recall that the study was not planned as an equivalence or non-inferiority study. Wherever patient safety is concerned, high-level safety concepts should only be demoted to lower levels if new and convincing evidence becomes available.

Limited effectiveness of over-the-counter plant preparations used for the treatment of urinary tract infections as inhibitors of the urease activity from Staphylococcus saprophyticus

AIMS

Urease is a key virulence factor for the Gram-positive urinary tract pathogen Staphylococcus saprophyticus and a potential target for antimicrobial therapy. The enzyme from S. saprophyticus is unusual in that it does not contain cysteine at the active site. The aims of this study were to test 14 over-the-counter plant preparations as inhibitors of this urease and to determine whether they can prevent the increase in pH that normally occurs in bacterial cultures containing urea.

METHODS AND RESULTS

Urease activity was measured colorimetrically by the formation of ammonium ions. The green tea and Uva-Ursi preparations reduced urease activity in a soluble extract of S. saprophyticus by more than 75%. Two herbal mixtures were weakly inhibitory and reduced activity by about 25%, but the other products had little or no effect. The green tea and Uva-Ursi extracts also inhibited urease activity in whole cells by more than 75%. One of the herbal products (WishGarden UTI) showed some inhibition of urease activity but the other (UTI Clear) did not. The green tea and Uva-Ursi preparations prevented the increase in pH that normally occurs when S. saprophyticus is grown in an artificial urine medium, but this was due primarily to bacterial death. The WishGarden UTI preparation could partially delay the pH increase while allowing some cells to remain viable.

CONCLUSION

These results indicate that only a few of the commercially available over-the-counter plant preparations commonly used for the treatment of urinary tract infections (UTIs) can inhibit the urease activity from S. saprophyticus.

SIGNIFICANCE AND IMPACT OF THE STUDY

While over-the-counter plant preparations may be considered an alternative to traditional antibiotics for the treatment of UTIs, they should be used with caution and a product should be matched to the properties of the virulence factors of the bacterial pathogen involved.

Genome-wide transposon mutagenesis of Proteus mirabilis: Essential genes, fitness factors for catheter-associated urinary tract infection, and the impact of polymicrobial infection on fitness requirements

The Gram-negative bacterium Proteus mirabilis is a leading cause of catheter-associated urinary tract infections (CAUTIs), which are often polymicrobial. Numerous prior studies have uncovered virulence factors for P. mirabilis pathogenicity in a murine model of ascending UTI, but little is known concerning pathogenesis during CAUTI or polymicrobial infection. In this study, we utilized five pools of 10,000 transposon mutants each and transposon insertion-site sequencing (Tn-Seq) to identify the full arsenal of P. mirabilis HI4320 fitness factors for single-species versus polymicrobial CAUTI with Providencia stuartii BE2467. 436 genes in the input pools lacked transposon insertions and were therefore concluded to be essential for P. mirabilis growth in rich medium. 629 genes were identified as P. mirabilis fitness factors during single-species CAUTI. Tn-Seq from coinfection with P. stuartii revealed 217/629 (35%) of the same genes as identified by single-species Tn-Seq, and 1353 additional factors that specifically contribute to colonization during coinfection. Mutants were constructed in eight genes of interest to validate the initial screen: 7/8 (88%) mutants exhibited the expected phenotypes for single-species CAUTI, and 3/3 (100%) validated the expected phenotypes for polymicrobial CAUTI. This approach provided validation of numerous previously described P. mirabilis fitness determinants from an ascending model of UTI, the discovery of novel fitness determinants specifically for CAUTI, and a stringent assessment of how polymicrobial infection influences fitness requirements. For instance, we describe a requirement for branched-chain amino acid biosynthesis by P. mirabilis during coinfection due to high-affinity import of leucine by P. stuartii. Further investigation of genes and pathways that provide a competitive advantage during both single-species and polymicrobial CAUTI will likely provide robust targets for therapeutic intervention to reduce P. mirabilis CAUTI incidence and severity.

Proteus mirabilis is a common cause of single-species and polymicrobial catheter-associated urinary tract infections (CAUTIs). Prior studies have uncovered P. mirabilis virulence factors for single-species ascending UTI, but little is known concerning pathogenesis during CAUTI or polymicrobial infection. Using transposon insertion-site sequencing (Tn-Seq), we performed a global assessment of P. mirabilis fitness factors for CAUTI while simultaneously determining how coinfection with another CAUTI pathogen, Providencia stuartii, alters P. mirabilis fitness requirements. This approach provides six important contributions to the field: 1) the first global estimation of P. mirabilis genes essential for growth, 2) validation of a role for known P. mirabilis fitness factors during CAUTI, 3) identification of novel fitness factors, 4) identification of core fitness factors for both single-species and polymicrobial CAUTI, 5) identification of single-species fitness factors that are complemented during polymicrobial infection, and 6) identification of factors that only provide a competitive advantage during polymicrobial infection. We further demonstrate that the CAUTI model can be used to examine the interplay between fitness requirements of both species during coinfection. Investigation of fitness requirements for other pathogens during single-species and polymicrobial CAUTI will elucidate complex interactions that contribute to disease severity and uncover conserved targets for therapeutic intervention.

From Catheter to Kidney Stone: The Uropathogenic Lifestyle of Proteus mirabilis

Proteus mirabilis is a model organism for urease-producing uropathogens. These diverse bacteria cause infection stones in the urinary tract and form crystalline biofilms on indwelling urinary catheters, frequently leading to polymicrobial infection. Recent work has elucidated how P. mirabilis causes all of these disease states. Particularly exciting is the discovery that this bacterium forms large clusters in the bladder lumen that are sites for stone formation. These clusters, and other steps of infection, require two virulence factors in particular: urease and MR/P fimbriae. Highlighting the importance of MR/P fimbriae is the cotranscribed regulator, MrpJ, which globally controls virulence. Overall, P. mirabilis exhibits an extraordinary lifestyle, and further probing will answer exciting basic microbiological and clinically relevant questions.

Proteus mirabilis and Urinary Tract Infections

Proteus mirabilis is a Gram-negative bacterium and is well known for its ability to robustly swarm across surfaces in a striking bulls'-eye pattern. Clinically, this organism is most frequently a pathogen of the urinary tract, particularly in patients undergoing long-term catheterization. This review covers P. mirabilis with a focus on urinary tract infections (UTI), including disease models, vaccine development efforts, and clinical perspectives. Flagella-mediated motility, both swimming and swarming, is a central facet of this organism. The regulation of this complex process and its contribution to virulence is discussed, along with the type VI-secretion system-dependent intra-strain competition, which occurs during swarming. P. mirabilis uses a diverse set of virulence factors to access and colonize the host urinary tract, including urease and stone formation, fimbriae and other adhesins, iron and zinc acquisition, proteases and toxins, biofilm formation, and regulation of pathogenesis. While significant advances in this field have been made, challenges remain to combatting complicated UTI and deciphering P. mirabilis pathogenesis.

Role of DAF-21protein in Caenorhabditis elegans immunity against Proteus mirabilis infection

Caenorhabditis elegans is emerging as one of the handy model for proteome related studies due to its simplest system biology. The present study, deals with changes in protein expression in C. elegans infected with Proteus mirabilis. Proteins were separated using two-dimensional differential gel electrophoresis (2D-DIGE) and identified using MALDI-TOF. Twelve distinctly regulated proteins identified in the infected worms, included heat shock proteins involved stress pathway (HSP-1 and HSP-6), proteins involved in immune response pathway (DAF-21), enzymes involved in normal cellular process (Eukaryotic translation Elongation Factor, actin family member, S-adenosyl homocysteine hydrolase ortholog, glutamate dehydrogenase and Vacuolar H ATPase family member) and few least characterized proteins (H28O16.1 and H08J11.2). The regulation of selected players at the transcriptional level during Proteus mirabilis infection was analyzed using qPCR. Physiological experiments revealed the ability of P. mirabilis to kill daf-21 mutant C. elegans significantly compared with the wild type. This is the first report studying proteome changes in C. elegans and exploring the involvement of MAP Kinase pathway during P. mirabilis infection.

BIOLOGICAL SIGNIFICANCE

This is the first report studying proteome changes in C. elegans during P. mirabilis infection. The present study explores the role and contribution of MAP Kinase pathway and its regulator protein DAF-21 involvement in the immunity against opportunistic pathogen P. mirabilis infection. Manipulation of this DAF-21 protein in host, may pave the way for new drug development or disease control strategy during opportunistic pathogen infections.

Proteus mirabilis fimbriae- and urease-dependent clusters assemble in an extracellular niche to initiate bladder stone formation

The catheter-associated uropathogenProteus mirabilisfrequently causes urinary stones, but little has been known about the initial stages of bladder colonization and stone formation. We found thatP. mirabilisrapidly invades the bladder urothelium, but generally fails to establish an intracellular niche. Instead, it forms extracellular clusters in the bladder lumen, which form foci of mineral deposition consistent with development of urinary stones. These clusters elicit a robust neutrophil response, and we present evidence of neutrophil extracellular trap generation during experimental urinary tract infection. We identified two virulence factors required for cluster development: urease, which is required for urolithiasis, and mannose-resistantProteus-like fimbriae. The extracellular cluster formation byP. mirabilisstands in direct contrast to uropathogenicEscherichia coli, which readily formed intracellular bacterial communities but not luminal clusters or urinary stones. We propose that extracellular clusters are a key mechanism ofP. mirabilissurvival and virulence in the bladder.

Back to the metal age: battle for metals at the host-pathogen interface during urinary tract infection

Urinary tract infection (UTI) represents one of the most common bacterial infections in humans and uropathogenic E. coli (UPEC) is the major causative agent of UTI in people. Research on UPEC and other bacterial pathogens causing UTI has now identified the critical role of metal transport systems in the pathogenesis of UTI. Here we review the major effectors of metal transport in bacteria and host proteins that impair metal acquisition by bacterial pathogens. In particular, we describe the studies that identified iron, zinc and nickel import and copper export as key virulence and fitness determinants during UTI. Various metal transport systems and mechanisms that govern the expression of metal transport systems are also presented here. Specific examples from UPEC and other uropathogens, when available, are presented to depict the battle for metals at the host-pathogen interface during UTI.

Struvite Urolithiasis in Long-Evans Rats

Struvite urinary calculi, which are composed of magnesium, ammonium, and phosphate, can cause complications including sepsis and renal failure. Struvite calculi were identified within the urinary bladder and renal pelvis of 2 Long-Evans rats that died within days after arrival from a commercial vendor. The remaining rats in the shipment were screened by physical examination, radiography, and ultrasonography, revealing an additional 2 animals that were clinically affected. These rats were euthanized, necropsied, and yielded similar findings to those from the first 2 rats. In addition, urine samples had an alkaline pH and contained numerous bacteria (predominantly Proteus mirabilis), leukocytes, and crystals. All calculi were composed completely of struvite. Another 7 rats in the shipment had alkaline urine with the presence of blood cells; 6 of these rats also had abundant struvite crystals, and P. mirabilis was cultured from the urine of 3 rats. Further investigation by the vendor identified 2 of 100 rats with struvite calculi from the same colony. Although no specific cause could be implicated, the fact that all the affected rats came from the same breeding area suggests a genetic or environmental triggering event; a contribution due to diet cannot be ruled out. Our findings suggest that the affected rats had metabolic disturbances coupled with bacterial infection that predisposed them to develop struvite calculi. During sudden increases of struvite urinary calculi cases in rats, urine cultures followed by appropriate surgical intervention and antibiotic therapy is warranted. Additional factors, including diet, merit attention as well.

Urinary tract infection of mice to model human disease: Practicalities, implications and limitations

Urinary tract infections (UTIs) are among the most common bacterial infections in humans. Murine models of human UTI are vital experimental tools that have helped to elucidate UTI pathogenesis and advance knowledge of potential treatment and infection prevention strategies. Fundamentally, several variables are inherent in different murine models, and understanding the limitations of these variables provides an opportunity to understand how models may be best applied to research aimed at mimicking human disease. In this review, we discuss variables inherent in murine UTI model studies and how these affect model usage, data analysis and data interpretation. We examine recent studies that have elucidated UTI host-pathogen interactions from the perspective of gene expression, and review new studies of biofilm and UTI preventative approaches. We also consider potential standards for variables inherent in murine UTI models and discuss how these might expand the utility of models for mimicking human disease and uncovering new aspects of pathogenesis.

Host-specific induction of Escherichia coli fitness genes during human urinary tract infection

Uropathogenic Escherichia coli (UPEC) is the predominant etiological agent of uncomplicated urinary tract infection (UTI), manifested by inflammation of the urinary bladder, in humans and is a major global public health concern. Molecular pathogenesis of UPEC has been primarily examined using murine models of UTI. Translational research to develop novel therapeutics against this major pathogen, which is becoming increasingly antibiotic resistant, requires a thorough understanding of mechanisms involved in pathogenesis during human UTIs. Total RNA-sequencing (RNA-seq) and comparative transcriptional analysis of UTI samples to the UPEC isolates cultured in human urine and laboratory medium were used to identify novel fitness genes that were specifically expressed during human infection. Evidence for UPEC genes involved in ion transport, including copper efflux, nickel and potassium import systems, as key fitness factors in uropathogenesis were generated using an experimental model of UTI. Translational application of this study was investigated by targeting Cus, a bacterial copper efflux system. Copper supplementation in drinking water reduces E. coli colonization in the urinary bladder of mice. Additionally, our results suggest that anaerobic processes in UPEC are involved in promoting fitness during UTI in humans. In summary, RNA-seq was used to establish the transcriptional signature in UPEC during naturally occurring, community acquired UTI in women and multiple novel fitness genes used by UPEC during human infection were identified. The repertoire of UPEC genes involved in UTI presented here will facilitate further translational studies to develop innovative strategies against UTI caused by UPEC.

Effect of ceftriaxone on the outcome of murine pyelonephritis caused by extended-spectrum-β-lactamase-producing Escherichia coli

Urinary tract infections (UTIs) due to extended-spectrum-β-lactamase (ESBL)-producing Enterobacteriaceae in children are becoming more frequent, and they are commonly treated initially with a second- or third-generation cephalosporin. We developed a murine model of ascending UTI caused by ESBL-producing Escherichia coli. Using this model, we investigated the renal bacterial burden, interleukin-6 (IL-6) expression, and histopathological alterations caused by ESBL- and non-ESBL-producing bacteria after 1, 2, or 6 days with or without ceftriaxone therapy. The renal bacterial burden, IL-6 concentration, and histological inflammatory lesions were not significantly different between mice infected with ESBL- and non-ESBL-producing bacteria without treatment at any of the time points examined. Following ceftriaxone administration, the bacterial burden was eliminated in the kidneys of mice infected with ESBL- and non-ESBL-producing bacteria on the 6th postinfection day. The histological analysis demonstrated that among mice treated with ceftriaxone, those infected with ESBL-producing bacteria had more profound renal alterations than those infected with non-ESBL-producing bacteria on the 6th day (P < 0.001). In comparison, microbiological outcomes did not differ significantly between mice infected with ESBL- and non-ESBL-producing bacteria at any of the time points examined. The effectiveness of ceftriaxone in mice with UTIs due to ESBL-producing E. coli may have therapeutic implications; it is, however, hampered by limited activity on the histopathological lesions, a finding that needs further investigation.

Anti-Adhesion Activity of A2-type Proanthocyanidins (a Cranberry Major Component) on Uropathogenic E. coli and P. mirabilis Strains

Urinary tract infections (UTIs) are relatively common in women and may be classified as uncomplicated or complicated, depending upon the urinary tract anatomy and physiology. Acute uncomplicated cystitis (AUC) occurs when urinary pathogens from the bowel or vagina colonize the periurethral mucosa and reach the bladder. The vast majority of episodes in healthy women involving the same bacterial strain that caused the initial infection are thought to be reinfections. About 90% of AUC are caused by uropathogenic Escherichia coli (UPEC), but Proteus mirabilis also plays an important role. Several studies support the importance of cranberry (Vaccinium macrocarpon) proanthocyanidins in preventing adhesion of P-fimbriated UPEC to uroepithelial cells. In this study, we evaluated the in vitro anti-adhesion activity of A2-linked proanthocyanidins from cranberry on a UPEC and Proteus mirabilis strains and their possible influence on urease activity of the latter. A significant reduction of UPEC adhesion (up to 75%) on the HT1376 cell line was observed vs. control. For the strains of P. mirabilis there was also a reduction of adhesion (up to 75%) compared to controls, as well as a reduction in motility and urease activity. These results suggest that A2-type cranberry proanthocyanidins could aid in maintaining urinary tract health.

Increased incidence of urolithiasis and bacteremia during Proteus mirabilis and Providencia stuartii coinfection due to synergistic induction of urease activity

BACKGROUND

Catheter-associated urinary tract infections (CaUTIs) are the most common hospital-acquired infections worldwide and are frequently polymicrobial. The urease-positive species Proteus mirabilis and Providencia stuartii are two of the leading causes of CaUTIs and commonly co-colonize catheters. These species can also cause urolithiasis and bacteremia. However, the impact of coinfection on these complications has never been addressed experimentally.

METHODS

A mouse model of ascending UTI was utilized to determine the impact of coinfection on colonization, urolithiasis, and bacteremia. Mice were infected with P. mirabilis or a urease mutant, P. stuartii, or a combination of these organisms. In vitro experiments were conducted to assess growth dynamics and impact of co-culture on urease activity.

RESULTS

Coinfection resulted in a bacterial load similar to monospecies infection but with increased incidence of urolithiasis and bacteremia. These complications were urease-dependent as they were not observed during coinfection with a P. mirabilis urease mutant. Furthermore, total urease activity was increased during co-culture.

CONCLUSIONS

We conclude that P. mirabilis and P. stuartii coinfection promotes urolithiasis and bacteremia in a urease-dependent manner, at least in part through synergistic induction of urease activity. These data provide a possible explanation for the high incidence of bacteremia resulting from polymicrobial CaUTI.

Bacterial urease and its role in long-lasting human diseases

Urease is a virulence factor found in various pathogenic bacteria. It is essential in colonization of a host organism and in maintenance of bacterial cells in tissues. Due to its enzymatic activity, urease has a toxic effect on human cells. The presence of ureolytic activity is an important marker of a number of bacterial infections. Urease is also an immunogenic protein and is recognized by antibodies present in human sera. The presence of such antibodies is connected with progress of several long-lasting diseases, like rheumatoid arthritis, atherosclerosis or urinary tract infections. In bacterial ureases, motives with a sequence and/or structure similar to human proteins may occur. This phenomenon, known as molecular mimicry, leads to the appearance of autoantibodies, which take part in host molecules destruction. Detection of antibodies-binding motives (epitopes) in bacterial proteins is a complex process. However, organic chemistry tools, such as synthetic peptide libraries, are helpful in both, epitope mapping as well as in serologic investigations.

In this review, we present a synthetic report on a molecular organization of bacterial ureases - genetic as well as structural. We characterize methods used in detecting urease and ureolytic activity, including techniques applied in disease diagnostic processes and in chemical synthesis of urease epitopes. The review also provides a summary of knowledge about a toxic effect of bacterial ureases on human body and about occurrence of anti-urease antibodies in long-lasting diseases.

Enhanced susceptibility to urinary tract infection in the spinal cord-injured host with neurogenic bladder

Neurogenic bladder predisposes to recurrent urinary tract infections (UTI) and renal failure, and susceptibility is commonly ascribed to urinary stasis from elevated residual urine volumes. Escherichia coli UTI was modeled in the spinal cord-injured (SCI) rat with the hypothesis that SCI animals would require fewer bacteria to establish infection, have an exaggerated inflammatory response, and have delayed clearance of infection compared to normal-voiding controls. T10 SCI rats and controls had median infectious doses (ID50) of 10(2) and 10(5) CFU, respectively. Mean residual volumes in the SCI animals did not correlate with susceptibility to initiation of UTI or outcome. In the acute infection, control and SCI rats developed acute cystitis and pyelitis without acute differences in histopathological scores of inflammation. However, in vivo imaging of infected animals revealed persistently higher levels of bacteria in the SCI urine and bladders than were seen for controls over 2 weeks. Likewise, at 2 weeks, acute and chronic inflammatory infiltrates persisted in the bladders and kidneys of SCI rats, whereas inflammation largely resolved within the controls. Together these data demonstrate that SCI rats exhibit delayed clearance of infection and exaggerated inflammatory responses in bladders and kidneys; however, the severity of residual volumes does not predict increased susceptibility to UTI. These studies suggest that host-dependent mechanisms that are discrete from alterations in bladder physiology influence UTI susceptibility with the SCI-neurogenic bladder. This model will allow elucidation of SCI-neurogenic bladder-mediated changes in host response that yield UTI susceptibility and may lead to new preventative and therapeutic options.

Cranberry impairs selected behaviors essential for virulence in Proteus mirabilis HI4320

Proteus mirabilis is an etiological agent of complicated urinary tract infections. North American cranberries (Vaccinium macrocarpon) have long been considered to have protective properties against urinary tract infections. This work reports the effects of cranberry powder (CP) on the motility of P. mirabilis HI4320 and its expression of flaA, flhD, and ureD. Our results show that swimming and swarming motilities and swarmer-cell differentiation were inhibited by CP. Additionally, transcription of the flagellin gene flaA and of flhD, the first gene of the flagellar master operon flhDC, decreased during exposure of P. mirabilis to various concentrations of CP. Moreover, using ureD-gfp, a fusion of the urease accessory gene ureD with gfp, we show that CP inhibits urease expression. Because we demonstrate that CP does not inhibit the growth of P. mirabilis, the observed effects are not attributable to toxicity. Taken together, our results demonstrate that CP hinders motility of P. mirabilis and reduces the expression of important virulence factors.

Comparison of phenotypic and virulence genes characteristics in human and chicken isolates of Proteus mirabilis

The objective of this work is to compare the phenotypic and virulence genes characteristics in human and chicken isolates of Proteus mirabilis. The bacterial examination of 50 livers of individual broilers, marketed by four major outlets, revealed a high recovery of P. mirabilis (66%), and a low recovery frequency of Salmonella spp. (4%), Serratia odorifera (2%), Citrobacter brakii (2%), and Providencia stuartii (2%). The phenotypic biochemical characterization of the recovered 33 chicken isolates of P. mirabilis were compared to 30 human isolates (23 urinary and six respiratory isolates). The comparison revealed significant differences in the presence of gelatinase enzyme (100% presence in chicken isolates versus 91.3 and 83.3% presence in human urinary and respiratory isolates, respectively, P,0.05). The H(2)S production occurred in 100% of chicken isolates versus 95.6 and 66.7% presence in human urinary and respiratory isolates, respectively, P,0.05). The other 17 biochemical characteristics did not differ significantly among the three groups of isolates (P.0.05). Two virulence genes, the mrpA and FliL, were having a typical 100% presence in randomly selected isolates of P. mirabilis recovered from chicken livers (N510) versus isolates recovered from urinary (N55) and respiratory specimens of humans (N55) (P.0.05). The average percentage similarity of mrpA gene nucleotide sequence of poultry isolates to human urinary and respiratory isolates was 93.2 and 97.5-%, respectively. The high similarity in phenotypic characteristics, associated with typical frequency of presence of two virulence genes, and high similarity in sequences of mrpA gene among poultry versus human P. mirabilis isolates justifies future investigations targeting the evaluation of adaptable pathogenicity of avian Proteus mirabilis isolates to mammalian hosts.

Anaerobic respiration using a complete oxidative TCA cycle drives multicellular swarming in Proteus mirabilis

Proteus mirabilis rapidly migrates across surfaces using a periodic developmental process of differentiation alternating between short swimmer cells and elongated hyperflagellated swarmer cells. To undergo this vigorous flagellum-mediated motility, bacteria must generate a substantial proton gradient across their cytoplasmic membranes by using available energy pathways. We sought to identify the link between energy pathways and swarming differentiation by examining the behavior of defined central metabolism mutants. Mutations in the tricarboxylic acid (TCA) cycle (fumC and sdhB mutants) caused altered patterns of swarming periodicity, suggesting an aerobic pathway. Surprisingly, the wild-type strain swarmed on agar containing sodium azide, which poisons aerobic respiration; the fumC TCA cycle mutant, however, was unable to swarm on azide. To identify other contributing energy pathways, we screened transposon mutants for loss of swarming on sodium azide and found insertions in the following genes that involved fumarate metabolism or respiration: hybB, encoding hydrogenase; fumC, encoding fumarase; argH, encoding argininosuccinate lyase (generates fumarate); and a quinone hydroxylase gene. These findings validated the screen and suggested involvement of anaerobic electron transport chain components. Abnormal swarming periodicity of fumC and sdhB mutants was associated with the excretion of reduced acidic fermentation end products. Bacteria lacking SdhB were rescued to wild-type pH and periodicity by providing fumarate, independent of carbon source but dependent on oxygen, while fumC mutants were rescued by glycerol, independent of fumarate only under anaerobic conditions. These findings link multicellular swarming patterns with fumarate metabolism and membrane electron transport using a previously unappreciated configuration of both aerobic and anaerobic respiratory chain components.

Bacterial locomotion and the existence of microbes were the first scientific observations that followed the invention of the microscope. A bacterium can swim through a fluid environment or coordinate motion with a group of bacteria and swarm across a surface. The flagellar motor, which propels the bacterium, is fueled by proton motive force. In contrast to the physiology that governs swimming motility, much less is known about the energy sources required for multicellular swarming on surfaces. In this study, we used Proteus mirabilis as a model organism to study vigorous swarming behavior and genetic and biochemical approaches to define energy pathways and central metabolism that contribute to multicellular motility. We found that swarming bacteria use a complete aerobic tricarboxylic acid (TCA) cycle but do not respire oxygen as the terminal electron acceptor, suggesting that multicellular cooperation during swarming reduces the amount of energy required by individual bacteria to achieve rapid motility.

Merging mythology and morphology: the multifaceted lifestyle of Proteus mirabilis

Proteus mirabilis, named for the Greek god who changed shape to avoid capture, has fascinated microbiologists for more than a century with its unique swarming differentiation, Dienes line formation and potent urease activity. Transcriptome profiling during both host infection and swarming motility, coupled with the availability of the complete genome sequence for P. mirabilis, has revealed the occurrence of interbacterial competition and killing through a type VI secretion system, and the reciprocal regulation of adhesion and motility, as well as the intimate connections between metabolism, swarming and virulence. This Review addresses some of the unique and recently described aspects of P. mirabilis biology and pathogenesis, and emphasizes the potential role of this bacterium in single-species and polymicrobial urinary tract infections.

Transcriptome of Proteus mirabilis in the murine urinary tract: virulence and nitrogen assimilation gene expression

The enteric bacterium Proteus mirabilis is a common cause of complicated urinary tract infections. In this study, microarrays were used to analyze P. mirabilis gene expression in vivo from experimentally infected mice. Urine was collected at 1, 3, and 7 days postinfection, and RNA was isolated from bacteria in the urine for transcriptional analysis. Across nine microarrays, 471 genes were upregulated and 82 were downregulated in vivo compared to in vitro broth culture. Genes upregulated in vivo encoded mannose-resistant Proteus-like (MR/P) fimbriae, urease, iron uptake systems, amino acid and peptide transporters, pyruvate metabolism enzymes, and a portion of the tricarboxylic acid (TCA) cycle enzymes. Flagella were downregulated. Ammonia assimilation gene glnA (glutamine synthetase) was repressed in vivo, while gdhA (glutamate dehydrogenase) was upregulated in vivo. Contrary to our expectations, ammonia availability due to urease activity in P. mirabilis did not drive this gene expression. A gdhA mutant was growth deficient in minimal medium with citrate as the sole carbon source, and loss of gdhA resulted in a significant fitness defect in the mouse model of urinary tract infection. Unlike Escherichia coli, which represses gdhA and upregulates glnA in vivo and cannot utilize citrate, the data suggest that P. mirabilis uses glutamate dehydrogenase to monitor carbon-nitrogen balance, and this ability contributes to the pathogenic potential of P. mirabilis in the urinary tract.

Adhesion, invasion, and agglutination mediated by two trimeric autotransporters in the human uropathogen Proteus mirabilis

Fimbriae of the human uropathogen Proteus mirabilis are the only characterized surface proteins that contribute to its virulence by mediating adhesion and invasion of the uroepithelia. PMI2122 (AipA) and PMI2575 (TaaP) are annotated in the genome of strain HI4320 as trimeric autotransporters with "adhesin-like" and "agglutinating adhesin-like" properties, respectively. The C-terminal 62 amino acids (aa) in AipA and 76 aa in TaaP are homologous to the translocator domains of YadA from Yersinia enterocolitica and Hia from Haemophilus influenzae. Comparative protein modeling using the Hia three-dimensional structure as a template predicted that each of these domains would contain four antiparallel beta sheets and that they formed homotrimers. Recombinant AipA and TaaP were seen as ∼28 kDa and ∼78 kDa, respectively, in Escherichia coli, and each also formed high-molecular-weight homotrimers, thus supporting this model. E. coli synthesizing AipA or TaaP bound to extracellular matrix proteins with a 10- to 60-fold-higher level of affinity than the control strain. Inactivation of aipA in P. mirabilis strains significantly (P < 0.01) reduced the mutants' ability to adhere to or invade HEK293 cell monolayers, and the functions were restored upon complementation. A 51-aa-long invasin region in the AipA passenger domain was required for this function. E. coli expressing TaaP mediated autoagglutination, and a taaP mutant of P. mirabilis showed significantly (P < 0.05) more reduced aggregation than HI4320. Gly-247 in AipA and Gly-708 in TaaP were indispensable for trimerization and activity. AipA and TaaP individually offered advantages to P. mirabilis in a murine model. This is the first report characterizing trimeric autotransporters in P. mirabilis as afimbrial surface adhesins and autoagglutinins.

Tamm-horsfall protein protects against urinary tract infection by proteus mirabilis

PURPOSE

Proteus mirabilis is a common cause of urinary tract infection. We determined the role of Tamm-Horsfall protein as a host defense factor against the cystitis and pyelonephritis caused by P. mirabilis.

MATERIALS AND METHODS

We generated Tamm-Horsfall protein gene knockout mice using homologous recombination. We introduced P. mirabilis transurethrally into the bladder of Tamm-Horsfall protein deficient (THP(-/-)) and genetically similar WT (THP(+/+)) mice. We cultured urine to quantitate the degree of bacteriuria. We examined bladders and kidneys grossly and histomorphometrically to determine the intensity of inflammation.

RESULTS

THP(-/-) mice had more severe bacteriuria and cystitis than THP(+/+) mice. THP(-/-) mice had more pyelonephritic abscesses than THP(+/+) mice. The severity of histological pyelonephritis on semiquantitative histomorphometric analysis appeared to be greater in THP(-/-) mice. The difference between the 2 groups approached but did not attain statistical significance (p = 0.053).

CONCLUSION

Tamm-Horsfall protein acts as a host defense factor against P. mirabilis induced urinary tract infection.