New aspects of the role of MR/P fimbriae in Proteus mirabilis urinary tract infection

Relevance of iron metabolic genes in biofilm and infection in uropathogenic Proteus mirabilis

The microorganisms are found in the environment, forming sessile communities embedded in an extracellular matrix of their own production, called biofilm. These communities have a great relevance in the clinical context, since they are associated with infections caused by biofilm in medical implants, such as urinary catheters. The development of biofilms is a complex process where a great diversity of genes participate. The present work is based on the study of genes related to iron metabolism and its implication in the development of P. mirabilis biofilms and pathogenicity. For this study, two mutant strains defective in biofilm formation were selected, generated by the interruption of genes that encoded non-heme ferritin and TonB-dependent receptor. The mutations influence on the development of the biofilm was evaluated by different approaches. The complexity of the biofilm was analyzed using Confocal Laser Microscopy and image analysis. The mutants infectivity potential was assessed in two experimental mice models of urinary tract infection. The results obtained in the present work show us the role of the ferritin and a TonB-associated porin protein over the initial and later stages of biofilm development. Moreover, in the ascending UTI mouse model, both mutants failed to colonize the urinary tract. In CAUTI models, ferritin mutant damaged the bladder similarly to wild type but the Ton-B mutant was unable to generate infection in the urinary tract. The results obtained in the present work confirm the relevant role that iron metabolism genes have in P. mirabilis biofilm development and for infection in the urinary tract.

MrpH, a new class of metal-binding adhesin, requires zinc to mediate biofilm formation

Proteus mirabilis, a Gram-negative uropathogen, is a major causative agent in catheter-associated urinary tract infections (CAUTI). Mannose-resistant Proteus-like fimbriae (MR/P) are crucially important for P. mirabilis infectivity and are required for biofilm formation and auto-aggregation, as well as for bladder and kidney colonization. Here, the X-ray crystal structure of the MR/P tip adhesin, MrpH, is reported. The structure has a fold not previously described and contains a transition metal center with Zn²⁺ coordinated by three conserved histidine residues and a ligand. Using biofilm assays, chelation, metal complementation, and site-directed mutagenesis of the three histidines, we show that an intact metal binding site occupied by zinc is essential for MR/P fimbria-mediated biofilm formation, and furthermore, that P. mirabilis biofilm formation is reversible in a zinc-dependent manner. Zinc is also required for MR/P-dependent agglutination of erythrocytes, and mutation of the metal binding site renders P. mirabilis unfit in a mouse model of UTI. The studies presented here provide important clues as to the mechanism of MR/P-mediated biofilm formation and serve as a starting point for identifying the physiological MR/P fimbrial receptor.

Many bacteria use fimbriae to adhere to surfaces, and this function is often essential for pathogens to gain a foothold in the host. In this study, we examine the major virulence-associated fimbrial protein, MrpH, of the bacterial urinary tract pathogen Proteus mirabilis. This species is particularly known for causing catheter-associated urinary tract infections, in which it forms damaging urinary stones and crystalline biofilms that can block the flow of urine through indwelling catheters. MrpH resides at the tip of mannose-resistant Proteus-like (MR/P) fimbriae and is required for MR/P-dependent adherence to surfaces. Although MR/P belongs to a well-known class of adhesive fimbriae encoded by the chaperone-usher pathway, we found that MrpH has a dramatically different structure compared with other tip-located adhesins in this family. Unexpectedly, MrpH was found to bind a zinc cation, which we show is essential for MR/P-mediated biofilm formation and adherence to red blood cells. Furthermore, MR/P-mediated adherence can be modified by controlling zinc levels. These findings have the potential to aid development of better anti-biofilm urinary catheters or other methods to prevent P. mirabilis infection of the urinary tract.

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.

MrpJ Directly Regulates Proteus mirabilis Virulence Factors, Including Fimbriae and Type VI Secretion, during Urinary Tract Infection

Proteus mirabilis is a leading cause of catheter-associated urinary tract infections (CAUTIs) and urolithiasis. The transcriptional regulator MrpJ inversely modulates two critical aspects of P. mirabilis UTI progression: fimbria-mediated attachment and flagellum-mediated motility. Transcriptome data indicated a network of virulence-associated genes under MrpJ's control. Here, we identify the direct gene regulon of MrpJ and its contribution to P. mirabilis pathogenesis, leading to the discovery of novel virulence targets. Chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq) was used for the first time in a CAUTI pathogen to probe for in vivo direct targets of MrpJ. Selected MrpJ-regulated genes were mutated and assessed for their contribution to UTI using a mouse model. ChIP-seq revealed a palindromic MrpJ binding sequence and 78 MrpJ-bound regions, including binding sites upstream of genes involved in motility, fimbriae, and a type VI secretion system (T6SS). A combinatorial mutation approach established the contribution of three fimbriae (fim8A, fim14A, and pmpA) to UTI and a new pathogenic role for the T6SS in UTI progression. In conclusion, this study (i) establishes the direct gene regulon and an MrpJ consensus binding site and (ii) led to the discovery of new virulence genes in P. mirabilis UTI, which could be targeted for therapeutic intervention of CAUTI.

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.

Fimbriae have distinguishable roles in Proteus mirabilis biofilm formation

Proteus mirabilis is one of the most common etiological agents of complicated urinary tract infections, especially those associated with catheterization. This is related to the ability of P. mirabilis to form biofilms on different surfaces. This pathogen encodes 17 putative fimbrial operons, the highest number found in any sequenced bacterial species so far. The present study analyzed the role of four P. mirabilis fimbriae (MR/P, UCA, ATF and PMF) in biofilm formation using isogenic mutants. Experimental approaches included migration over catheter, swimming and swarming motility, the semiquantitative assay based on adhesion and crystal violet staining, and biofilm development by immunofluorescence and confocal microscopy. Different assays were performed using LB or artificial urine. Results indicated that the different fimbriae contribute to the formation of a stable and functional biofilm. Fimbriae revealed particular associated roles. First, all the mutants showed a significantly reduced ability to migrate across urinary catheter sections but neither swimming nor swarming motility were affected. However, some mutants formed smaller biofilms compared with the wild type (MRP and ATF) while others formed significantly larger biofilms (UCA and PMF) showing different bioarchitecture features. It can be concluded that P. mirabilis fimbriae have distinguishable roles in the generation of biofilms, particularly in association with catheters.

Structure, Function, and Assembly of Adhesive Organelles by Uropathogenic Bacteria

Bacteria assemble a wide range of adhesive proteins, termed adhesins, to mediate binding to receptors and colonization of surfaces. For pathogenic bacteria, adhesins are critical for early stages of infection, allowing the bacteria to initiate contact with host cells, colonize different tissues, and establish a foothold within the host. The adhesins expressed by a pathogen are also critical for bacterial-bacterial interactions and the formation of bacterial communities, including biofilms. The ability to adhere to host tissues is particularly important for bacteria that colonize sites such as the urinary tract, where the flow of urine functions to maintain sterility by washing away non-adherent pathogens. Adhesins vary from monomeric proteins that are directly anchored to the bacterial surface to polymeric, hair-like fibers that extend out from the cell surface. These latter fibers are termed pili or fimbriae, and were among the first identified virulence factors of uropathogenic Escherichia coli. Studies since then have identified a range of both pilus and non-pilus adhesins that contribute to bacterial colonization of the urinary tract, and have revealed molecular details of the structures, assembly pathways, and functions of these adhesive organelles. In this review, we describe the different types of adhesins expressed by both Gram-negative and Gram-positive uropathogens, what is known about their structures, how they are assembled on the bacterial surface, and the functions of specific adhesins in the pathogenesis of urinary tract infections.

Multidrug-Resistant Proteus mirabilis Isolated From Newly Weaned Infant Rhesus Monkeys and Ferrets

Background:

Proteus mirabilis is an important uropathogen that causes complicated Urinary Tract Infection (UTI) and induces diarrhea in infants.

Objectives:

This study aimed to investigate P. mirabilis infection in newly weaned infant rhesus monkeys (Macaca mulatta) and ferrets (Mustela putorius furo) with diarrhea.

Materials and Methods:

Stool samples were collected from 74 rhesus monkeys and 12 ferrets with diarrhea. Proteus mirabilis was isolated from the samples through Polymerase Chain Reaction. The isolated P. mirabilis was subjected to antimicrobial susceptibility tests.

Results:

Seven (7/74, 9.5%) and four (4/12, 30%) P. mirabilis strains were detected in the stool samples collected from the monkeys and ferrets, respectively. Sequence analyses showed that the isolated P. mirabilis was closely related to P. mirabilis strain HI4320, which was isolated from the urine of a patient with a long-term indwelling urinary catheter. In addition, the isolates demonstrated multidrug resistance.

Conclusions:

Rhesus monkeys and ferrets are susceptible to P. mirabilis, making them useful as animal models for future studies on the mechanism of P. mirabilis-induced UTI and its corresponding treatment.

Intranasal immunization with fusion protein MrpH·FimH and MPL adjuvant confers protection against urinary tract infections caused by uropathogenic Escherichia coli and Proteus mirabilis

Urinary tract infections (UTIs) caused by Uropathogenic Escherichia coli (UPEC) and Proteus mirabilis are among the most common infections in the world. Currently there are no vaccines available to confer protection against UTI in humans. In this study, the immune responses and protection of FimH of UPEC with MrpH antigen of P. mirabilis in different vaccine formulations with and without MPL adjuvant were assessed. Mice intranasally immunized with the novel fusion protein MrpH·FimH induced a significant increase in IgG and IgA in serum, nasal wash, vaginal wash, and urine samples. Mice immunized with fusion MrpH·FimH also showed a significant boost in cellular immunity. Addition of MPL as the adjuvant enhanced FimH and MrpH specific humoral and cellular responses in both systemic and mucosal samples. Vaccination with MrpH·FimH alone or in combination with MPL showed the highest efficiency in clearing bladder and kidney infections in mice challenged with UPEC and P. mirabilis. These findings may indicate that the protection observed correlates with the systemic, mucosal and cellular immune responses induced by vaccination with these preparations. Our data suggest MrpH·FimH fusion protein with or without MPL as adjuvant could be potential vaccine candidates for elimination of UPEC and P. mirabilis. These data altogether are promising and these formulations are good candidates for elimination of UPEC and P. mirabilis.

New aspects of RpoE in uropathogenic Proteus mirabilis

Proteus mirabilis is a common human pathogen causing recurrent or persistent urinary tract infections (UTIs). The underlying mechanisms for P. mirabilis to establish UTIs are not fully elucidated. In this study, we showed that loss of the sigma factor E (RpoE), mediating extracytoplasmic stress responses, decreased fimbria expression, survival in macrophages, cell invasion, and colonization in mice but increased the interleukin-8 (IL-8) expression of urothelial cells and swarming motility. This is the first study to demonstrate that RpoE modulated expression of MR/P fimbriae by regulating mrpI, a gene encoding a recombinase controlling the orientation of MR/P fimbria promoter. By real-time reverse transcription-PCR, we found that the IL-8 mRNA amount of urothelial cells was induced significantly by lipopolysaccharides extracted from rpoE mutant but not from the wild type. These RpoE-associated virulence factors should be coordinately expressed to enhance the fitness of P. mirabilis in the host, including the avoidance of immune attacks. Accordingly, rpoE mutant-infected mice displayed more immune cell infiltration in bladders and kidneys during early stages of infection, and the rpoE mutant had a dramatically impaired ability of colonization. Moreover, it is noteworthy that urea (the major component in urine) and polymyxin B (a cationic antimicrobial peptide) can induce expression of rpoE by the reporter assay, suggesting that RpoE might be activated in the urinary tract. Altogether, our results indicate that RpoE is important in sensing environmental cues of the urinary tract and subsequently triggering the expression of virulence factors, which are associated with the fitness of P. mirabilis, to build up a UTI.

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.

Proteus mirabilis uroepithelial cell adhesin (UCA) fimbria plays a role in the colonization of the urinary tract

Urinary tract infections (UTIs) are among the most common bacterial infections in humans. Proteus mirabilis is an opportunistic pathogen, capable of causing severe UTIs, with serious kidney damage that may even lead to death. Several virulence factors are involved in the pathogenicity of this bacterium. Among these, adherence to the uroepithelium mediated by fimbriae appears to be a significant bacterial attribute related to urovirulence. Proteus mirabilis expresses several types of fimbriae that could be involved in the pathogenesis of UTI, including uroepithelial cell adhesin (UCA). In this report, we used an uropathogenic P. mirabilis wild-type strain and an isogenic ucaA mutant unable to express UCA to study the pathogenic role of this fimbria in UTI. Ability of the mutant to adhere to desquamated uroepithelial cells and to infect mice using different experimental UTI models was significantly impaired. These results allow us to conclude that P. mirabilis UCA plays an important role in the colonization of the urinary tract.

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.

Development of 3D architecture of uropathogenic Proteus mirabilis batch culture biofilms-A quantitative confocal microscopy approach

This work studies the development of the 3D architecture of batch culture P. mirabilis biofilms on the basis of morpho-topological descriptors calculated from confocal laser scanning microscopy (CLSM) stacks with image processing routines. A precise architectonical understanding of biofilm organization on a morpho-topological level is necessary to understand emergent interactions with the environment and the appearance of functionally different progeny swarmer cells. P. mirabilis biofilms were grown on glass coverslips for seven days on LB broth and subjected to in situ immunofluorescence. Confocal image stacks were deconvolved prior to segmentation of regions of interest (ROI) that identify individual bacteria and extracellular material, followed by 3D reconstruction and calculation of different morpho-topological key descriptors. Results showed that P. mirabilis biofilm formation followed a five stage process: (i) reversible adhesion to the surface characterized by slow growth, presence of elongated bacteria, and absence of extracellular material, (ii) irreversible bacterial adhesion concomitant to decreasing elongation, and the beginning of extracellular polymer production, (iii) accelerated bacterial growth concomitant to continuously decreasing elongation and halting of extracellular polymer production, (iv) maturation of biofilm defined by maximum bacterial density, volume, minimum elongation, maximum extracellular material, and highest compaction, and (v) decreased bacterial density and extracellular material through detachment and dispersion. Swarmer cells do not play a role in P. mirabilis biofilm formation under the applied conditions. Our approach sets the basis for future studies of 3D biofilm architecture using dynamic in vivo models and different environmental conditions that assess clinical impacts of P. mirabilis biofilm.

Effects of the administration of cholera toxin as a mucosal adjuvant on the immune and protective response induced by Proteus mirabilis MrpA fimbrial protein in the urinary tract

Proteus mirabilis is commonly associated with complicated UTI and expresses several virulence factors, including MR/P fimbriae. In the present study mice were immunised nasally with MrpA, the structural subunit of MR/P, with or without CT as a mucosal adjuvant. The animals were then challenged with P. mirabilis and induction of specific serum and urine IgG and IgA, IFN-gamma production and bacterial kidney and bladder colonization were assessed. MrpA-immunised mice exhibited significant induction of serum IgA and urine IgA and IgG. MrpA/CT-immunised mice showed both significant serum and urine IgA and IgG production. Only this group showed significant IFN-y production. Both groups of animals had significant decrease in bacterial colonization of kidneys but not of bladders. No correlation between specific antibody induction in serum and CFU decrease was observed in any group of animals. Our results suggest that a mucosal adjuvant (CT) in the urinary tract enhanced humoral and cytokine response although it did not influence the degree of protection against UTI provided by MrpA. Further studies are necessary to understand immune modulation in the urinary tract.

Identification of virulence determinants in uropathogenic Proteus mirabilis using signature-tagged mutagenesis

The Gram-negative bacterium Proteus mirabilis causes urinary tract infections (UTIs) in individuals with long-term indwelling catheters or those with functional or structural abnormalities of the urinary tract. Known virulence factors include urease, haemolysin, fimbriae, flagella, DsbA, a phosphate transporter and genes involved in cell-wall synthesis and metabolism, many of which have been identified using the technique of signature-tagged mutagenesis (STM). To identify additional virulence determinants and to increase the theoretical coverage of the genome, this study generated and assessed 1880 P. mirabilis strain HI4320 mutants using this method. Mutants with disruptions in genes vital for colonization of the CBA mouse model of ascending UTI were identified after performing primary and secondary in vivo screens in approximately 315 CBA mice, primary and secondary in vitro screens in both Luria broth and minimal A medium to eliminate mutants with minor growth deficiencies, and co-challenge competition experiments in approximately 500 CBA mice. After completion of in vivo screening, a total of 217 transposon mutants were attenuated in the CBA mouse model of ascending UTI. Following in vitro screening, this number was reduced to 196 transposon mutants with a probable role in virulence. Co-challenge competition experiments confirmed significant attenuation for 37 of the 93 transposon mutants tested, being outcompeted by wild-type HI4320. Following sequence analysis of the 37 mutants, transposon insertions were identified in genes including the peptidyl-prolyl isomerases surA and ppiA, glycosyltransferase cpsF, biopolymer transport protein exbD, transcriptional regulator nhaR, one putative fimbrial protein, flagellar M-ring protein fliF and hook protein flgE, and multiple metabolic genes.

ZapA, a virulence factor in a rat model of Proteus mirabilis-induced acute and chronic prostatitis

Our knowledge of pathogenesis has benefited from a better understanding of the roles of specific virulence factors in disease. To determine the role of the virulence factor ZapA, a 54-kDa metalloproteinase of Proteus mirabilis, in prostatitis, rats were infected with either wild-type (WT) P. mirabilis or its isogenic ZapA(-) mutant KW360. The WT produced both acute and chronic prostatitis showing the typical histological progressions that are the hallmarks of these diseases. Infection with the ZapA(-) mutant, however, resulted in reduced levels of acute prostatitis, as determined from lower levels of tissue damage, bacterial colonization, and inflammation. Further, the ZapA(-) mutant failed to establish a chronic infection, in that bacteria were cleared from the prostate, inflammation was resolved, and tissue was seen to be healing. Clearance from the prostate was not the result of a reduced capacity of the ZapA(-) mutant to form biofilms in vitro. These finding clearly define ZapA as an important virulence factor in both acute and chronic bacterial prostatitis.

An iron-regulated outer-membrane protein of Proteus mirabilis is a haem receptor that plays an important role in urinary tract infection and in in vivo growth

Proteus mirabilis, a common cause of urinary tract infections, expresses iron-regulated outer-membrane proteins (OMPs) in response to iron restriction. It has been suggested that a 64 kDa OMP is involved in haemoprotein uptake and that this might have a role in pathogenesis. In order to confirm this hypothesis, this study generated a P. mirabilis mutant strain (P7) that did not express the 64 kDa OMP, by insertion of the TnphoA transposon. The nucleotide sequence of the interrupted gene revealed that it corresponded to a haemin receptor precursor. Moreover, in vitro growth assays showed that the mutant was unable to grow using haemoglobin and haemin as unique iron sources. The authors also carried out in vivo growth and infectivity assays and demonstrated that P7 was not able to survive in an in vivo model and was less efficient than wild-type strain Pr 6515 in colonizing the urinary tract. These results confirmed that the P. mirabilis 64 kDa iron-regulated OMP is a haem receptor that has an important role for survival and multiplication of these bacteria in the mammalian host and in the development of urinary tract infection.

Intranasal immunisation with recombinant Lactococcus lactis displaying either anchored or secreted forms of Proteus mirabilis MrpA fimbrial protein confers specific immune response and induces a significant reduction of kidney bacterial colonisation in mice

Proteus mirabilis, a common cause of urinary tract infections in humans, can express different fimbriae. MR/P fimbriae may contribute to bacterial colonisation, and its structural protein MrpA represents a promising candidate antigen for mucosal vaccination. Commercial complex vaccines have limited, short-lived protection and are incapable of eliciting mucosal responses against putative antigens related to virulence. The development of mucosal live vaccines using food-grade lactic acid bacterium Lactococcus lactis as antigen vehicle is an attractive alternative and a safe vaccination strategy against P. mirabilis infection. Here, we report the construction of L. lactis strains modified to produce MrpA via two cellular locations, cell wall-anchored and secreted. Protection assays against P. mirabilis infection and evaluation of the immune response generated after immunisation were conducted in a mouse model. MrpA protein was efficiently expressed by L. lactis strain and caused a significant induction of specific serum IgG and IgA in the animals immunised with L. lactis pSEC:mrpA and L. lactis pCWA:mrpA respectively. A significant reduction of renal bacterial colonisation was observed in both groups of mice (P<0.05) after P. mirabilis challenge. This is the first example of a P. mirabilis fimbrial antigen expressed in a food-grade live strain with promising applications in vaccine design.

Proteus mirabilis isolates of different origins do not show correlation with virulence attributes and can colonize the urinary tract of mice

Proteus mirabilis has been described as an aetiological agent in a wide range of infections, playing an important role in urinary tract infections (UTIs). In this study, a collection of P. mirabilis isolates obtained from clinical and non-clinical sources was analysed in order to determine a possible correlation between origin, virulence factors and in vivo infectivity. Isolates were characterized in vitro, assessing several virulence properties that had been previously associated with P. mirabilis uropathogenicity. Swarming motility, urease production, growth in urine, outer-membrane protein patterns, ability to grow in the presence of different iron sources, haemolysin and haemagglutinin production, and the presence and expression of diverse fimbrial genes, were analysed. In order to evaluate the infectivity of the different isolates, the experimental ascending UTI model in mice was used. Additionally, the Dienes test and the enterobacterial repetitive intergenic consensus (ERIC)-PCR assay were performed to assess the genetic diversity of the isolates. The results of the present study did not show any correlation between distribution of the diverse potential urovirulence factors and isolate source. No significant correlation was observed between infectivity and the origin of the isolates, since they all similarly colonized the urinary tract of the challenged mice. Finally, all isolates showed unique ERIC-PCR patterns, indicating that the isolates were genetically diverse. The results obtained in this study suggest that the source of P. mirabilis strains cannot be correlated with pathogenic attributes, and that the distribution of virulence factors between isolates of different origins may correspond to the opportunistic nature of the organism.

Proteus mirabilis fimbriae (PMF) are important for both bladder and kidney colonization in mice

Proteus mirabilis expresses different types of fimbriae simultaneously. Several fimbrial types have been described and their role in the colonization of the urinary tract is under study. Previously, P. mirabilis fimbriae (PMF) have been shown to be associated with bacterial colonization of the lower urinary tract but not of the kidneys. In this study, a pmfA mutant was generated and used in several in vivo and in vitro studies. Two different urinary tract infection models in the mouse and two in vitro assays of bacterial adhesion to uroepithelial cells were performed. Expression of PmfA in a collection of P. mirabilis strains of different sources was also assessed. The results shown here indicate that PMF are involved in both bladder and kidney colonization by P. mirabilis and that these fimbriae are widely distributed among P. mirabilis isolates from different origins since all strains tested expressed PmfA.

Evaluation of Proteus mirabilis structural fimbrial proteins as antigens against urinary tract infections

Proteus mirabilis is a common cause of urinary tract infection (UTI) and produce several types of different fimbriae, including mannose-resistant/Proteus-like fimbriae, uroepithelial cell adhesin (UCA), and P. mirabilis fimbriae (PMF). Different authors have related these fimbriae with different aspects of P. mirabilis pathogenesis, although the precise role of fimbriae in UTI has not yet been elucidated. In this work we expressed and purified recombinant structural fimbrial proteins of these fimbriae (MrpA, UcaA, and PmfA) and assessed their role as protective antigens using an ascending and a haematogenous model of UTI in the mouse. MrpA protected subcutaneously immunised mice in both models, suggesting that it could be taken into account as a promising vaccine candidate against P. mirabilis UTI. UcaA could also be an interesting subunit to be studied although it only protected mice that were challenged intravenously. All subunits elicited a strong specific serum IgG response but there was no significant correlation between antibody levels and protection. Only PmfA-immunised mice elicited a significant urinary antibody response but this protein was unable to confer protection against P. mirabilis experimental challenges. These results may contribute to the development of vaccines against P. mirabilis, an important cause of complicated UTI.