Proteus mirabilis genes that contribute to pathogenesis of urinary tract infection: identification of 25 signature-tagged mutants attenuated at least 100-fold

Loss of the waaL O-antigen ligase prevents surface activation of the flagellar gene cascade in Proteus mirabilis

Proteus mirabilis is a Gram-negative bacterium that undergoes a physical and biochemical change from a vegetative swimmer cell (a typical Gram-negative rod) to an elongated swarmer cell when grown on a solid surface. In this study, we report that a transposon insertion in the waaL gene, encoding O-antigen ligase, blocked swarming motility on solid surfaces but had little effect on swimming motility in soft agar. The waaL mutant was unable to differentiate into a swarmer cell. Differentiation was also prevented by a mutation in wzz, encoding a chain length determinant for O antigen, but not by a mutation in wzyE, encoding an enzyme that polymerizes enterobacterial common antigen, a surface polysaccharide different from the lipid A::core. In wild-type P. mirabilis, increased expression of the flhDC operon occurs after growth on solid surfaces and is required for the high-level expression of flagellin that is characteristic of swarmer cells. However, in both the waaL and the wzz mutants, the flhDC operon was not activated during growth on agar. A loss-of-function mutation in the rcsB response regulator or overexpression of flhDC restored swarming to the waaL mutant, despite the absence of O antigen. Therefore, although O antigen may serve a role in swarming by promoting wettability, the loss of O antigen blocks a regulatory pathway that links surface contact with the upregulation of flhDC expression.

Transcriptome of swarming Proteus mirabilis

Swarming motility by the urinary tract pathogen Proteus mirabilis has been a long-studied but little understood phenomenon. On agar, a P. mirabilis colony grows outward in a bull's-eye pattern formed by consecutive waves of rapid swarming followed by consolidation into shorter cells. To examine differential gene expression in these growth phases, a microarray was constructed based on the completed genome sequence and annotation. RNA was extracted from broth-cultured, swarming, and consolidation-phase cells to assess transcription during each of these growth states. A total of 587 genes were differentially expressed in broth-cultured cells versus swarming cells, and 527 genes were differentially expressed in broth-cultured cells versus consolidation-phase cells (consolidate). Flagellar genes were highly upregulated in both swarming cells and consolidation-phase cells. Fimbriae were downregulated in swarming cells, while genes involved in cell division and anaerobic growth were upregulated in broth-cultured cells. Direct comparison of swarming cells to consolidation-phase cells found that 541 genes were upregulated in consolidate, but only nine genes were upregulated in swarm cells. Genes involved in flagellar biosynthesis, oligopeptide transport, amino acid import and metabolism, cell division, and phage were upregulated in consolidate. Mutation of dppA, oppB, and cysJ, upregulated during consolidation compared to during swarming, revealed that although these genes play a minor role in swarming, dppA and cysJ are required during ascending urinary tract infection. Swarming on agar to which chloramphenicol had been added suggested that protein synthesis is not required for swarming. These data suggest that the consolidation phase is a state in which P. mirabilis prepares for the next wave of swarming.

Identification of genes involved in the mutualistic colonization of the nematode Heterorhabditis bacteriophora by the bacterium Photorhabdus luminescens

Background

Photorhabdus are Gram negative entomopathogenic bacteria that also have a mutualistic association with nematodes from the family Heterorhabditis. An essential part of this symbiosis is the ability of the bacterium to colonize the gut of the freeliving form of the nematode called the infective juvenile (IJ). Although the colonization process (also called transmission) has been described phenomonologically very little is known about the underlying molecular mechanisms. Therefore, in this study, we were interested in identifying genes in Photorhabdus that are important for IJ colonization.

Results

In this work we genetically tagged P. luminescens TT01 with gfp and constructed a library containing over 3200 mutants using the suicide vector, pUT-Km2. Using a combination of in vitro symbiosis assays and fluorescent microscopy we screened this library for mutants that were affected in their ability to colonize the IJ i.e. with decreased transmission frequencies. In total 8 mutants were identified with transmission frequencies of ≤ 30% compared to wild-type. These mutants were mapped to 6 different genetic loci; the pbgPE operon, galE, galU, proQ, asmA and hdfR. The pbgPE, galE and galU mutants were all predicted to be involved in LPS biosynthesis and, in support of this, we have shown that these mutants are avirulent and sensitive to the cationic antimicriobial peptide, polymyxin B. On the other hand the proQ, asmA and hdfR mutants were not affected in virulence and were either as resistant (proQ) or slightly more sensitive (asmA, hdfR) to polymyxin B than the wild-type (WT).

Conclusions

This is the first report describing the outcome of a comprehensive screen looking for transmission mutants in Photorhabdus. In total 6 genetic loci were identified and we present evidence that all of these loci are involved in the assembly and/or maintenance of LPS and other factors associated with the cell surface. Interestingly several, but not all, of the transmission mutants identified were also avirulent suggesting that there is a significant, but not complete, genetic overlap between pathogenicity and mutualism. Therefore, this study highlights the importance of the cell surface in mediating the symbiotic and pathogenic interactions of Photorhabdus.

Complete genome sequence and comparative metabolic profiling of the prototypical enteroaggregative Escherichia coli strain 042

BACKGROUND

Escherichia coli can experience a multifaceted life, in some cases acting as a commensal while in other cases causing intestinal and/or extraintestinal disease. Several studies suggest enteroaggregative E. coli are the predominant cause of E. coli-mediated diarrhea in the developed world and are second only to Campylobacter sp. as a cause of bacterial-mediated diarrhea. Furthermore, enteroaggregative E. coli are a predominant cause of persistent diarrhea in the developing world where infection has been associated with malnourishment and growth retardation.

METHODS

In this study we determined the complete genomic sequence of E. coli 042, the prototypical member of the enteroaggregative E. coli, which has been shown to cause disease in volunteer studies. We performed genomic and phylogenetic comparisons with other E. coli strains revealing previously uncharacterised virulence factors including a variety of secreted proteins and a capsular polysaccharide biosynthetic locus. In addition, by using Biolog Phenotype Microarrays we have provided a full metabolic profiling of E. coli 042 and the non-pathogenic lab strain E. coli K-12. We have highlighted the genetic basis for many of the metabolic differences between E. coli 042 and E. coli K-12.

CONCLUSION

This study provides a genetic context for the vast amount of experimental and epidemiological data published thus far and provides a template for future diagnostic and intervention strategies.

Identification of a modular pathogenicity island that is widespread among urease-producing uropathogens and shares features with a diverse group of mobile elements

Pathogenicity islands (PAIs) are a specific group of genomic islands that contribute to genomic variability and virulence of bacterial pathogens. Using a strain-specific comparative genomic hybridization array, we report the identification of a 94-kb PAI, designated ICEPm1, that is common to Proteus mirabilis, Providencia stuartii, and Morganella morganii. These organisms are highly prevalent etiologic agents of catheter-associated urinary tract infections (caUTI), the most common hospital acquired infection. ICEPm1 carries virulence factors that are important for colonization of the urinary tract, including a known toxin (Proteus toxic agglutinin) and the high pathogenicity island of Yersinia spp. In addition, this PAI shares homology and gene organization similar to the PAIs of other bacterial pathogens, several of which have been classified as mobile integrative and conjugative elements (ICEs). Isolates from this study were cultured from patients with caUTI and show identical sequence similarity at three loci within ICEPm1, suggesting its transfer between bacterial genera. Screening for the presence of ICEPm1 among P. mirabilis colonizing isolates showed that ICEPm1 is more prevalent in urine isolates compared to P. mirabilis strains isolated from other body sites (P<0.0001), further suggesting that it contributes to niche specificity and is positively selected for in the urinary tract.

Inactivation of the Pseudomonas putida KT2440 dsbA gene promotes extracellular matrix production and biofilm formation

To identify genes essential to biofilm formation in Pseudomonas putida KT2440, 12 mutants defective in oxidative stress-related or metabolic pathway-related genes were evaluated. Of them, only the dsbA mutant lacking the disulfide bond isomerase exhibited significantly increased attachment to the polystyrene surface. Visual evaluation by extracellular matrix staining and scanning electron microscopy indicated that the KT2440-DeltadsbA strain displays enhanced extracellular matrix production, rugose colony morphology on agar plates and floating pellicles in static culture. Accordingly, we propose that deletion of the dsbA gene may stimulate production of the extracellular matrix, resulting in those phenotypes. In addition, the lack of detectable fluorescence in the KT2440-DeltadsbA under UV light as well as in both the wild type and the KT2440-DeltadsbA when grown on Luria-Bertani plates containing ferrous iron suggests that the fluorescent molecule may be a fluorescent siderophore with its synthesis/secretion controlled by DsbA in KT2440. These phenotypic defects observed in the dsbA mutant were complemented by the full-length KT2440 and Escherichia coli dsbA genes. In contrast to the role of DsbA in other bacteria, our results provide the first evidence that disruption of P. putida KT2440 dsbA gene overproduces the extracellular matrix and thus promotes biofilm formation.

Characterization of two homologous disulfide bond systems involved in virulence factor biogenesis in uropathogenic Escherichia coli CFT073

Disulfide bond (DSB) formation is catalyzed by disulfide bond proteins and is critical for the proper folding and functioning of secreted and membrane-associated bacterial proteins. Uropathogenic Escherichia coli (UPEC) strains possess two paralogous disulfide bond systems: the well-characterized DsbAB system and the recently described DsbLI system. In the DsbAB system, the highly oxidizing DsbA protein introduces disulfide bonds into unfolded polypeptides by donating its redox-active disulfide and is in turn reoxidized by DsbB. DsbA has broad substrate specificity and reacts readily with reduced unfolded proteins entering the periplasm. The DsbLI system also comprises a functional redox pair; however, DsbL catalyzes the specific oxidative folding of the large periplasmic enzyme arylsulfate sulfotransferase (ASST). In this study, we characterized the DsbLI system of the prototypic UPEC strain CFT073 and examined the contributions of the DsbAB and DsbLI systems to the production of functional flagella as well as type 1 and P fimbriae. The DsbLI system was able to catalyze disulfide bond formation in several well-defined DsbA targets when provided in trans on a multicopy plasmid. In a mouse urinary tract infection model, the isogenic dsbAB deletion mutant of CFT073 was severely attenuated, while deletion of dsbLI or assT did not affect colonization.

The high-affinity phosphate transporter Pst in Proteus mirabilis HI4320 and its importance in biofilm formation

Proteus mirabilis causes urinary tract infections (UTIs) in individuals requiring long-term indwelling catheterization. The pathogenesis of this uropathogen is mediated by a number of virulence factors and the formation of crystalline biofilms. In addition, micro-organisms have evolved complex systems for the acquisition of nutrients, including the phosphate-specific transport system, which has been shown to be important in biofilm formation and pathogenesis. A functional Pst system is important during UTIs caused by P. mirabilis HI4320, since transposon mutants in the PstS periplasmic binding protein and the PstA permease protein were attenuated in the CBA mouse model of UTI. These mutants displayed a defect in biofilm formation when grown in human urine. This study focuses on a comparison of the proteomes during biofilm and planktonic growth in phosphate-rich medium and human urine, and microscopic investigations of biofilms formed by the pst mutants. Our data suggest that (i) the Deltapst mutants, and particularly the DeltapstS mutant, are defective in biofilm formation, and (ii) the proteomes of these mutants differ significantly from that of the wild-type. Therefore, since the Pst system of P. mirabilis HI4320 negatively regulates biofilm formation, this system is important for the pathogenesis of these organisms during complicated UTIs.

Role of motility and chemotaxis in the pathogenesis of Dickeya dadantii 3937 (ex Erwinia chrysanthemi 3937)

Dickeya dadantii 3937 (ex Erwinia chrysanthemi), a member of the Enterobacteriaceae, causes soft rot in many economically important crops. A successful pathogen has to reach the interior of the plant in order to cause disease. To study the role of motility and chemotaxis in the pathogenicity of D. dadantii 3937, genes involved in the chemotactic signal transduction system (cheW, cheB, cheY and cheZ) and in the structure of the flagellar motor (motA) were mutagenized. All the mutant strains grew like the wild-type in culture media, and the production and secretion of pectolytic enzymes was not affected. As expected, the swimming ability of the mutant strains was reduced with respect to the wild-type: motA (94%), cheY (80%), cheW (74%), cheB (54%) and cheZ (48%). The virulence of the mutant strains was analysed in chicory, Saintpaulia and potato. The mutant strains were also tested for their capability to enter into Arabidopsis leaves. All the mutants showed a significant decrease of virulence in certain hosts; however, the degree of virulence reduction varied depending on the virulence assay. The ability to penetrate Arabidopsis leaves was impaired in all the mutants, whereas the capacity to colonize potato tubers after artificial inoculation was affected in only two mutant strains. In general, the virulence of the mutants could be ranked as motA<cheY<cheB=cheW<cheZ, which correlated with the degree to which swimming was affected. These results clearly indicate that motility plays an important role in the pathogenicity of this bacterium.

Laser interferometric and cultivation methods for measurement of colistin/ampicilin and saponin interactions with smooth and rough of Proteus mirabilis lipopolysaccharides and cells

Laser interferometry is commonly used in permeability studies of soluble substances. In this study a modification that allowed testing partially insoluble mixtures is presented. The modification relies on the measurement of diffusion from 1% agarose gel. As a model for this study, two Proteus mirabilis strains were used that differ in polysaccharide content: smooth P. mirabilis S1959 strain and its Re-type mutant, strain R45. By laser interferometry and precipitation it is shown that R45 lipopolysaccharide is more effective in binding colistin. It has been shown with the laser interferometric method that saponins, which are detergent-like substances of plant origin, partially enhance the interaction of colistin with the S and Re types of P. mirabilis. These results were confirmed with whole cell Proteus studies. The saponin partially inhibited the growth of the S and Re P. mirabilis strains at doses of 31-500 microg/ml. A sub-inhibitory dose--15 microg/ml of saponins alone do not reduced the numbers of P. mirabilis S1959 and R45 cells. However, the presence of colistin or amipicillin and 15 microg/ml of saponins reduced the amount of P. mirabilis S1959 and R45 cells. The saponins enhanced sensitivities of S and R P. mirabilis cells towards colistin and amipicillin. One may proposed that saponins binds to lipid A part of LPS may resulted on an increase in bacterial cell wall outer-membrane permeabilities and by that facilitated antibiotics penetration into the bacterial cells. In conclusion, the laser interferometric method is a useful tool for studies of lipopolysaccharide-antibiotic interactions even if the tested substances are not fully soluble in water.

Oxygen-limiting conditions enrich for fimbriate cells of uropathogenic Proteus mirabilis and Escherichia coli

MR/P fimbriae of uropathogenic Proteus mirabilis undergo invertible element-mediated phase variation whereby an individual bacterium switches between expressing fimbriae (phase ON) and not expressing fimbriae (phase OFF). Under different conditions, the percentage of fimbriate bacteria within a population varies and could be dictated by either selection (growth advantage of one phase) or signaling (preferentially converting one phase to the other in response to external signals). Expression of MR/P fimbriae increases in a cell-density dependent manner in vitro and in vivo. However, rather than the increased cell density itself, this increase in fimbrial expression is due to an enrichment of fimbriate bacteria under oxygen limitation resulting from increased cell density. Our data also indicate that the persistence of MR/P fimbriate bacteria under oxygen-limiting conditions is a result of both selection (of MR/P fimbrial phase variants) and signaling (via modulation of expression of the MrpI recombinase). Furthermore, the mrpJ transcriptional regulator encoded within the mrp operon contributes to phase switching. Type 1 fimbriae of Escherichia coli, which are likewise subject to phase variation via an invertible element, also increase in expression during reduced oxygenation. These findings provide evidence to support a mechanism for persistence of fimbriate bacteria under oxygen limitation, which is relevant to disease progression within the oxygen-restricted 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.

Outer membrane antigens of the uropathogen Proteus mirabilis recognized by the humoral response during experimental murine urinary tract infection

Proteus mirabilis, a gram-negative bacterium, is a frequent cause of complicated urinary tract infections in those with functional or anatomical abnormalities or those subject to long-term catheterization. To systematically identify surface-exposed antigens as potential vaccine candidates, proteins in the outer membrane fraction of bacteria were separated by two-dimensional gel electrophoresis and subjected to Western blotting with sera from mice experimentally infected with P. mirabilis. Protein spots reactive with sera were identified by mass spectrometry, which in conjunction with the newly completed genome sequence of P. mirabilis HI4320, was used to identify surface-exposed antigens. Culture conditions that may mimic in vivo conditions more closely than Luria broth (growth in human urine and under iron limitation and osmotic stress) were also used. Thirty-seven antigens to which a humoral response had been mounted, including 23 outer membrane proteins, were identified. These antigens are presumably expressed during urinary tract infection. Protein targets that are both actively required for virulence and antigenic may serve as protective antigens for vaccination; thus, five representative antigens were selected for use in virulence studies. Strains of P. mirabilis with mutations in three of the corresponding genes (the PMI0047 gene, rafY, and fadL) were not attenuated in the murine model of urinary tract infection. Putative iron acquisition proteins PMI0842 and PMI2596, however, both contribute to fitness in the urinary tract and thus emerge as vaccine candidates.

Identification and characterization of gonococcal iron transport systems as potential vaccine antigens

Gonorrhea is the second most commonly reported infectious disease in the USA, and incidence has been increasing in recent years. Antibiotic resistance among clinical isolates has reached a critical point at which the CDC currently recommends only a single class of antibiotic for treatment. These developments have hastened the search for a vaccine to protect against gonococcal infections. Vaccine efforts have been thwarted by the ability of the gonococcus to antigenically vary most surface structures. The transferrin-iron transport system is not subject to high-frequency phase or antigenic variation and is expressed by all pathogenic Neisseria. Vaccine formulations comprised of epitopes of the transferrin-binding proteins complexed with inactivated cholera toxin generated antibodies with potentially protective characteristics. These antigens, and others predicted from genome sequence data, could be developed into a vaccine that protects against neisserial infections.

Complete genome sequence of uropathogenic Proteus mirabilis, a master of both adherence and motility

The gram-negative enteric bacterium Proteus mirabilis is a frequent cause of urinary tract infections in individuals with long-term indwelling catheters or with complicated urinary tracts (e.g., due to spinal cord injury or anatomic abnormality). P. mirabilis bacteriuria may lead to acute pyelonephritis, fever, and bacteremia. Most notoriously, this pathogen uses urease to catalyze the formation of kidney and bladder stones or to encrust or obstruct indwelling urinary catheters. Here we report the complete genome sequence of P. mirabilis HI4320, a representative strain cultured in our laboratory from the urine of a nursing home patient with a long-term (> or =30 days) indwelling urinary catheter. The genome is 4.063 Mb long and has a G+C content of 38.88%. There is a single plasmid consisting of 36,289 nucleotides. Annotation of the genome identified 3,685 coding sequences and seven rRNA loci. Analysis of the sequence confirmed the presence of previously identified virulence determinants, as well as a contiguous 54-kb flagellar regulon and 17 types of fimbriae. Genes encoding a potential type III secretion system were identified on a low-G+C-content genomic island containing 24 intact genes that appear to encode all components necessary to assemble a type III secretion system needle complex. In addition, the P. mirabilis HI4320 genome possesses four tandem copies of the zapE metalloprotease gene, genes encoding six putative autotransporters, an extension of the atf fimbrial operon to six genes, including an mrpJ homolog, and genes encoding at least five iron uptake mechanisms, two potential type IV secretion systems, and 16 two-component regulators.

Multiple genes repress motility in uropathogenic Escherichia coli constitutively expressing type 1 fimbriae

Two surface organelles of uropathogenic Escherichia coli (UPEC), flagella and type 1 fimbriae, are critical for colonization of the urinary tract but mediate opposite actions. Flagella propel bacteria through urine and along mucus layers, while type 1 fimbriae allow bacteria to adhere to specific receptors present on uroepithelial cells. Constitutive expression of type 1 fimbriae leads to repression of motility and chemotaxis in UPEC strain CFT073, suggesting that UPEC may coordinately regulate motility and adherence. To identify genes involved in this regulation of motility by type 1 fimbriae, transposon mutagenesis was performed on a phase-locked type 1 fimbrial ON variant of strain CFT073 (CFT073 fim L-ON), followed by a screen for restoration of motility in soft agar. Functions of the genes identified included attachment, metabolism, transport, DNA mismatch repair, and transcriptional regulation, and a number of genes had hypothetical function. Isogenic deletion mutants of these genes were also constructed in CFT073 fim L-ON. Motility was partially restored in six of these mutants, including complementable mutations in four genes encoding known transcriptional regulators, lrhA, lrp, slyA, and papX; a mismatch repair gene, mutS; and one hypothetical gene, ydiV. Type 1 fimbrial expression in these mutants was unaltered, and the majority of these mutants expressed larger amounts of flagellin than the fim L-ON parental strain. Our results indicate that repression of motility in CFT073 fim L-ON is not solely due to the constitutive expression of type 1 fimbriae on the surfaces of the bacteria and that multiple genes may contribute to this repression.

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.

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

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

The phosphate regulon and bacterial virulence: a regulatory network connecting phosphate homeostasis and pathogenesis

Bacterial pathogens regulate virulence factor gene expression coordinately in response to environmental stimuli, including nutrient starvation. The phosphate (Pho) regulon plays a key role in phosphate homeostasis. It is controlled by the PhoR/PhoB two-component regulatory system. PhoR is an integral membrane signaling histidine kinase that, through an interaction with the ABC-type phosphate-specific transport (Pst) system and a protein called PhoU, somehow senses environmental inorganic phosphate (P(i)) levels. Under conditions of P(i) limitation (or in the absence of a Pst component or PhoU), PhoR activates its partner response regulator PhoB by phosphorylation, which, in turn, up- or down-regulates target genes. Single-cell profiling of PhoB activation has shown recently that Pho regulon gene expression exhibits a stochastic, "all-or-none" behavior. Recent studies have also shown that the Pho regulon plays a role in the virulence of several bacteria. Here, we present a comprehensive overview of the role of the Pho regulon in bacterial virulence. The Pho regulon is clearly not a simple regulatory circuit for controlling phosphate homeostasis; it is part of a complex network important for both bacterial virulence and stress response.

The high-affinity phosphate transporter Pst is a virulence factor for Proteus mirabilis during complicated urinary tract infection

Proteus mirabilis is a ubiquitous bacterium associated with complicated urinary tract infection (UTI). Mutagenesis studies of the wild-type strain HI4320 in the CBA mouse model of ascending UTIs have identified attenuated mutants with transposon insertions in genes encoding the high-affinity phosphate transporter Pst (pstS, pstA). The transcription of the pst operon (pstSCAB-phoU) and other members of the phosphate regulon of Escherichia coli, including alkaline phosphatase (AP), are regulated by the two-component regulatory system PhoBR and are repressed until times of phosphate starvation. This normal suppression was relieved in pstS::Tn5 and pstA::Tn5 mutants, which constitutively produced AP regardless of growth conditions. No significant growth defects were observed in vitro for the pst mutants during the independent culture or coculture studies in rich broth, phosphate-limiting minimal salts medium, or human urine. Mutants complemented with the complete pst operon repressed AP synthesis in vitro and colonized the mouse bladder in numbers comparable to the wild-type strain HI4320. Therefore, the Pst transport system imparts a significant in vivo advantage to wild-type P. mirabilis that is not required for in vitro growth. Thus, the Pst transporter has satisfied molecular Koch's postulates as a virulence factor in the pathogenesis of urinary tract infection caused by P. mirabilis.

Signature-tagged mutagenesis of Edwardsiella ictaluri identifies virulence-related genes, including a salmonella pathogenicity island 2 class of type III secretion systems

Edwardsiella ictaluri is the leading cause of mortality in channel catfish culture, but little is known about its pathogenesis. The use of signature-tagged mutagenesis in a waterborne infection model resulted in the identification of 50 mutants that were unable to infect/survive in catfish. Nineteen had minitransposon insertions in miscellaneous genes in the chromosome, 10 were in genes that matched to hypothetical proteins, and 13 were in genes that had no significant matches in the NCBI databases. Eight insertions were in genes encoding proteins associated with virulence in other pathogens, including three in genes involved in lipopolysaccharide biosynthesis, three in genes involved in type III secretion systems (TTSS), and two in genes involved in urease activity. With the use of a sequence from a lambda clone carrying several TTSS genes, Blastn analysis of the partially completed E. ictaluri genome identified a 26,135-bp pathogenicity island containing 33 genes of a TTSS with similarity to the Salmonella pathogenicity island 2 class of TTSS. The characterization of a TTSS apparatus mutant indicated that it retained its ability to invade catfish cell lines and macrophages but was defective in intracellular replication. The mutant also invaded catfish tissues in numbers equal to those of invading wild-type E. ictaluri bacteria but replicated poorly and was slowly cleared from the tissues, while the wild type increased in number.

Flagella allow uropathogenic Escherichia coli ascension into murine kidneys

Uropathogenic Escherichia coli (UPEC) cause bladder and kidney infections in humans and mice. UPEC initiate many kidney infections by ascending out of infected bladders, but how this occurs is not well understood. To determine if the flagella were responsible for the ascension of UPEC to the kidneys, a fliC mutation in strain NU149 was created. The fliC mutant spread poorly on soft agar plates, and 12h post-inoculation of murine urinary tracts, ascension into the murine kidneys was compromised in this mutant strain compared with wild-type bacteria. Complementation of the mutation restored the ability to spread on soft agar plates and ascend into the murine kidneys. To confirm the fliC mutant results, an anti-flagella monoclonal antibody that has been previously described inhibited the spread of UPEC strain NU149 on soft agar plates. When the anti-flagella antibody was mixed with strain NU149 cells and the antibody-treated bacterial cells were used to infect mice, significantly fewer mice had kidney infections than mice that were injected with strain NU149 cells mixed with normal mouse serum or anti-type 1 pili antibody. These results suggest that E. coli flagella may be of importance in allowing the bacteria to ascend from the bladder and initiate kidney infections in humans, and the use of an antibody against the flagella could prevent the spread of UPEC into the kidneys.

mini-Tn7 insertion in bacteria with secondary, non-glmS-linked attTn7 sites: example Proteus mirabilis HI4320

We previously constructed a series of mini-Tn7 chromosome integration vectors that, when provided only with the site-specific transposition machinery, generally transpose to a naturally evolved, neutral attTn7 site that is located 25-bp downstream of the glmS gene. Here we provide a protocol for application of the mini-Tn7 system in Proteus mirabilis as an example of a bacterium with a secondary attTn7 site that is not linked to glmS but, in this case, located in the carAB operon. The procedure involves, first, cloning of the genes of interest into an appropriate mini-Tn7 vector; second, co-transfer of the recombinant mini-Tn7 vector and a helper plasmid encoding the Tn7 site-specific transposition pathway into P. mirabilis by transformation, followed by selection of insertion-containing strains; third, PCR verification of mini-Tn7 insertions; and last, optional Flp-mediated excision of the antibiotic-resistance selection marker present on the chromosomally integrated mini-Tn7 element. When transposon-containing cells are selected on rich medium, insertions occur at both attTn7 sites with equal efficiency and frequency. Because carA mutants are arginine and pyrimidine auxotrophs, single-site insertions at the glmS attTn7 sites can be obtained by selection on minimal medium. From start to verification of the insertion events, the whole procedure takes 5 d. This chromosome integration system in P. mirabilis provides an important tool for animal and biofilm studies based on this bacterium. Vectors are available for gene complementation and expression, gene fusion analyses and tagging with a green fluorescent protein (GFP)-encoding reporter gene.

The oxidoreductase DsbA plays a key role in the ability of the Crohn's disease-associated adherent-invasive Escherichia coli strain LF82 to resist macrophage killing

Adherent-invasive Escherichia coli (AIEC) isolated from Crohn's disease patients is able to adhere to and invade intestinal epithelial cells and to replicate in mature phagolysosomes within macrophages. Here, we show that the dsbA gene, encoding a periplasmic oxidoreductase, was required for AIEC strain LF82 to adhere to intestinal epithelial cells and to survive within macrophages. The LF82-DeltadsbA mutant did not express flagella and, probably as a consequence of this, did not express type 1 pili. The role of DsbA in adhesion is restricted to the loss of flagella and type 1 pili, as forced contact between bacteria and cells and induced expression of type 1 pili restored the wild-type phenotype. In contrast, the dsbA gene is essential for AIEC LF82 bacteria to survive within macrophages, irrespective of the loss of flagella and type 1 pilus expression, and the survival ability of LF82-DeltadsbA was as low as that of the nonpathogenic E. coli K-12, which was efficiently killed by macrophages. We also provide evidence that the dsbA gene is needed for LF82 bacteria to grow and survive in an acidic and nutrient-poor medium that partly mimics the harsh environment of the phagocytic vacuole. In addition, under such stress conditions dsbA transcription is highly up-regulated. Finally, the CpxRA signaling pathway does not play a role in regulation of dsbA expression in AIEC LF82 bacteria under conditions similar to those of mature phagolysosomes.

Inhibition of swarming and virulence factor expression in Proteus mirabilis by resveratrol

Resveratrol (3,5,4-trihydroxy-trans-stilbene) is a phytoalexin compound with anti-inflammatory and antioxidant activities. The effect of resveratrol on swarming and virulence factor expression of Proteus mirabilis, an important pathogen infecting the urinary tract, was determined on swarming agar plates with and without the compound. Bacteria harvested at different times were assayed for cell length and the production of flagella, haemolysin and urease. Resveratrol inhibited P. mirabilis swarming and virulence factor expression in a dose-dependent manner. Resveratrol significantly inhibited swarming at 15 microg ml(-1), and completely inhibited swarming at 60 microg ml(-1). Inhibition of swarming and virulence factor expression was mediated through RsbA, a His-containing phosphotransmitter of the bacterial two-component signalling system possibly involved in quorum sensing. Complementation of an rsbA-defective mutant with the rsbA gene restored its responsiveness to resveratrol. The compound also inhibited the ability of P. mirabilis to invade human urothelial cells. These findings suggest that resveratrol has potential to be developed as an antimicrobial agent against P. mirabilis infection.

Targeting virulence for antibacterial chemotherapy: identifying and characterising virulence factors for lead discovery

The antibacterial drug discovery industry is fast losing participants; at the same time it is facing the challenge of developing new antibiotics that are effective against frequently occurring and multiply resistant organisms. One intriguing approach is to target bacterial virulence, and the last decade or so has seen a focus on bacterial pathogenesis along with the development of reagents and strategies that could make this possible. Several processes utilised by a range of bacteria to cause infection may be conserved enough to make attractive targets; indeed it is known that mammalian cells can affect bacterial gene expression and vice versa. Interesting targets involving virulence include type III secretion systems, two-component signal transduction systems, quorum sensing, and biofilm formation. In order to better understand these systems and strategies, investigators have developed novel strategies of their own, involving negative selections, surrogate models of infection, and screens for gene induction and antigenicity. Inhibitors of such targets would be unlikely to adversely affect patients, be cross-resistant to existing therapies, or cause resistance themselves. It might be the case that virulence target-based therapies would not be powerful enough to clear an existing infection alone, but if they are instead considered as adjunct therapy to existing antibiotics, or potentiators of the host immune response, they may show efficacy in a non-traditional way.

Signature-tagged mutagenesis of Klebsiella pneumoniae to identify genes that influence biofilm formation on extracellular matrix material

Klebsiella pneumoniae causes urinary tract infections, respiratory tract infections, and septicemia in susceptible individuals. Strains of Klebsiella frequently produce extended-spectrum beta-lactamases, and infections with these strains can lead to relatively high mortality rates (approximately 15%). Other virulence factors include production of an antiphagocytic capsule and outer membrane lipopolysaccharide (LPS), which mediates serum resistance, as well as fimbriae on the surface of the bacteria. Type 1 fimbriae mediate adherence to many types of epithelial cells and may facilitate adherence of the bacteria to the bladder epithelium. Type 3 fimbriae can bind in vitro to the extracellular matrix of urinary and respiratory tissues, suggesting that they mediate binding to damaged epithelial surfaces. In addition, type 3 fimbriae are required for biofilm formation by Klebsiella pneumoniae on plastics and human extracellular matrix; thus, they may facilitate the formation of treatment-resistant biofilm on indwelling plastic devices, such as catheters and endotracheal tubing. The presence of these devices may cause tissue damage, allowing Klebsiella to grow as a biofilm on exposed tissue basement membrane components. Though in vivo biofilm growth may be an important step in the infection process, little is known about the genetic factors required for biofilm formation by Klebsiella pneumoniae. Thus, we performed signature-tagged mutagenesis to identify factors produced by K. pneumoniae strain 43816 that are required for biofilm formation. We identified mutations in the cps capsule gene cluster, previously unidentified transcriptional regulators, fimbrial, and sugar phosphotransferase homologues, as well as genetic loci of unknown function, that affect biofilm formation.

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.

Breaching the great wall: peptidoglycan and microbial interactions

Once thought to be a process that occurred only in a few human pathogens, release of biologically active peptidoglycan fragments during growth by Gram-negative bacteria controls many types of bacterial interaction, including symbioses and interactions between microorganisms. This Perspective explores the role of peptidoglycan fragments in mediating a range of microbial-host interactions, and discusses the many systems in which peptidoglycan fragments released during bacterial growth might be active.

Seeking completeness in bacterial mutant hunts

The identification of most or all of the genetic functions that are required for a particular biological process could be achieved through phenotypic studies of high genome-coverage mutant collections. Technologies for creating such collections, in the form of mixed populations or individually arrayed sequence-defined mutants, are now available for numerous bacterial species. The analysis of mixed mutant collections using microarray-based detection procedures appears to be particularly effective in identifying functions required for complex processes such as virulence. The phenotypic analysis of sequence-defined mutant libraries provides a virtually complete identification of nonessential genes required for processes for which suitable screens can be devised. Such libraries also serve as a source of individual mutants for examining the biological relevance of gene associations revealed by transcriptional profiling or homology.

PhoU enhances the ability of extraintestinal pathogenic Escherichia coli strain CFT073 to colonize the murine urinary tract

The phoU gene is the last cistron in the pstSCAB-phoU operon and functions as a negative regulator of the Pho regulon. The authors previously identified a phoU mutant of extraintestinal pathogenic Escherichia coli strain CFT073 and demonstrated that this mutant was attenuated for survival in the murine model of ascending urinary tract infection. It is hypothesized that the PhoU protein might serve as a urovirulence factor by indirectly affecting the expression of virulence-related genes. In this study, the phoU mutant was further characterized and PhoU was confirmed as a virulence factor. Western blot analysis demonstrated that insertion of the transposon in the phoU gene disrupted the expression of PhoU. The phoU mutant had derepressed alkaline phosphatase activity under phosphate-excess and -limiting conditions. In single-challenge murine ascending urinary tract infection experiments, quantitative cultures of urine, bladder and kidney revealed no significant differences between the phoU mutant strain and the wild-type strain CFT073. However, in competitive colonization experiments, the phoU mutant strain was significantly out-competed by the wild-type strain in the kidneys and urine and recovered in lower amount in the bladder. Complementation of the phoU mutant with a plasmid containing the wild-type phoU gene restored the expression of PhoU and alkaline phosphate activity to wild-type levels and no significant difference in colonization was observed between the phoU mutant containing the complementing plasmid and wild-type in competitive colonization experiments. In human urine, the phoU mutant and wild-type grew comparably when inoculated independently, indicating that the attenuation observed was not due to a general growth defect. However, as observed in vivo, the wild-type out-competed the phoU mutant in competition growth experiments in human urine. These data indicate that PhoU contributes to efficient colonization of the murine urinary tract and add PhoU to a short list of confirmed urovirulence factors.

Urease produced by Coccidioides posadasii contributes to the virulence of this respiratory pathogen

Urease activity during in vitro growth in the saprobic and parasitic phases of Coccidioides spp. is partly responsible for production of intracellular ammonia released into the culture media and contributes to alkalinity of the external microenvironment. Although the amino acid sequence of the urease of Coccidioides posadasii lacks a predicted signal peptide, the protein is transported from the cytosol into vesicles and the central vacuole of parasitic cells (spherules). Enzymatically active urease is released from the contents of mature spherules during the parasitic cycle endosporulation stage. The endospores, together with the urease and additional material which escape from the ruptured parasitic cells, elicit an intense host inflammatory response. Ammonia production by the spherules of C. posadasii is markedly increased by the availability of exogenous urea found in relatively high concentrations at sites of coccidioidal infection in the lungs of mice. Direct measurement of the pH at these infection sites revealed an alkaline microenvironment. Disruption of the urease gene of C. posadasii resulted in a marked reduction in the amount of ammonia secreted in vitro by the fungal cells. BALB/c mice challenged intranasally with the mutant strain showed increased survival, a well-organized granulomatous response to infection, and better clearance of the pathogen than animals challenged with either the parental or the reconstituted (revertant) strain. We conclude that ammonia and enzymatically active urease released from spherules during the parasitic cycle of C. posadasii contribute to host tissue damage, which exacerbates the severity of coccidioidal infection and enhances the virulence of this human respiratory pathogen.

Signature-tagged mutagenesis: technical advances in a negative selection method for virulence gene identification

Signature-tagged mutagenesis (STM) is a powerful negative selection method, predominantly used to identify the genes of a pathogen that are required for the successful colonization of an animal host. Since its first description a decade ago, STM has been applied to screen a vast amount of transposon insertion mutants in 31 bacterial species. This has led to the identification of over 1,700 bacterial genes that are involved in virulence. Despite the preservation of the basic design, the STM method has been developed further owing to recent advances including different designs of the signature-tags and profound changes in the mode of detection. These advances promoted substantially the application range and versatility of the STM method.

Uropathogenic Escherichia coli flagella aid in efficient urinary tract colonization

In the murine model of urinary tract infections (UTI), cystitis by uropathogenic Escherichia coli (UPEC) occurs through an intimate relationship with the bladder superficial umbrella cell entailing cycles of adherence, invasion, intracellular bacterial community (IBC) formation, and dispersal (fluxing) from the intracellular environment. IBC dispersal is a key step that results in the spread of bacteria over the epithelial surface to initiate additional rounds of IBC formation. We investigated the role of flagella in mediating adherence and motility during UTI, hypothesizing that the dispersion of the IBC would be incomplete in the absence of motility, thus interrupting the IBC pathway and attenuating the infection. Using gfp reporter fusions, the expression of the flagellar class I flhDC and class III fliC genes was monitored to track key points of regulation throughout the pathogenic cascade. In vitro, growth under conditions promoting motility resulted in the robust expression of both fusions. In contrast, only the class I fusion produced significant expression throughout early stages of IBC development including the dispersion stage. Thus, unlike in vitro modeling of motility, the regulatory cascade appeared incomplete in vivo. Throughout IBC formation, nonmotile DeltafliC mutants achieved the same number of IBCs as the wild-type (wt) strain, demonstrating that flagella are neither essential nor required for first- or second-generation IBC formation. However, in competition experiments between wt and DeltafliC strains, the wt was shown to have a fitness advantage in persisting throughout the urinary tract for 2 weeks, demonstrating a subtle but measurable role for flagella in virulence.

Identification of virulence determinants for endocarditis in Streptococcus sanguinis by signature-tagged mutagenesis

Streptococcus sanguinis is a gram-positive, facultative anaerobe and a normal inhabitant of the human oral cavity. It is also one of the most common agents of infective endocarditis, a serious endovascular infection. To identify virulence factors for infective endocarditis, signature-tagged mutagenesis (STM) was applied to the SK36 strain of S. sanguinis, whose genome is being sequenced. STM allows the large-scale creation, in vivo screening, and recovery of a series of mutants with altered virulence. Screening of 800 mutants by STM identified 38 putative avirulent and 5 putative hypervirulent mutants. Subsequent molecular analysis of a subset of these mutants identified genes encoding undecaprenol kinase, homoserine kinase, anaerobic ribonucleotide reductase, adenylosuccinate lyase, and a hypothetical protein. Virulence reductions ranging from 2-to 150-fold were confirmed by competitive index assays. One putatively hypervirulent strain with a transposon insertion in an intergenic region was identified, though increased virulence was not confirmed in competitive index assays. All mutants grew comparably to SK36 in aerobic broth culture except for the homoserine kinase mutant. Growth of this mutant was restored by the addition of threonine to the medium. Mutants containing an insertion or in-frame deletion in the anaerobic ribonucleotide reductase gene failed to grow under strictly anaerobic conditions. The results suggest that housekeeping functions such as cell wall synthesis, amino acid and nucleic acid synthesis, and the ability to survive under anaerobic conditions are important virulence factors in S. sanguinis endocarditis.

Staphylococcus aureus DsbA is a membrane-bound lipoprotein with thiol-disulfide oxidoreductase activity

DsbA proteins, the primary catalysts of protein disulfide bond formation, are known to affect virulence and penicillin resistance in Gram-negative bacteria. We identified a putative DsbA homologue in the Gram-positive pathogen Staphylococcus aureus that was able to restore the motility phenotype of an Escherichia coli dsbA mutant and thus demonstrated a functional thiol oxidoreductase activity. The staphylococcal DsbA (SaDsbA) had a strong oxidative redox potential of -131 mV. The persistence of the protein throughout the growth cycle despite its predominant transcription during exponential growth phase suggested a rather long half-life for the SaDsbA. SaDsbA was found to be a membrane localised lipoprotein, supporting a role in disulfide bond formation. But so far, neither in vitro nor in vivo phenotype could be identified in a staphylococcal dsbA mutant, leaving its physiological role unknown. The inability of SaDsbA to interact with the E. coli DsbB and the lack of an apparent staphylococcal DsbB homologue suggest an alternative re-oxidation pathway for the SaDsbA.

Going against the grain: chemotaxis and infection in Vibrio cholerae

Chemotaxis is the process by which motile cells move in a biased manner both towards favourable and away from unfavourable environments. The requirement of this process for infection has been examined in several bacterial pathogens, including Vibrio cholerae. The single polar flagellum of Vibrio species is powered by a sodium-motive force across the inner membrane, and can rotate to produce speeds of up to 60 cell-body lengths (approximately 60microm) per second. Investigating the role of the chemotactic control of rapid flagellar motility during V. cholerae infection has revealed some unexpected and intriguing results.

Whole genome sequence of Staphylococcus saprophyticus reveals the pathogenesis of uncomplicated urinary tract infection

Staphylococcus saprophyticus is a uropathogenic Staphylococcus frequently isolated from young female outpatients presenting with uncomplicated urinary tract infections. We sequenced the whole genome of S. saprophyticus type strain ATCC 15305, which harbors a circular chromosome of 2,516,575 bp with 2,446 ORFs and two plasmids. Comparative genomic analyses with the strains of two other species, Staphylococcus aureus and Staphylococcus epidermidis, as well as experimental data, revealed the following characteristics of the S. saprophyticus genome. S. saprophyticus does not possess any virulence factors found in S. aureus, such as coagulase, enterotoxins, exoenzymes, and extracellular matrix-binding proteins, although it does have a remarkable paralog expansion of transport systems related to highly variable ion contents in the urinary environment. A further unique feature is that only a single ORF is predictable as a cell wall-anchored protein, and it shows positive hemagglutination and adherence to human bladder cell associated with initial colonization in the urinary tract. It also shows significantly high urease activity in S. saprophyticus. The uropathogenicity of S. saprophyticus can be attributed to its genome that is needed for its survival in the human urinary tract by means of novel cell wall-anchored adhesin and redundant uro-adaptive transport systems, together with urease.

Swarmer cell differentiation in Proteus mirabilis

Under the appropriate environmental conditions, the gram-negative bacterium Proteus mirabilis undergoes a remarkable differentiation to form a distinct cell type called a swarmer cell. The swarmer cell is characterized by a 20- to 40-fold increase in both cell length and the number of flagella per cell. Environmental conditions required for swarmer cell differentiation include: surface contact, inhibition of flagellar rotation, a sufficient cell density and cell-to-cell signalling. The differentiated swarmer cell is then able to carry out a highly ordered population migration termed swarming. Genetic analysis of the swarming process has revealed that a large variety of distinct loci are required for this differentiation including: genes involved in regulation, lipopolysaccharide and peptidoglycan synthesis, cell division, ATP production, putrescine biosynthesis, proteolysis and cell shape determination. The process of swarming is important medically because the expression of virulence genes and the ability to invade cells are coupled to the differentiated swarmer cell. In this review, the genetic and environmental requirements for swarmer cell differentiation will be outlined. In addition, the role of the differentiated swarmer cell in virulence and its possible role in biofilm formation will be discussed.

Interleukin-8 response in cells from the human urinary tract induced by lipopolysaccharides of Proteus mirabilis O3 and O18

PURPOSE

Proteus mirabilis is a common pathogen associated mainly with complicated urinary tract infections and sometimes with septicemia. There is great serological diversity of the microorganism. While P. mirabilis O3 is commonly found in patients with infections, the serotype O18 rarely occurs. The O18 lipopolysaccharide contains a phosphocholine substitute, which makes it unique among Proteus strains. To explain different clinical significance of the strains we evaluated the biological activity of the lipopolysaccharides of P. mirabilis O3 and O18, as measured by interleukin-8 (IL-8) production.

MATERIALS AND METHODS

Three cell lines were used, namely uroepithelial cells, renal epithelial cells and monocytes. IL-8 production was determined on the protein and mRNA levels using enzyme-linked immunosorbent assay and real-time polymerase chain reaction, respectively, and CD14 expression on the cell surface was studied using flow cytometry.

RESULTS

Uroepithelial cells and monocytes reacted to lipopolysaccharides by higher IL-8 production compared with renal epithelial cells. Cell specific IL-8 response corresponded to the cell expression of CD14. Renal epithelial cells produced more IL-8 after stimulation with the phosphocholine rich lipopolysaccharide O18, although adding phosphocholine alone did not induce or increase IL-8 production.

CONCLUSIONS

Our data suggest that different cells within the human urinary tract have different roles during urinary tract infection. The biological activity and pathogenicity of P. mirabilis lipopolysaccharides might be determined by their specific chemical structure.

An improved arbitrary primed PCR method for rapid characterization of transposon insertion sites

Modifications were made to published arbitrary primed polymerase chain reaction (AP-PCR) procedures that resulted in increased specificity and sensitivity. Several arbitrary primer sequences were also evaluated, resulting in recommendations for primer design.

The IrgA homologue adhesin Iha is an Escherichia coli virulence factor in murine urinary tract infection

The role of the Escherichia coli iron-regulated gene homologue adhesin (Iha) in the pathogenesis of urinary tract infections (UTIs) is unknown. We performed a series of complementary analyses to confirm or refute the hypothesis that Iha is a virulence factor in uropathogenic E. coli. Fecal E. coli isolates exhibited significantly lower prevalences of iha (range, 14 to 22%) than did clinical isolates from cases of pediatric cystitis or pyelonephritis, adult pyelonephritis or urosepsis, or bacteremia (range, 38 to 74%). Recombinant Iha from E. coli pyelonephritis isolate CFT073 conferred upon nonadherent E. coli ORN172 the ability to adhere to cultured T-24 human uroepithelial cells. In a well-established mouse model of ascending UTI, CFT073 and its derivative UPEC76 (a pap [P fimbriae] mutant version of strain CFT073) each significantly outcompeted their respective iha deletion mutants in CBA/J mice 48 h after bladder challenge (P < 0.03 for urine, both kidneys, and bladders of both constructs, except for bladders of mice challenged with UPEC76 and its deletion mutant, where P = 0.11). These data suggest that Iha(CFT073) is a virulence factor and might be a target for anti-UTI interventions.

The role of peptidoglycan in pathogenesis

Bacterial pathogens rely on a variety of virulence factors to establish the colonization of a new niche. Although peptidoglycan and its muropeptide derivatives have been known to possess potent biological properties, until recently the molecular bases were poorly understood. With the identification of the cytosolic surveillance mechanism mediated by the nucleotide-binding oligomerization domain (Nod)1 and Nod2 proteins, which detect unique peptidoglycan-derived muropeptides, these muropeptides should be considered as potential virulence factors. Recent research highlights the role of peptidoglycan in the pathogenesis of different human pathogens such as Streptococcus pneumoniae, Listeria monocytogenes or Helicobacter pylori.