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

Adherence and metal-ion acquisition gene expression increases during infection with Treponema phagedenis strains from bovine digital dermatitis

Digital dermatitis (DD) is an ulcerative foot lesion on the heel bulbs of dairy cattle. DD is a polymicrobial disease with no precise etiology, although Treponema spirochetes are found disproportionally abundant in diseased tissue. Within Treponema, several different species are found in DD; however, the species Treponema phagedenis is uniformly found in copious quantities and deep within the skin layers of the active, ulcerative stages of disease. The pathogenic mechanisms these bacteria use to persist in the skin and the precise role they play in the pathology of DD are widely unknown. To explore the pathogenesis and virulence of Treponema phagedenis, newly isolated strains of this species were investigated in a subcutaneous murine abscess model. In the first trial, a dosage study was conducted to compare the pathogenicity of different strains across three different treponemes per inoculum (TPI) doses based on abscess volumes. In the second trial, the expression levels of 11 putative virulence genes were obtained to gain insight into their involvement in pathogenesis. During the RT-qPCR analysis, it was determined that genes encoding for two metal-ion import lipoproteins and two adherence genes were found highly upregulated during infection. Conversely, two genes involved in motility and chemotaxis were found to not be significantly upregulated or utilized during infection. These results were supported by gene expression data from natural M2 lesions of dairy cattle. This gene expression analysis could highlight the preference in strategy for T. phagedenis to persist and adhere in the host rather than engage in motility and disseminate.

Disruption of Phosphate Homeostasis Sensitizes Staphylococcus aureus to Nutritional Immunity

To control infection, mammals actively withhold essential nutrients, including the transition metal manganese, by a process termed nutritional immunity. A critical component of this host response is the manganese-chelating protein calprotectin. While many bacterial mechanisms for overcoming nutritional immunity have been identified, the intersection between metal starvation and other essential inorganic nutrients has not been investigated. Here, we report that overexpression of an operon encoding a highly conserved inorganic phosphate importer, PstSCAB, increases the sensitivity of Staphylococcus aureus to calprotectin-mediated manganese sequestration. Further analysis revealed that overexpression of pstSCAB does not disrupt manganese acquisition or result in overaccumulation of phosphate by S. aureus However, it does reduce the ability of S. aureus to grow in phosphate-replete defined medium. Overexpression of pstSCAB does not aberrantly activate the phosphate-responsive two-component system PhoPR, nor was this two-component system required for sensitivity to manganese starvation. In a mouse model of systemic staphylococcal disease, a pstSCAB-overexpressing strain is significantly attenuated compared to wild-type S. aureus This defect is partially reversed in a calprotectin-deficient mouse, in which manganese is more readily available. Given that expression of pstSCAB is regulated by PhoPR, these findings suggest that overactivation of PhoPR would diminish the ability of S. aureus to resist nutritional immunity and cause infection. As PhoPR is also necessary for bacterial virulence, these findings imply that phosphate homeostasis represents a critical regulatory node whose activity must be precisely controlled in order for S. aureus and other pathogens to cause infection.

Virulence traits and pathogenicity of uropathogenic Escherichia coli isolates with common and uncommon O serotypes

Urinary tract infections (UTIs) are among the most common human diseases worldwide. This study aimed to collect uropathogenic Escherichia coli (UPEC) isolates from Jiangsu Province and obtain insights into the molecular epidemiology of UPEC in this region. The O serotypes, phylogenetic groups, and virulence factors of 183 UPEC isolates were determined. In this study, we isolated 51 UPEC isolates with common O serotypes including O1, O2, O4, O6, O7, O16, O18 and O75, as well as 35 of those with uncommonly encountered O serotypes including O8, O12, O15, O26, and O74. Groups B2 and D were the most prevalent phylogenetic groups and accounted for 29.5% and 41% of the isolates, respectively. In the tested 13 virulence genes (VGs), tonB and dsdA possessed the highest prevalence rate, followed by fimH, degP and ompR. Several other virulence genes such as fliC, neuC, ireA, and vat had prevalence less than 23%. Moreover, representative isolates belonging to common or uncommon O serotypes with different numbers of VGs were chosen for the pathogenic analyses. Based on the results of 1-day-old chick lethality assay and UTI ascending mouse infection model, our study suggested that the virulence of UPEC isolates for chicks and/or mice depended on both the number of VGs expressed and the O serotypes.

Environmental phosphate differentially affects virulence phenotypes of uropathogenic Escherichia coli isolates causative of prostatitis

K-12 Escherichia coli cells grown in static media containing a critical phosphate (Pi) concentration ≥25 mM maintained a high polyphosphate (polyP) level in stationary phase, impairing biofilm formation, a phenomenon that is triggered by polyP degradation. Pi concentration in human urine fluctuates according to health state. Here, the influence of environmental Pi concentration on the occurrence of virulence traits in uropathogenic E. coli (UPEC) isolated from acute prostatitis patients was evaluated. After a first screening, 3 isolates were selected according to differential biofilm formation profiles depending on media Pi concentration. For each isolate, biofilm positive and negative conditions were established. Regardless of the isolate, biofilm formation capacity was accompanied with curli and cellulose production and expression of some key virulence factors associated with adhesion. When the selected isolates were grown in their non-biofilm-forming condition, low concentrations of nalidixic acid and ciprofloxacin induced biofilm formation. Interestingly, similar to laboratory strains, polyP degradation induced biofilm formation in the selected isolates. Data demonstrated the complexity of UPEC responses to environmental Pi and the importance of polyP metabolism in the virulence of clinical isolates.

Persisters, persistent infections and the Yin-Yang model

Persisters are a small fraction of quiescent bacterial cells that survive lethal antibiotics or stresses but can regrow under appropriate conditions. Persisters underlie persistent and latent infections and post-treatment relapse, posing significant challenges for the treatment of many bacterial infections. The current definition of persisters has drawbacks, and a Yin–Yang model is proposed to describe the heterogeneous nature of persisters that have to be defined in highly specific conditions. Despite their discovery more than 70 years ago, the mechanisms of persisters are poorly understood. Recent studies have identified a number of genes and pathways that shed light on the mechanisms of persister formation or survival. These include toxin–antitoxin modules, stringent response, DNA repair or protection, phosphate metabolism, alternative energy production, efflux, anti-oxidative defense and macromolecule degradation. More sensitive single-cell techniques are required for a better understanding of persister mechanisms. Studies of bacterial persisters have parallels in other microbes (fungi, parasites, viruses) and cancer stem cells in terms of mechanisms and treatment approaches. New drugs and vaccines targeting persisters are critical for improved treatment of persistent infections and perhaps cancers. Novel treatment strategies for persisters and persistent infections are discussed.

Decreased expression of type 1 fimbriae by a pst mutant of uropathogenic Escherichia coli reduces urinary tract infection

The pstSCAB-phoU operon encodes the phosphate-specific transport system (Pst). Loss of Pst constitutively activates the Pho regulon and decreases bacterial virulence. However, specific mechanisms underlying decreased bacterial virulence through inactivation of Pst are poorly understood. In uropathogenic Escherichia coli (UPEC) strain CFT073, inactivation of pst decreased urinary tract colonization in CBA/J mice. The pst mutant was deficient in production of type 1 fimbriae and showed decreased expression of the fimA structural gene which correlated with differential expression of the fimB, fimE, ipuA, and ipbA genes, encoding recombinases, mediating inversion of the fim promoter. The role of fim downregulation in attenuation of the pst mutant was confirmed using a fim phase-locked-on derivative, which demonstrated a significant gain in virulence. In addition, the pst mutant was less able to invade human bladder epithelial cells. Since type 1 fimbriae contribute to UPEC virulence by promoting colonization and invasion of bladder cells, the reduced bladder colonization by the pst mutant is predominantly attributed to downregulation of these fimbriae. Elucidation of mechanisms mediating the control of type 1 fimbriae through activation of the Pho regulon in UPEC may open new avenues for therapeutics or prophylactics against urinary tract infections.

The Vibrio cholerae Pst2 phosphate transport system is upregulated in biofilms and contributes to biofilm-induced hyperinfectivity

Vibrio cholerae is the causative agent of the deadly diarrheal disease cholera. As part of its life cycle, V. cholerae persists in marine environments, where it forms surface-attached communities commonly described as biofilms. Evidence indicates that these biofilms constitute the infectious form of the pathogen during outbreaks. Previous work has shown that biofilm-derived V. cholerae cells, even when fully dispersed from the biofilm matrix, are vastly more infectious than planktonic (free-living) cells. Here, we sought to identify factors that contribute to biofilm-induced hyperinfectivity in V. cholerae, and we present evidence for one aspect of the molecular basis of this phenotype. We identified proteins upregulated during growth in biofilms and determined their contributions to the hyperinfectivity phenotype. We found that PstS2, the periplasmic component of the Pst2 phosphate uptake system, was enriched in biofilms. Another gene in the pst2 locus was transcriptionally upregulated in biofilms. Using the infant mouse model, we found that mutation of two pst2 components resulted in impaired colonization. Importantly, deletion of the Pst2 inner membrane complex caused a greater colonization defect after growth in a biofilm compared to shaking culture. Based on these data, we propose that V. cholerae cells in biofilms upregulate the Pst2 system and therefore gain an advantage upon entry into the host. Further characterization of factors contributing to biofilm-induced hyperinfectivity in V. cholerae will improve our understanding of the transmission of the bacteria from natural aquatic habitats to the human host.

Two-component PhoB-PhoR regulatory system and ferric uptake regulator sense phosphate and iron to control virulence genes in type III and VI secretion systems of Edwardsiella tarda

Inorganic phosphate (P(i)) and iron are essential nutrients that are depleted by vertebrates as a protective mechanism against bacterial infection. This depletion, however, is sensed by some pathogens as a signal to turn on the expression of virulence genes. Here, we show that the PhoB-PhoR two-component system senses changes in P(i) concentration, whereas the ferric uptake regulator (Fur) senses changes in iron concentration in Edwardsiella tarda PPD130/91 to regulate the expression of type III and VI secretion systems (T3SS and T6SS) through an E. tarda secretion regulator, EsrC. In sensing low P(i) concentration, PhoB-PhoR autoregulates and activates the phosphate-specific transport operon, pstSCAB-phoU, by binding directly to the Pho box in the promoters of phoB and pstS. PhoB also binds with EsrC simultaneously on the promoter of an E. tarda virulence protein, evpA, to regulate directly the transcription of genes from T6SS. In addition, PhoB requires and interacts with PhoU to activate esrC and suppress fur indirectly through unidentified regulators. Fur, on the other hand, senses high iron concentration and binds directly to the Fur box in the promoter of evpP to inhibit EsrC binding to the same region. In addition, Fur suppresses transcription of phoB, pstSCAB-phoU, and esrC indirectly via unidentified regulators, suggesting negative cross-talk with the Pho regulon. Physical interactions exist between Fur and PhoU and between Fur and EsrC. Our findings suggest that T3SS and T6SS may carry out distinct roles in the pathogenicity of E. tarda by responding to different environmental factors.

Increased Pho regulon activation correlates with decreased virulence of an avian pathogenic Escherichia coli O78 strain

Avian pathogenic Escherichia coli (APEC) strains are associated with respiratory infections, septicemia, cellulitis, peritonitis, and other conditions, since colibacillosis manifests in many ways. The Pho regulon is jointly controlled by the two-component regulatory system PhoBR and by the phosphate-specific transport (Pst) system. To determine the specific roles of the PhoBR regulon and the Pst system in the pathogenesis of the APEC O78 strain χ7122, different phoBR and pst mutant strains were tested in vivo in chickens and in vitro for virulence traits. Mutations resulting in constitutive activation of the Pho regulon rendered strains more sensitive than the wild type to hydrogen peroxide and to the bactericidal effects of rabbit serum. In addition, production of type 1 fimbriae was also impaired in these strains. Using a chicken competitive infection model, all PhoB constitutive mutants were outcompeted by the wild-type parent, including strains containing a functional Pst system. Cumulative inactivation of the Pst system and the PhoB regulator resulted in a restoration of virulence. In addition, loss of the PhoB regulator alone did not affect virulence in the chicken infection model. Interestingly, the level of attenuation of the mutant strains correlated directly with the level of activation of the Pho regulon. Overall, results indicate that activation of the Pho regulon rather than phosphate transport by the Pst system plays a major role in the attenuation of the APEC O78 strain χ7122.

Proteomic analysis of growth phase-dependent expression of Legionella pneumophila proteins which involves regulation of bacterial virulence traits

Legionella pneumophila, which is a causative pathogen of Legionnaires' disease, expresses its virulent traits in response to growth conditions. In particular, it is known to become virulent at a post-exponential phase in vitro culture. In this study, we performed a proteomic analysis of differences in expression between the exponential phase and post-exponential phase to identify candidates associated with L. pneumophila virulence using 2-Dimentional Fluorescence Difference Gel Electrophoresis (2D-DIGE) combined with Matrix-Assisted Laser Desorption/Ionization–Mass Spectrometry (MALDI-TOF-MS). Of 68 identified proteins that significantly differed in expression between the two growth phases, 64 were up-regulated at a post-exponential phase. The up-regulated proteins included enzymes related to glycolysis, ketone body biogenesis and poly-3-hydroxybutyrate (PHB) biogenesis, suggesting that L. pneumophila may utilize sugars and lipids as energy sources, when amino acids become scarce. Proteins related to motility (flagella components and twitching motility-associated proteins) were also up-regulated, predicting that they enhance infectivity of the bacteria in host cells under certain conditions. Furthermore, 9 up-regulated proteins of unknown function were found. Two of them were identified as novel bacterial factors associated with hemolysis of sheep red blood cells (SRBCs). Another 2 were found to be translocated into macrophages via the Icm/Dot type IV secretion apparatus as effector candidates in a reporter assay with Bordetella pertussis adenylate cyclase. The study will be helpful for virulent analysis of L. pneumophila from the viewpoint of physiological or metabolic modulation dependent on growth phase.

Transcriptional profiling of Actinobacillus pleuropneumoniae during the acute phase of a natural infection in pigs

Background

Actinobacillus pleuropneumoniae is the etiological agent of porcine pleuropneumonia, a respiratory disease which causes great economic losses worldwide. Many virulence factors are involved in the pathogenesis, namely capsular polysaccharides, RTX toxins, LPS and many iron acquisition systems. In order to identify genes that are expressed in vivo during a natural infection, we undertook transcript profiling experiments with an A. pleuropneumoniae DNA microarray, after recovery of bacterial mRNAs from serotype 5b-infected porcine lungs. AppChip2 contains 2033 PCR amplicons based on the genomic sequence of App serotype 5b strain L20, representing more than 95% of ORFs greater than 160 bp in length.

Results

Transcriptional profiling of A. pleuropneumoniae recovered from the lung of a pig suffering from a natural infection or following growth of the bacterial isolate in BHI medium was performed. An RNA extraction protocol combining beadbeating and hot-acid-phenol was developed in order to maximize bacterial mRNA yields and quality following total RNA extraction from lung lesions. Nearly all A. pleuropneumoniae transcripts could be detected on our microarrays, and 150 genes were deemed differentially expressed in vivo during the acute phase of the infection. Our results indicate that, for example, gene apxIVA from an operon coding for RTX toxin ApxIV is highly up-regulated in vivo, and that two genes from the operon coding for type IV fimbriae (APL_0878 and APL_0879) were also up-regulated. These transcriptional profiling data, combined with previous comparative genomic hybridizations performed by our group, revealed that 66 out of the 72 up-regulated genes are conserved amongst all serotypes and that 3 of them code for products that are predicted outer membrane proteins (genes irp and APL_0959, predicted to code for a TonB-dependent receptor and a filamentous hemagglutinin/adhesin respectively) or lipoproteins (gene APL_0920). Only 4 of 72 up-regulated genes had previously been identified in controled experimental infections.

Conclusions

These genes that we have identified as up-regulated in vivo, conserved across serotypes and coding for potential outer membrane proteins represent potential candidates for the development of a cross-protective vaccine against porcine pleuropneumonia.

Overexpression of outer membrane protein OprT and increase of membrane permeability in phoU mutant of toluene-tolerant bacterium Pseudomonas putida GM730

Eight toluene-sensitive mutants were previously isolated from the toluene-tolerant bacterium Pseudomonas putida GM730. One of these mutants was TOS6, in which Tn5 had been inserted into phoU. Susceptibility to multiple antibiotics, as well as toluene sensitivity, was increased in the phoU mutant of P. putida GM730. We compared the outer membrane proteins from the phoU mutant and wild-type via two-dimensional gel electrophoresis. A 45 kDa protein was dramatically overexpressed as the result of phoU inactivation, and this protein was identified by peptide mass fingerprinting and microsequencing as a conserved hypothetical protein consisting of 414 amino acids. The protein, designated as OprT, harbors a signal sequence and extended beta-sheets, both of which are features common to the bacterial porins. The rate of ethidium bromide accumulation in TOS6 was higher than in GM730, which indicates that the TOS6 membranes may be more permeable to ethidium bromide than are the membranes of GM730. We propose that the toluene sensitivity and increased antibiotic susceptibility observed in the phoU mutant may be attributable to increased membrane permeability.

Uropathogenic Escherichia coli

The urinary tract is among the most common sites of bacterial infection, and Escherichia coli is by far the most common species infecting this site. Individuals at high risk for symptomatic urinary tract infection (UTI) include neonates, preschool girls, sexually active women, and elderly women and men. E. coli that cause the majority of UTIs are thought to represent only a subset of the strains that colonize the colon. E. coli strains that cause UTIs are termed uropathogenic E. coli (UPEC). In general, UPEC strains differ from commensal E. coli strains in that the former possess extragenetic material, often on pathogenicity-associated islands (PAIs), which code for gene products that may contribute to bacterial pathogenesis. Some of these genes allow UPEC to express determinants that are proposed to play roles in disease. These factors include hemolysins, secreted proteins, specific lipopolysaccharide and capsule types, iron acquisition systems, and fimbrial adhesions. The current dogma of bacterial pathogenesis identifies adherence, colonization, avoidance of host defenses, and damage to host tissues as events vital for achieving bacterial virulence. These considerations, along with analysis of the E. coli CFT073, UTI89, and 536 genomes and efforts to identify novel virulence genes should advance the field significantly and allow for the development of a comprehensive model of pathogenesis for uropathogenic E. coli.Further study of the adaptive immune response to UTI will be especially critical to refine our understanding and treatment of recurrent infections and to develop vaccines.

Role of the K2 capsule in Escherichia coli urinary tract infection and serum resistance

BACKGROUND

Capsule expression may be important during ascending Escherichia coli urinary tract infections (UTIs).

METHODS

An isogenic ksl(k2)ABCDE mutant of extraintestinal pathogenic E. coli (ExPEC) strain CFT073 that could not synthesize the K2 capsule was compared with wild-type CFT073, to determine virulence in a murine model of ascending UTI and in vitro killing assays.

RESULTS

No significant differences were observed regarding the abilities of the mutant and the wild-type CFT073 strains to colonize the murine urinary tract in single-challenge infection experiments. However, in competitive-colonization experiments, the mutant was significantly outcompeted by the wild-type strain in urine and the kidneys. The mutant strain was also more susceptible to human serum. Complementation of the mutant with a plasmid containing the ksl(k2)ABCDE genes restored capsule expression, enhanced survival in the murine urinary tract, and restored serum resistance.

CONCLUSION

These results indicate that expression of the K2 capsule is important for the pathogenesis of UTI and provides protection against complement-mediated killing. To our knowledge, this is the first study in which the E. coli capsule has been proven to play a role in infection by use of isogenic mutants and genetic complementation.

Survival of uropathogenic Escherichia coli in the murine urinary tract is dependent on OmpR

Uropathogenic Escherichia coli (UPEC) can grow in environments with significantly elevated osmolarities, such as murine and human urinary tracts. OmpR is the response regulator part of a two-component OmpR-EnvZ regulatory system that responds to osmotic stresses. To determine the role of OmpR in UPEC survival, a DeltaompR mutant was created in the UPEC clinical isolate NU149. The DeltaompR mutant had a growth defect compared with the wild-type strain under osmotic stress conditions; this defect was complemented by the full-length ompR gene on a plasmid, but not with a mutant OmpR with an alanine substitution for aspartic acid at the phosphorylation site at position 55. Furthermore, the DeltaompR mutant displayed up to 2-log reduction in bacterial cell numbers in murine bladders and kidneys compared with wild-type bacteria after 5 days of infection. The ability of the bacteria to survive was restored to wild-type levels when the DeltaompR mutant strain was complemented with wild-type ompR, but not when the alanine-substituted ompR gene was used. This study has fulfilled molecular Koch's postulates by showing the pivotal role OmpR plays in UPEC survival within the murine urinary tract.

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.

Genome-wide transcriptional response of an avian pathogenic Escherichia coli (APEC) pst mutant

Background

Avian pathogenic E. coli (APEC) are associated with extraintestinal diseases in poultry. The pstSCAB-phoU operon belongs to the Pho regulon and encodes the phosphate specific transport (Pst) system. A functional Pst system is required for full virulence in APEC and other bacteria and contributes to resistance of APEC to serum, to cationic antimicrobial peptides and acid shock. The global mechanisms contributing to the attenuation and decreased resistance of the APEC pst mutant to environmental stresses have not been investigated at the transcriptional level. To determine the global effect of a pst mutation on gene expression, we compared the transcriptomes of APEC strain χ7122 and its isogenic pst mutant (K3) grown in phosphate-rich medium.

Results

Overall, 470 genes were differentially expressed by at least 1.5-fold. Interestingly, the pst mutant not only induced systems involved in phosphate acquisition and metabolism, despite phosphate availability, but also modulated stress response mechanisms. Indeed, transcriptional changes in genes associated with the general stress responses, including the oxidative stress response were among the major differences observed. Accordingly, the K3 strain was less resistant to reactive oxygen species (ROS) than the wild-type strain. In addition, the pst mutant demonstrated reduced expression of genes involved in lipopolysaccharide modifications and coding for cell surface components such as type 1 and F9 fimbriae. Phenotypic tests also established that the pst mutant was impaired in its capacity to produce type 1 fimbriae, as demonstrated by western blotting and agglutination of yeast cells, when compared to wild-type APEC strain χ7122.

Conclusion

Overall, our data elucidated the effects of a pst mutation on the transcriptional response, and further support the role of the Pho regulon as part of a complex network contributing to phosphate homeostasis, adaptive stress responses, and E. coli virulence.

The pst operon of enteropathogenic Escherichia coli enhances bacterial adherence to epithelial cells

Enteropathogenic Escherichia coli (EPEC) adheres in vivo and in vitro to epithelial cells. Two main adhesins, the bundle-forming pilus and intimin, encoded by the bfp operon and eae, respectively, are responsible for the localized and the intimate adherence phenotypes. Deletion of the pst operon of EPEC abolishes the transport of inorganic phosphate through the phosphate-specific transport system and causes the constitutive expression of the PHO regulon genes. In the absence of pst there is a decrease in the expression of the main EPEC adhesins and a reduction in bacterial adherence to epithelial cells in vitro. This effect is not related to PHO constitutivity, because a Deltapst phoB double mutant that is defective in the transcription of the PHO genes also displayed low levels of adherence and expression of adhesins. Likewise, a PHO-constitutive phoR mutation did not affect bacterial adherence. The expression of the per operon, which encodes the bfp and ler regulators PerA and PerC, is also negatively affected by the pst deletion. Overall, the data presented here demonstrate that the pst operon of EPEC plays a positive role in the bacterial adherence mechanism by increasing the expression of perA and perC and consequently the transcription of bfp and eae.

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.

Extraintestinal pathogenic Escherichia coli

Extraintestinal pathogenic Escherichia coli (ExPEC) possesses virulence traits that allow it to invade, colonize, and induce disease in bodily sites outside of the gastrointestinal tract. Human diseases caused by ExPEC include urinary tract infections, neonatal meningitis, sepsis, pneumonia, surgical site infections, as well as infections in other extraintestinal locations. ExPEC-induced diseases represent a large burden in terms of medical costs and productivity losses. In addition to human illnesses, ExPEC strains also cause extraintestinal infections in domestic animals and pets. A commonality of virulence factors has been demonstrated between human and animal ExPEC, suggesting that the organisms are zoonotic pathogens. ExPEC strains have been isolated from food products, in particular from raw meats and poultry, indicating that these organisms potentially represent a new class of foodborne pathogens. This review discusses various aspects of ExPEC, including its presence in food products, in animals used for food or as companion pets; the diseases ExPEC can cause; and the virulence factors and virulence mechanisms that cause disease.

Differential effects of epinephrine, norepinephrine, and indole on Escherichia coli O157:H7 chemotaxis, colonization, and gene expression

During infection in the gastrointestinal tract, enterohemorrhagic Escherichia coli (EHEC) O157:H7 is exposed to a wide range of signaling molecules, including the eukaryotic hormones epinephrine and norepinephrine, and bacterial signal molecules such as indole. Since these signaling molecules have been shown to be involved in the regulation of phenotypes such as motility and virulence that are crucial for EHEC infections, we hypothesized that these molecules also govern the initial recognition of the large intestine environment and attachment to the host cell surface. Here, we report that, compared to indole, epinephrine and norepinephrine exert divergent effects on EHEC chemotaxis, motility, biofilm formation, gene expression, and colonization of HeLa cells. Using a novel two-fluorophore chemotaxis assay, it was found that EHEC is attracted to epinephrine and norepinephrine while it is repelled by indole. In addition, epinephrine and norepinephrine also increased EHEC motility and biofilm formation while indole attenuated these phenotypes. DNA microarray analysis of surface-associated EHEC indicated that epinephrine/norepinephrine up-regulated the expression of genes involved in surface colonization and virulence while exposure to indole decreased their expression. The gene expression data also suggested that autoinducer 2 uptake was repressed upon exposure to epinephrine/norepinephrine but not indole. In vitro adherence experiments confirmed that epinephrine and norepinephrine increased attachment to epithelial cells while indole decreased adherence. Taken together, these results suggest that epinephrine and norepinephrine increase EHEC infection while indole attenuates the process.

In vivo gene expression analysis identifies genes required for enhanced colonization of the mouse urinary tract by uropathogenic Escherichia coli strain CFT073 dsdA

Deletional inactivation of the gene encoding d-serine deaminase, dsdA, in uropathogenic Escherichia coli strain CFT073 results in a hypermotile strain with a hypercolonization phenotype in the bladder and kidneys of mice in a model of urinary tract infection (UTI). The in vivo gene expression profiles of CFT073 and CFT073 dsdA were compared by isolating RNA directly from the urine of mice challenged with each strain individually. Hybridization of cDNAs derived from these samples to CFT073-specific microarrays allowed identification of genes that were up- or down-regulated in the dsdA deletion strain during UTI. Up-regulated genes included the known d-serine-responsive gene dsdX, suggesting in vivo intracellular accumulation of d-serine by CFT073 dsdA. Genes encoding F1C fimbriae, both copies of P fimbriae, hemolysin, OmpF, a dipeptide transporter DppA, a heat shock chaperone IbpB, and clusters of open reading frames with unknown functions were also up-regulated. To determine the role of these genes as well as motility in the hypercolonization phenotype, mutants were constructed in the CFT073 dsdA background and tested in competition against the wild type in the murine model of UTI. Strains with deletions of one or both of the two P fimbrial operons, hlyA, fliC, ibpB, c0468, locus c3566 to c3568, or c2485 to c2490 colonized mouse bladders and kidneys at levels indistinguishable from wild type. CFT073 dsdA c2398 and CFT073 dsdA focA maintained a hypercolonization phenotype. A CFT073 dsdA dppA mutant was attenuated 10- to 50-fold in its colonization ability compared to CFT073. Our results support a role for d-serine catabolism and signaling in global virulence gene regulation of uropathogenic E. coli.