Hemolysin of uropathogenic Escherichia coli evokes extensive shedding of the uroepithelium and hemorrhage in bladder tissue within the first 24 hours after intraurethral inoculation of mice

Characterization of Escherichia coli bloodstream isolates associated with mortality

Extra-intestinal pathogenic Escherichia coli (ExPEC) are the predominant cause of Gramnegative bloodstream infections. In this study, 20 E. coli isolates that were the causative agents of bacteraemia and subsequent mortality were characterized. Whole-genome sequencing was used to define the predominant sequence types (ST) among the isolates and to identify virulence factors associated with pathogenicity of ExPEC. The ability of the isolates to resist killing by both serum and polymorphonuclear leukocytes (PMNLs) was also assessed. In line with global trends, ST131 occurred most frequently among the bloodstream isolates and all isolates of this sequence type were multidrug resistant. Other common STs included ST73 and ST69. All isolates encoded multiple virulence factors across a range of categories, including factors involved in adhesion, immune evasion, iron acquisition and synthesis of toxins. None of these factors could be associated with serum and neutrophil resistance. The majority of isolates were resistant to the bactericidal action of serum and PMNLs, and most of those that were sensitive were isolated from patients with compromised immunity.

Molecular Characterization of the Vacuolating Autotransporter Toxin in Uropathogenic Escherichia coli

The vacuolating autotransporter toxin (Vat) contributes to uropathogenic Escherichia coli (UPEC) fitness during systemic infection. Here, we characterized Vat and investigated its regulation in UPEC. We assessed the prevalence of vat in a collection of 45 UPEC urosepsis strains and showed that it was present in 31 (68%) of the isolates. The isolates containing the vat gene corresponded to three major E. coli sequence types (ST12, ST73, and ST95), and these strains secreted the Vat protein. Further analysis of the vat genomic locus identified a conserved gene located directly downstream of vat that encodes a putative MarR-like transcriptional regulator; we termed this gene vatX The vat-vatX genes were present in the UPEC reference strain CFT073, and reverse transcriptase PCR (RT-PCR) revealed that the two genes are cotranscribed. Overexpression of vatX in CFT073 led to a 3-fold increase in vat gene transcription. The vat promoter region contained three putative nucleation sites for the global transcriptional regulator histone-like nucleoid structuring protein (H-NS); thus, the hns gene was mutated in CFT073 (to generate CFT073 hns). Western blot analysis using a Vat-specific antibody revealed a significant increase in Vat expression in CFT073 hns compared to that in wild-type CFT073. Direct H-NS binding to the vat promoter region was demonstrated using purified H-NS in combination with electrophoresis mobility shift assays. Finally, Vat-specific antibodies were detected in plasma samples from urosepsis patients infected by vat-containing UPEC strains, demonstrating that Vat is expressed during infection. Overall, this study has demonstrated that Vat is a highly prevalent and tightly regulated immunogenic serine protease autotransporter protein of Enterobacteriaceae (SPATE) secreted by UPEC during infection.

IMPORTANCE

Uropathogenic Escherichia coli (UPEC) is the major cause of hospital- and community-acquired urinary tract infections. The vacuolating autotransporter toxin (Vat) is a cytotoxin known to contribute to UPEC fitness during murine sepsis infection. In this study, Vat was found to be highly conserved and prevalent among a collection of urosepsis clinical isolates and was expressed at human core body temperature. Regulation of vat was demonstrated to be directly repressed by the global transcriptional regulator H-NS and upregulated by the downstream gene vatX (encoding a new MarR-type transcriptional regulator). Additionally, increased Vat-specific IgG titers were detected in plasma from corresponding urosepsis patients infected with vat-positive isolates. Hence, Vat is a highly conserved and tightly regulated urosepsis-associated virulence factor.

Histone Deacetylase 6 Regulates Bladder Architecture and Host Susceptibility to Uropathogenic Escherichia coli

Histone deacetylase 6 (HDAC6) is a non-canonical, mostly cytosolic histone deacetylase that has a variety of interacting partners and substrates. Previous work using cell-culture based assays coupled with pharmacological inhibitors and gene-silencing approaches indicated that HDAC6 promotes the actin- and microtubule-dependent invasion of host cells by uropathogenic Escherichia coli (UPEC). These facultative intracellular pathogens are the major cause of urinary tract infections. Here, we examined the involvement of HDAC6 in bladder colonization by UPEC using HDAC6 knockout mice. Though UPEC was unable to invade HDAC6(-/-) cells in culture, the bacteria had an enhanced ability to colonize the bladders of mice that lacked HDAC6. This effect was transient, and by six hours post-inoculation bacterial titers in the HDAC6(-/-) mice were reduced to levels seen in wild type control animals. Subsequent analyses revealed that the mutant mice had greater bladder volume capacity and fluid retention, along with much higher levels of acetylated a-tubulin. In addition, infiltrating neutrophils recovered from the HDAC6(-/-) bladder harbored significantly more viable bacteria than their wild type counterparts. Cumulatively, these changes may negate any inhibitory effects that the lack of HDAC6 has on UPEC entry into individual host cells, and suggest roles for HDAC6 in other urological disorders such as urinary retention.

Amplifying renal immunity: the role of antimicrobial peptides in pyelonephritis

Urinary tract infections (UTIs), including pyelonephritis, are among the most common and serious infections encountered in nephrology practice. UTI risk is increased in selected patient populations with renal and urinary tract disorders. As the prevalence of antibiotic-resistant uropathogens increases, novel and alternative treatment options will be needed to reduce UTI-associated morbidity. Discoveries over the past decade demonstrate a fundamental role for the innate immune system in protecting the urothelium from bacterial challenge. Antimicrobial peptides, an integral component of this urothelial innate immune system, demonstrate potent bactericidal activity toward uropathogens and might represent a novel class of UTI therapeutics. The urothelium of the bladder and the renal epithelium secrete antimicrobial peptides into the urinary stream. In the kidney, intercalated cells--a cell-type involved in acid-base homeostasis--have been shown to be an important source of antimicrobial peptides. Intercalated cells have therefore become the focus of new investigations to explore their function during pyelonephritis and their role in maintaining urinary tract sterility. This Review provides an overview of UTI pathogenesis in the upper and lower urinary tract. We describe the role of intercalated cells and the innate immune response in preventing UTI, specifically highlighting the role of antimicrobial peptides in maintaining urinary tract sterility.

Extra-intestinal pathogenic Escherichia coli (ExPEC): Disease, carriage and clones

Extra-intestinal pathogenic Escherichia coli (ExPEC) have a complex phylogeny, broad virulence factor (VF) armament and significant genomic plasticity, and are associated with a spectrum of host infective syndromes ranging from simple urinary tract infection to life-threatening bacteraemia. Their importance as pathogens has come to the fore in recent years, particularly in the context of the global emergence of hyper-virulent and antibiotic resistant strains. Despite this, the mechanisms underlying ExPEC transmission dynamics and clonal selection remain poorly understood. Large-scale epidemiological and clinical studies are urgently required to ascertain the mechanisms underlying these processes to enable the development of novel evidence-based preventative and therapeutic strategies. In the current review, we provide a concise summary of the methods utilised for ExPEC phylogenetic delineation before exploring in detail the associations between ExPEC VFs and site-specific disease. We then consider the role of ExPEC as an intestinal colonist and outline known associations between ExPEC clonal variation, specific disease syndromes and antibiotic resistance.

Virulence factors, antibiotic resistance phenotypes and O-serogroups of Escherichia coli strains isolated from community-acquired urinary tract infection patients in Mexico

BACKGROUND/PURPOSE

Uropathogenic Escherichia coli (UPEC) strains isolated from patients with community-acquired urinary tract infections (UTIs) were assessed to determine the prevalence of virulence genes, antibiotic resistance, and the O-serogroup of the strains.

METHODS

Consenting patients with community-acquired UTI were enrolled at Unidad Médica Familiar Number 64 (Instituto Mexicano del Seguro Social, Estado de Mexico, Mexico) and 321 urine samples were collected. Polymerase chain reaction (PCR) was used to assess 24 virulence genes and 14 O-serogroups. The Kirby-Bauer method was used to evaluate the antibiotic susceptibility of the isolated strains to 12 commonly used antibiotics.

RESULTS

A total of 194 strains were identified as E. coli using standard biochemical tests, followed by PCR amplification of 16S ribosomal RNA gene. Only 58.2% of the strains belonged to the assessed 14 O-serogroups. The serogroups O25, O15, O8, and O75 were present in 20.6%, 17%, 6.1%, and 4.6% of strains, respectively. The most frequently occurring virulence genes among UPEC strains included kpsMT (92.2% strains), usp (87.1%), irp2 (79.3%), iha (64.9%), fim (61.3%), set (36%), astA (33.5%), pap (24.7%), and papGII (21.1%). In addition, 97% of the strains were multi-drug resistant (coresistance to 3-11 antibiotics).

CONCLUSION

The isolated UPEC strains predominantly belonged to three serogroups (O25, O15, and O8), harboured numerous virulence genes, and are multiresistant to antibiotics. The findings of this study could be used to orient UTI treatment strategies and in epidemiological studies in Mexico.

Hemolysin of uropathogenic Escherichia coli: A cloak or a dagger?

Hemolysin from uropathogenic Escherichia coli (UPEC) is a hemolytic and cytotoxic protein active against a broad range of species and cell types. Expression of hemolysin correlates with severity of infection, as up to 78% of UPEC isolates from pyelonephritis cases express hemolysin. Despite decades of research on hemolysin activity, the mechanism of intoxication and the function of hemolysin in UPEC infection remain elusive. Early in vitro research established the role of hemolysin as a lytic protein at high doses. It is hypothesized that hemolysin is secreted at sublytic doses in vivo and recent research has focused on understanding the more subtle effects of hemolysin both in vitro and in elegant infection models in vivo, including inoculation by micropuncture of individual kidney nephrons. As the field continues to evolve, comparisons of hemolysin function in isolates from a range of UTI infections will be important for delineating the role of this toxin. This article is part of a Special Issue entitled: Pore-Forming Toxins edited by Mauro Dalla Serra and Franco Gambale.

Asymptomatic Bacteriuria in Noncatheterized Adults

Asymptomatic bacteriuria (ASB) is a common finding and frequently detected in premenopausal nonpregnant women, institutionalized patients, patients with diabetes mellitus, and the ambulatory elderly population. Despite clear recommendations regarding diagnosis and management of ASB in these populations from the Infectious Diseases Society of America (IDSA), there remains an alarming rate of antimicrobial overuse. This article reviews definitions of ASB, epidemiology of ASB, literature surrounding ASB in diabetic patients, risk factors of ASB, microbiologic data regarding bacterial virulence, use of ASB strains for treatment of symptomatic urinary tract infection, and approaches to addressing translational barriers to implementing IDSA recommendations regarding diagnosis and management of ASB.

Structure of a bacterial toxin-activating acyltransferase

Secreted pore-forming toxins of pathogenic Gram-negative bacteria such as Escherichia coli hemolysin (HlyA) insert into host-cell membranes to subvert signal transduction and induce apoptosis and cell lysis. Unusually, these toxins are synthesized in an inactive form that requires posttranslational activation in the bacterial cytosol. We have previously shown that the activation mechanism is an acylation event directed by a specialized acyl-transferase that uses acyl carrier protein (ACP) to covalently link fatty acids, via an amide bond, to specific internal lysine residues of the protoxin. We now reveal the 2.15-Å resolution X-ray structure of the 172-aa ApxC, a toxin-activating acyl-transferase (TAAT) from pathogenic Actinobacillus pleuropneumoniae. This determination shows that bacterial TAATs are a structurally homologous family that, despite indiscernible sequence similarity, form a distinct branch of the Gcn5-like N-acetyl transferase (GNAT) superfamily of enzymes that typically use acyl-CoA to modify diverse bacterial, archaeal, and eukaryotic substrates. A combination of structural analysis, small angle X-ray scattering, mutagenesis, and cross-linking defined the solution state of TAATs, with intermonomer interactions mediated by an N-terminal α-helix. Superposition of ApxC with substrate-bound GNATs, and assay of toxin activation and binding of acyl-ACP and protoxin peptide substrates by mutated ApxC variants, indicates the enzyme active site to be a deep surface groove.

Role of Hypoxia Inducible Factor-1α (HIF-1α) in Innate Defense against Uropathogenic Escherichia coli Infection

Uropathogenic E. coli (UPEC) is the primary cause of urinary tract infections (UTI) affecting approximately 150 million people worldwide. Here, we revealed the importance of transcriptional regulator hypoxia-inducible factor-1 α subunit (HIF-1α) in innate defense against UPEC-mediated UTI. The effects of AKB-4924, a HIF-1α stabilizing agent, were studied using human uroepithelial cells (5637) and a murine UTI model. UPEC adherence and invasion were significantly reduced in 5637 cells when HIF-1α protein was allowed to accumulate. Uroepithelial cells treated with AKB-4924 also experienced reduced cell death and exfoliation upon UPEC challenge. In vivo, fewer UPEC were recovered from the urine, bladders and kidneys of mice treated transurethrally with AKB-4924, whereas increased bacteria were recovered from bladders of mice with a HIF-1α deletion. Bladders and kidneys of AKB-4924 treated mice developed less inflammation as evidenced by decreased pro-inflammatory cytokine release and neutrophil activity. AKB-4924 impairs infection in uroepithelial cells and bladders, and could be correlated with enhanced production of nitric oxide and antimicrobial peptides cathelicidin and β-defensin-2. We conclude that HIF-1α transcriptional regulation plays a key role in defense of the urinary tract against UPEC infection, and that pharmacological HIF-1α boosting could be explored further as an adjunctive therapy strategy for serious or recurrent UTI.

Urinary tract infection (UTI), commonly caused by uropathogenic E.coli (UPEC), affects more than 150 million people worldwide, resulting in 14 million hospital visits per year and an estimated total cost of 6 billion dollars in direct health care. Due to the high prevalence of UTI and rapid emergence of antibiotic-resistant bacteria, new effective strategies to prevent and treat UTI are urgently needed. Here, we describe a global regulatory role of transcription factor hypoxia-inducible factor-1 (HIF-1) in innate antimicrobial defense against UPEC. HIF-1 stabilization reduces UPEC attachment to and invasion of uroepithelial cells, and protects bladders from UPEC-mediated cytotoxicity in vivo. In the murine UTI model, we found normal bladder HIF-1 expression is required for efficient UPEC clearance, since HIF-1-deficient mice suffer more severe infection than normal mice. Further studies showed that key elements of host protection provided by HIF-1 regulation are uroepithelial cell nitric oxide and antimicrobial peptide production. This study provides valuable insight into the importance of HIF-1 in supporting host immunity during UTI and its potential as a therapeutic target.

Escherichia coli α-hemolysin counteracts the anti-virulence innate immune response triggered by the Rho GTPase activating toxin CNF1 during bacteremia

The detection of the activities of pathogen-encoded virulence factors by the innate immune system has emerged as a new paradigm of pathogen recognition. Much remains to be determined with regard to the molecular and cellular components contributing to this defense mechanism in mammals and importance during infection. Here, we reveal the central role of the IL-1β signaling axis and Gr1+ cells in controlling the Escherichia coli burden in the blood in response to the sensing of the Rho GTPase-activating toxin CNF1. Consistently, this innate immune response is abrogated in caspase-1/11-impaired mice or following the treatment of infected mice with an IL-1β antagonist. In vitro experiments further revealed the synergistic effects of CNF1 and LPS in promoting the maturation/secretion of IL-1β and establishing the roles of Rac, ASC and caspase-1 in this pathway. Furthermore, we found that the α-hemolysin toxin inhibits IL-1β secretion without affecting the recruitment of Gr1+ cells. Here, we report the first example of anti-virulence-triggered immunity counteracted by a pore-forming toxin during bacteremia.

The pathogenic potentials of most microbes depend on a repertoire of virulence factors. Despite major progress in the understanding of the molecular mechanisms underlying the activities of bacterial effectors, little is known about how they cooperate during infection to overcome host immune defenses and promote microbial persistence. Here, we investigated the roles of two uropathogenic Escherichia coli (UPEC) effectors that are co-ordinately expressed, α-hemolysin (HlyA) and cytotoxic necrotizing factor 1 (CNF1). We demonstrated that the HlyA toxin is critical for bacterial stability in the blood and showed that one important role of HlyA is to inhibit the CNF1-induced host response. Collectively, these findings reveal why the coordinated activities of HlyA and CNF1 are necessary for the full virulence of UPEC. Moreover, they unravel a HlyA-driven counter-defense mechanism used by bacteria to facilitate their survival.

Antibodies against hemolysin and cytotoxic necrotizing factor type 1 (CNF1) reduce bladder inflammation in a mouse model of urinary tract infection with toxigenic uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) is the leading cause of cystitis. Cytotoxic necrotizing factor 1 (CNF1) and hemolysin (Hly) are toxins made by approximately 50% of UPEC isolates. CNF1 and Hly contribute to the robust inflammatory response in the bladders of mice challenged with UPEC strain CP9. We hypothesized that antibodies against CNF1 and/or Hly would reduce cystitis caused by CP9. To test this theory, we immunized female C3H/HeOuJ mice subcutaneously with a genetically derived Hly toxoid or genetically derived CNF1 toxoid plus sublethal doses of CNF1. We collected serum and observed increasing titers of specific and neutralizing antibodies against Hly or CNF1 over time. We challenged the mice intraurethrally with CP9 and euthanized them 24 h later. We observed 10-fold lower bacterial titers in the urine of Hly-immunized mice than in that of sham-immunized mice but no difference in kidney bacterial titers. Immunized mice also exhibited significantly less cystitis than sham-immunized mice. In CNF1-vaccinated mice, we detected neither a difference in urine or kidney bacterial titers nor a reduction in the severity of cystitis versus that of sham-immunized mice. We then passively administered an anti-CNF1 monoclonal antibody intraperitoneally to female C3H/HeOuJ mice prior to intraurethral challenge with CP9. Upon challenge, we noted no difference in colonization of the urine or kidney; however, cystitis was reduced significantly in mice treated with the anti-CNF1 antibody versus that in the bladders of mice given an isotype control antibody. Taken together, our data demonstrate that antibodies against CNF1 or Hly reduce the bladder pathology caused by UPEC.

Dysregulation of Escherichia coli α-hemolysin expression alters the course of acute and persistent urinary tract infection

Urinary tract infections (UTIs) are among the most common bacterial infections, causing considerable morbidity in females. Infection is highly recurrent despite appropriate antibiotic treatment. Uropathogenic Escherichia coli (UPEC), the most common causative agent of UTIs, invades bladder epithelial cells (BECs) and develops into clonal intracellular bacterial communities (IBCs). Upon maturation, IBCs disperse, with bacteria spreading to neighboring BECs to repeat this cycle. This process allows UPEC to gain a foothold in the face of innate defense mechanisms, including micturition, epithelial exfoliation, and the influx of polymorphonuclear leukocytes. Here, we investigated the mechanism and dynamics of urothelial exfoliation in the early acute stages of infection. We show that UPEC α-hemolysin (HlyA) induces Caspase-1/Caspase-4-dependent inflammatory cell death in human urothelial cells, and we demonstrate that the response regulator (CpxR)-sensor kinase (CpxA) two-component system (CpxRA), which regulates virulence gene expression in response to environmental signals, is critical for fine-tuning HlyA cytotoxicity. Deletion of the cpxR transcriptional response regulator derepresses hlyA expression, leading to enhanced Caspase-1/Caspase-4- and NOD-like receptor family, pyrin domain containing 3-dependent inflammatory cell death in human urothelial cells. In vivo, overexpression of HlyA during acute bladder infection induces more rapid and extensive exfoliation and reduced bladder bacterial burdens. Bladder fitness is restored fully by inhibition of Caspase-1 and Caspase-11, the murine homolog of Caspase-4. Thus, we have discovered that fine-tuning of HlyA expression by the CpxRA system is critical for enhancing UPEC fitness in the urinary bladder. These results have significant implications for our understanding of how UPEC establishes persistent colonization.

Virulence factors of uropathogenic E. coli and their interaction with the host

Urinary tract infections (UTIs) belong to the most common infectious diseases worldwide. The most frequently isolated pathogen from uncomplicated UTIs is Escherichia coli. To establish infection in the urinary tract, E. coli has to overcome several defence strategies of the host, including the urine flow, exfoliation of urothelial cells, endogenous antimicrobial factors and invading neutrophils. Thus, uropathogenic E. coli (UPEC) harbour a number of virulence and fitness factors enabling the bacterium to resist and overcome these different defence mechanisms. There is no particular factor which allows the identification of UPEC among the commensal faecal flora apart from the ability to enter the urinary tract and cause an infection. Many of potential virulence or fitness factors occur moreover with high redundancy. Fimbriae are inevitable for adherence to and invasion into the host cells; the type 1 pilus is an established virulence factor in UPEC and indispensable for successful infection of the urinary tract. Flagella and toxins promote bacterial dissemination, while different iron-acquisition systems allow bacterial survival in the iron-limited environment of the urinary tract. The immune response to UPEC is primarily mediated by toll-like receptors recognising lipopolysaccharide, flagella and other structures on the bacterial surface. UPEC have the capacity to subvert this immune response of the host by means of actively impacting on pro-inflammatory signalling pathways, or by physical masking of immunogenic structures. The large repertoire of bacterial virulence and fitness factors in combination with host-related differences results in a complex interaction between host and pathogen in the urinary tract.

A conserved PapB family member, TosR, regulates expression of the uropathogenic Escherichia coli RTX nonfimbrial adhesin TosA while conserved LuxR family members TosE and TosF suppress motility

A heterogeneous subset of extraintestinal pathogenic Escherichia coli (ExPEC) strains, referred to as uropathogenic E. coli (UPEC), causes most uncomplicated urinary tract infections. However, no core set of virulence factors exists among UPEC strains. Instead, the focus of the analysis of urovirulence has shifted to studying broad classes of virulence factors and the interactions between them. For example, the RTX nonfimbrial adhesin TosA mediates adherence to host cells derived from the upper urinary tract. The associated tos operon is well expressed in vivo but poorly expressed in vitro and encodes TosCBD, a predicted type 1 secretion system. TosR and TosEF are PapB and LuxR family transcription factors, respectively; however, no role has been assigned to these potential regulators. Thus, the focus of this study was to determine how TosR and TosEF regulate tosA and affect the reciprocal expression of adhesins and flagella. Among a collection of sequenced UPEC strains, 32% (101/317) were found to encode TosA, and nearly all strains (91% [92/101]) simultaneously carried the putative regulatory genes. Deletion of tosR alleviates tosA repression. The tos promoter was localized upstream of tosR using transcriptional fusions of putative promoter regions with lacZ. TosR binds to this region, affecting a gel shift. A 100-bp fragment 220 to 319 bp upstream of tosR inhibits binding, suggesting localization of the TosR binding site. TosEF, on the other hand, downmodulate motility when overexpressed by preventing the expression of fliC, encoding flagellin. Deletion of tosEF increased motility. Thus, we present an additional example of the reciprocal control of adherence and motility.

Chinese herb-resistance and adherence to human uroepithelial cells of uropathogenic Escherichia coli

BACKGROUND

In order to define the virulence factors between Chinese herb-resistant uropathogenic E. coli and susceptible strains, the UPEC isolates were classified into two groups according to its resistance to Chinese herbs.

MATERIALS AND METHODS

The susceptibility profile of strains was determined by disk diffusion method. PCR systems were used to detect genes encoding papC, Aer, hly and cnf1. Isolated human urothelial cells were incubated in vitro and investigated with light microscope immunohistochemistry. Adhesion of E. coli to urothelial cells was studied in vitro.

RESULTS

The results showed that, among the 105 UPEC isolates, 18 were resistant to the herbal concoction. Cnf1 and papC occurred in ≥66.7%, of herb-resistant isolates, while, hly and Aer occurred in 22.2% and 27.8% of strains respectively. Only one gene (Cnf1) occurred in >40%, of Herb-susceptible isolates. Other genes were also found in susceptible isolates: papC (20.7%), hly (11.5%), and Aer (6.9%). Light microscopy and immunochemical investigations demonstrated the normal pelvic transitional epithelial cells cultured. The adherence of strains in both groups increased in 30 min., and reached its peak at 60, (Susceptible E. coli) or 120 min., (Resistant E. coli). The adhesion of the susceptible bacteria to human uroepithelial cells was significantly lower compared with that of the resistant E. coli (p<0.05).

CONCLUSION

These findings revealed that, Chinese herb-resistant uropathogenic E. coli isolates that are hemolytic, and have Aer, papC, hly, Cnf1 genes are more able to be uropathogenic and adherent.

Molecular characterisation of Escherichia coli isolated from hospitalised children and adults with urinary tract infection

Urinary tract infection (UTI) is common amongst children and recurs in 10-30 % of cases. The differences between Escherichia coli strains causing UTI among hospitalised children and adults remains to be fully elucidated. Here, we examined the genetic relatedness and virulence gene (VG) profiles of a collection of E. coli causing UTI among hospitalised children and adults. Genetic relatedness among the strains was investigated using random amplified polymorphic DNA (RAPD) analysis and the strains were characterised using a combination of phylogenetic grouping, the ability to form biofilm and the presence of antigen 43 (Ag43) and its five known alleles, as well 20 VGs associated with uropathogenic E. coli (UPEC). RAPD analysis resolved six major clusters, with two clusters (A and B) consisting almost exclusively of E. coli isolated from children. Isolates from children had a higher prevalence of alpha-haemolysin (hlyA, p < 0.05) and group II capsular polysaccharide synthesis genes (kpsMT II, p < 0.01) than adults. In contrast, E. coli strains from adults had a higher prevalence of invasive ibeA (p < 0.05) and Ag43 (agn43) (p < 0.05) genes, and produced significantly (p < 0.001) more biofilm than E. coli from children. Adult isolates also carried significantly (p < 0.05) more agn43 allele RS218 compared to isolates from children, which carried significantly (p < 0.05) more of the agn43 allele bCFT073. Our results suggest that bacterial virulence factors play an important role in UTI among hospitalised children; however, further research will determine whether these findings apply to a larger cohort and other clinical settings for UTI in children and adults.

Enterococcus faecalis subverts and invades the host urothelium in patients with chronic urinary tract infection

Bacterial urinary tract infections (UTI) are a major growing concern worldwide. Uropathogenic Escherichia coli has been shown to invade the urothelium during acute UTI in mice and humans, forming intracellular reservoirs that can evade antibiotics and the immune response, allowing recurrence at a later date. Other bacterial species, such as Staphylococcus saprophyticus, Klebsiella pneumonia and Salmonella enterica have also been shown to be invasive in acute UTI. However, the role of intracellular infection in chronic UTI causing more subtle lower urinary tract symptoms (LUTS), a particular problem in the elderly population, is poorly understood. Moreover, the species of bacteria involved remains largely unknown. A previous study of a large cohort of non-acute LUTS patients found that Enterococcus faecalis was frequently found in urine specimens. E. faecalis accounts for a significant proportion of chronic bladder infections worldwide, although the invasive lifestyle of this uropathogen has yet to be reported. Here, we wanted to explore this question in more detail. We harvested urothelial cells shed in response to inflammation and, using advanced imaging techniques, inspected them for signs of bacterial pathology and invasion. We found strong evidence of intracellular E. faecalis harboured within urothelial cells shed from the bladder of LUTS patients. Furthermore, using a culture model system, these patient-isolated strains of E. faecalis were able to invade a transitional carcinoma cell line. In contrast, we found no evidence of cellular invasion by E. coli in the patient cells or the culture model system. Our data show that E. faecalis is highly competent to invade in this context; therefore, these results have implications for both the diagnosis and treatment of chronic LUTS.

Structural and functional integrity of spermatozoa is compromised as a consequence of acute uropathogenic E. coli-associated epididymitis

Uropathogenic Escherichia coli (UPEC)-associated epididymitis is commonly diagnosed in outpatient settings. Although the infection can be successfully cleared using antimicrobial medications, 40% of patients unexplainably show persistent impaired semen parameters even after treatment. Our aim was to investigate whether pathogenic UPEC and its associated virulence factor hemolysin (hlyA) perturb the structural and functional integrity of both the epididymis and sperm, actions that may be responsible for the observed impairment and possibly a reduction of fertilization capabilities. Semen collected from patients diagnosed with E. coli-only related epididymitis showed that sperm counts were low 14 days postantimicrobial treatment regardless of hlyA status. At Day 84 following treatment, hlyA production correlated with approximately 4-fold lower sperm concentrations than in men with hlyA-negative strains. In vivo experiments with the hlyA-producing UPEC CFT073 strain in a murine epididymitis model showed that just 3 days postinfection, structural damage to the epididymis (epithelial damage, leukocyte infiltration, and edema formation) was present. This was more severe in UPEC CFT073 compared to nonpathogenic E. coli (NPEC 470) infection. Moreover, pathogenic UPEC strains prematurely activated the acrosome in vivo and in vitro. Raman microspectroscopy revealed that UPEC CFT073 undermined sperm integrity by inducing nuclear DNA damage. Consistent with these observations, the in vitro fertilization capability of hlyA-treated mouse sperm was completely abolished, although sperm were motile. These findings provide new insights into understanding the possible processes underlying clinical manifestations of acute epididymitis.

Protective effect of mitochondria-targeted antioxidants in an acute bacterial infection

Acute pyelonephritis is a potentially life-threatening infection of the upper urinary tract. Inflammatory response and the accompanying oxidative stress can contribute to kidney tissue damage, resulting in infection-induced intoxication that can become fatal in the absence of antibiotic therapy. Here, we show that pyelonephritis was associated with oxidative stress and renal cell death. Oxidative stress observed in pyelonephritic kidney was accompanied by a reduced level of mitochondrial B-cell lymphoma 2 (Bcl-2). Importantly, renal cell death and animal mortality were both alleviated by mitochondria-targeted antioxidant 10(6'-plastoquinonyl) decylrhodamine 19 (SkQR1). These findings suggest that pyelonephritis can be treated by reducing mitochondrial reactive oxygen species and thus by protecting mitochondrial integrity and lowering kidney damage.

Genetic analysis of the role of yfiR in the ability of Escherichia coli CFT073 to control cellular cyclic dimeric GMP levels and to persist in the urinary tract

During urinary tract infections (UTIs), uropathogenic Escherichia coli must maintain a delicate balance between sessility and motility to achieve successful infection of both the bladder and kidneys. Previous studies showed that cyclic dimeric GMP (c-di-GMP) levels aid in the control of the transition between motile and nonmotile states in E. coli. The yfiRNB locus in E. coli CFT073 contains genes for YfiN, a diguanylate cyclase, and its activity regulators, YfiR and YfiB. Deletion of yfiR yielded a mutant that was attenuated in both the bladder and the kidneys when tested in competition with the wild-type strain in the murine model of UTI. A double yfiRN mutant was not attenuated in the mouse model, suggesting that unregulated YfiN activity and likely increased cytoplasmic c-di-GMP levels cause a survival defect. Curli fimbriae and cellulose production were increased in the yfiR mutant. Expression of yhjH, a gene encoding a proven phosphodiesterase, in CFT073 ΔyfiR suppressed the overproduction of curli fimbriae and cellulose and further verified that deletion of yfiR results in c-di-GMP accumulation. Additional deletion of csgD and bcsA, genes necessary for curli fimbriae and cellulose production, respectively, returned colonization levels of the yfiR deletion mutant to wild-type levels. Peroxide sensitivity assays and iron acquisition assays displayed no significant differences between the yfiR mutant and the wild-type strain. These results indicate that dysregulation of c-di-GMP production results in pleiotropic effects that disable E. coli in the urinary tract and implicate the c-di-GMP regulatory system as an important factor in the persistence of uropathogenic E. coli in vivo.

The RTX pore-forming toxin α-hemolysin of uropathogenic Escherichia coli: progress and perspectives

Members of the RTX family of protein toxins are functionally conserved among an assortment of bacterial pathogens. By disrupting host cell integrity through their pore-forming and cytolytic activities, this class of toxins allows pathogens to effectively tamper with normal host cell processes, promoting pathogenesis. Here, we focus on the biology of RTX toxins by describing salient properties of a prototype member, α-hemolysin, which is often encoded by strains of uropathogenic Escherichia coli. It has long been appreciated that RTX toxins can have distinct effects on host cells aside from outright lysis. Recently, advances in modeling and analysis of host-pathogen interactions have led to novel findings concerning the consequences of pore formation during host-pathogen interactions. We discuss current progress on longstanding questions concerning cell specificity and pore formation, new areas of investigation that involve toxin-mediated perturbations of host cell signaling cascades and perspectives on the future of RTX toxin investigation.

Role of pore-forming toxins in bacterial infectious diseases

Pore-forming toxins (PFTs) are the most common bacterial cytotoxic proteins and are required for virulence in a large number of important pathogens, including Streptococcus pneumoniae, group A and B streptococci, Staphylococcus aureus, Escherichia coli, and Mycobacterium tuberculosis. PFTs generally disrupt host cell membranes, but they can have additional effects independent of pore formation. Substantial effort has been devoted to understanding the molecular mechanisms underlying the functions of certain model PFTs. Likewise, specific host pathways mediating survival and immune responses in the face of toxin-mediated cellular damage have been delineated. However, less is known about the overall functions of PFTs during infection in vivo. This review focuses on common themes in the area of PFT biology, with an emphasis on studies addressing the roles of PFTs in in vivo and ex vivo models of colonization or infection. Common functions of PFTs include disruption of epithelial barrier function and evasion of host immune responses, which contribute to bacterial growth and spreading. The widespread nature of PFTs make this group of toxins an attractive target for the development of new virulence-targeted therapies that may have broad activity against human pathogens.

Role of pore-forming toxins in neonatal sepsis

Protein toxins are important virulence factors contributing to neonatal sepsis. The major pathogens of neonatal sepsis, group B Streptococci, Escherichia coli, Listeria monocytogenes, and Staphylococcus aureus, secrete toxins of different molecular nature, which are key for defining the disease. Amongst these toxins are pore-forming exotoxins that are expressed as soluble monomers prior to engagement of the target cell membrane with subsequent formation of an aqueous membrane pore. Membrane pore formation is not only a means for immediate lysis of the targeted cell but also a general mechanism that contributes to penetration of epithelial barriers and evasion of the immune system, thus creating survival niches for the pathogens. Pore-forming toxins, however, can also contribute to the induction of inflammation and hence to the manifestation of sepsis. Clearly, pore-forming toxins are not the sole factors that drive sepsis progression, but they often act in concert with other bacterial effectors, especially in the initial stages of neonatal sepsis manifestation.

Cytotoxic necrotizing factor 1 and hemolysin from uropathogenic Escherichia coli elicit different host responses in the murine bladder

Cytotoxic necrotizing factor 1 (CNF1) and hemolysin (HlyA1) are toxins produced by uropathogenic Escherichia coli (UPEC). We previously showed that these toxins contribute to the inflammation and tissue damage seen in a mouse model of ascending urinary tract infection. CNF1 constitutively activates small Rho GTPases by deamidation of a conserved glutamine residue, and HlyA1 forms pores in eukaryotic cell membranes. In this study, we used cDNA microarrays of bladder tissue isolated from mice infected intraurethrally with wild-type CP9, CP9cnf1, or CP9ΔhlyA to further evaluate the role that each toxin plays in the host response to UPEC. Regardless of the strain used, we found that UPEC itself elicited a significant change in host gene expression 24 h after inoculation. The largest numbers of upregulated genes were in the cytokine and chemokine signaling and Toll-like receptor signaling pathways. CNF1 exerted a strong positive influence on expression of genes involved in innate immunity and signal transduction and a negative impact on metabolism- and transport-associated genes. HlyA1 evoked an increase in expression of genes that encode innate immunity factors and a decrease in expression of genes involved in cytoskeletal and metabolic processes. Multiplex cytokine and myeloperoxidase assays corroborated our finding that a strong proinflammatory response was elicited by all strains tested. Bladders challenged intraurethrally with purified CNF1 displayed pathology similar to but significantly less intense than the pathology that we observed in CP9-challenged mice. Our data demonstrate substantial roles for CNF1 and HlyA1 in initiation of a strong proinflammatory response to UPEC in the bladder.

Virulence profile of different phylogenetic groups of locally isolated community acquired uropathogenic E. coli from Faisalabad region of Pakistan

Background

Uropathogenic E.coli (UPEC) are among major pathogens causing urinary tract infections. Virulence factors are mainly responsible for the severity of these emerging infections. This study was planned to investigate the distribution of virulence genes and cytotoxic effects of UPEC isolates with reference to phylogenetic groups (B2, B1, D and A) to understand the presence and impact of virulence factors in the severity of infection in Faisalabad region of Pakistan.

Methods

In this study phylogenetic analysis, virulence gene identification and cytotoxicity of 59 uropathogenic E.coli isolates obtained from non-hospitalized patients was studied.

Results

Among 59 isolates, phylogenetic group B2 (50%) was most dominant followed by groups A, B1 (19% each) and D (12%). Isolates present in group D showed highest presence of virulence genes. The prevalence hlyA (37%) was highest followed by sfaDE (27%), papC (24%), cnf1 (20%), eaeA (19%) and afaBC3 (14%). Highly hemolytic and highly verotoxic isolates mainly belonged to group D and B2. We also found two isolates with simultaneous presence of three fimbrial adhesin genes present on pap, afa, and sfa operons. This has not been reported before and underlines the dynamic nature of these UPEC isolates.

Conclusions

It was concluded that in local UPEC isolates from non-hospitalized patients, group B2 was more prevalent. However, group D isolates were most versatile as all were equipped with virulence genes and showed highest level of cytotoxicity.

Preventing urinary tract infection: progress toward an effective Escherichia coli vaccine

Uncomplicated urinary tract infections (UTIs) are common, with nearly half of all women experiencing at least one UTI in their lifetime. This high frequency of infection results in huge annual economic costs, decreased workforce productivity and high patient morbidity. At least 80% of these infections are caused by uropathogenic Escherichia coli (UPEC). UPEC can reside side by side with commensal strains in the gastrointestinal tract and gain access to the bladder via colonization of the urethra. Antibiotics represent the current standard treatment for UTI; however, even after treatment, patients frequently suffer from recurrent infection with the same or different strains. In addition, successful long-term treatment has been complicated by a rise in both the number of antibiotic-resistant strains and the prevalence of antibiotic-resistance mechanisms. As a result, preventative approaches to UTI, such as vaccination, have been sought. This review summarizes recent advances in UPEC vaccine development and outlines future directions for the field.

The UPEC pore-forming toxin α-hemolysin triggers proteolysis of host proteins to disrupt cell adhesion, inflammatory, and survival pathways

Uropathogenic Escherichia coli (UPEC), which are the leading cause of both acute and chronic urinary tract infections, often secrete a labile pore-forming toxin known as α-hemolysin (HlyA). We show that stable insertion of HlyA into epithelial cell and macrophage membranes triggers degradation of the cytoskeletal scaffolding protein paxillin and other host regulatory proteins, as well as components of the proinflammatory NFκB signaling cascade. Proteolysis of these factors requires host serine proteases, and paxillin degradation specifically involves the serine protease mesotrypsin. The induced activation of mesotrypsin by HlyA is preceded by redistribution of mesotrypsin precursors from the cytosol into foci along microtubules and within nuclei. HlyA intoxication also stimulated caspase activation, which occurred independently of effects on host serine proteases. HlyA-induced proteolysis of host proteins likely allows UPEC to not only modulate epithelial cell functions, but also disable macrophages and suppress inflammatory responses.

The repeat-in-toxin family member TosA mediates adherence of uropathogenic Escherichia coli and survival during bacteremia

Uropathogenic Escherichia coli (UPEC) is responsible for the majority of uncomplicated urinary tract infections (UTI) and represents the most common bacterial infection in adults. UPEC utilizes a wide range of virulence factors to colonize the host, including the novel repeat-in-toxin (RTX) protein TosA, which is specifically expressed in the host urinary tract and contributes significantly to the virulence and survival of UPEC. tosA, found in strains within the B2 phylogenetic subgroup of E. coli, serves as a marker for strains that also contain a large number of well-characterized UPEC virulence factors. The presence of tosA in an E. coli isolate predicts successful colonization of the murine model of ascending UTI, regardless of the source of the isolate. Here, a detailed analysis of the function of tosA revealed that this gene is transcriptionally linked to genes encoding a conserved type 1 secretion system similar to other RTX family members. TosA localized to the cell surface and was found to mediate (i) adherence to host cells derived from the upper urinary tract and (ii) survival in disseminated infections and (iii) to enhance lethality during sepsis (as assessed in two different animal models of infection). An experimental vaccine, using purified TosA, protected vaccinated animals against urosepsis. From this work, it was concluded that TosA belongs to a novel group of RTX proteins that mediate adherence and host damage during UTI and urosepsis and could be a novel target for the development of therapeutics to treat ascending UTIs.

Do Escherichia coli strains causing acute cystitis have a distinct virulence repertoire?

Bacterial virulence factors influence the site and severity of urinary tract infections. While pyelonephritis-associated molecular traits have been defined, virulence factors specific for acute cystitis strains have not been identified. This study examined the virulence factor repertoire of 247 Escherichia coli strains, prospectively isolated from women with community-acquired acute cystitis. Fim sequences were present in 96% of the isolates, which also expressed Type 1 fimbriae. Curli were detected in 75%, 13% of which formed cellulose. Pap sequences were present in 47%, 27% were papG+, 23% were prsG+ and 42% expressed P fimbriae. TcpC was expressed by 33% of the strains, 32% in a subgroup of patients who only had symptoms of cystitis and 42% in patients with signs of upper urinary tract involvement; most frequently by the papG+/prsG+ subgroup. Strains with the full fim, pap and TcpC and curli virulence profile were more common in cystitis patients with than in patients without upper tract involvement (p < 0.05). The varied virulence profile of E. coli strains causing acute cystitis suggests that diverse bacterial strains, expressing Type 1 fimbriae trigger a convergent host response, involving pathways that give rise to the characteristic symptoms of acute cystitis.

Presence of putative repeat-in-toxin gene tosA in Escherichia coli predicts successful colonization of the urinary tract

Uropathogenic Escherichia coli (UPEC) strains, which cause the majority of uncomplicated urinary tract infections (UTIs), carry a unique assortment of virulence or fitness genes. However, no single defining set of virulence or fitness genes has been found in all strains of UPEC, making the differentiation between UPEC and fecal commensal strains of E. coli difficult without the use of animal models of infection or phylogenetic grouping. In the present study, we consider three broad categories of virulence factors simultaneously to better define a combination of virulence factors that predicts success in the urinary tract. A total of 314 strains of E. coli, representing isolates from fecal samples, asymptomatic bacteriuria, complicated UTIs, and uncomplicated bladder and kidney infections, were assessed by multiplex PCR for the presence of 15 virulence or fitness genes encoding adhesins, toxins, and iron acquisition systems. The results confirm previous reports of gene prevalence among isolates from different clinical settings and identify several new patterns of gene associations. One gene, tosA, a putative repeat-in-toxin (RTX) homolog, is present in 11% of fecal strains but 25% of urinary isolates. Whereas tosA-positive strains carry an unusually high number (11.2) of the 15 virulence or fitness genes, tosA-negative strains have an average of only 5.4 virulence or fitness genes. The presence of tosA was predictive of successful colonization of a murine model of infection, even among fecal isolates, and can be used as a marker of pathogenic strains of UPEC within a distinct subset of the B2 lineage.

IMPORTANCE

Escherichia coli is the primary cause of urinary tract infections, the most common bacterial infection of humans. Virulence of a uropathogenic strain is typically defined by the clinical source of the isolate, the ability to colonize the bladder and kidneys in a murine model, the phylogenetic group of the bacterium, and virulence gene content. Here we describe a novel single gene, the repeat-in-toxin gene tosA, the presence of which predicts virulence of E. coli isolates regardless of source. Rapid identification of uropathogenic strains of E. coli may aid in the development of therapeutic and preventive therapies.

Identification of in vivo-induced antigens including an RTX family exoprotein required for uropathogenic Escherichia coli virulence

Uncomplicated urinary tract infections (UTI) are caused most commonly by uropathogenic Escherichia coli (UPEC). Whole-genome screening approaches, including transcriptomic, proteomic, and signature-tagged mutagenesis, have shown that UPEC highly expresses or requires genes for translational machinery, capsule, lipopolysaccharide, type 1 fimbriae, and iron acquisition systems during UTI. To identify additional genes expressed by UPEC during UTI, an immunoscreening approach termed in vivo-induced antigen technology (IVIAT) was employed to identify antigens produced during experimental infection that are not produced during in vitro culture. An inducible protein expression library, constructed from genomic DNA isolated from UPEC strain CFT073, was screened using exhaustively adsorbed pooled sera from 20 chronically infected female CBA/J mice. Using this approach, we identified 93 antigens induced by UPEC in vivo. A representative subset of these genes was tested by quantitative PCR for expression by CFT073 in vivo and during growth in human urine or LB medium in vitro; proWX, narJI, lolA, lolD, tosA (upxA), c2432, katG, ydhX, kpsS, and yddQ were poorly expressed in vitro but highly expressed in vivo. Of these, tosA, a gene encoding a predicted repeat-in-toxin family member, was expressed exclusively during UTI. Deletion of tosA in UPEC strain CFT073 resulted in significant attenuation in bladder and kidney infections during ascending UTI. By screening for in vivo-induced antigens, we identified a novel UPEC virulence factor and additional proteins that could be useful as potential vaccine targets.

Dissemination and systemic colonization of uropathogenic Escherichia coli in a murine model of bacteremia

Infection with uropathogenic Escherichia coli (UPEC), the causative agent of most uncomplicated urinary tract infections, proceeds in an ascending manner and, if left untreated, may result in bacteremia and urosepsis. To examine the fate of UPEC after its entry into the bloodstream, we developed a murine model of sublethal bacteremia. CBA/J mice were inoculated intravenously with 1 × 10⁶ CFU of pyelonephritis strain E. coli CFT073 carrying a bioluminescent reporter. Biophotonic imaging, used to monitor the infection over 48 h, demonstrated that the bacteria disseminated systemically and appeared to localize at discrete sites. UPEC was recovered from the spleen, liver, kidneys, lungs, heart, brain, and intestines as early as 20 min postinoculation, peaking at 24 h postinoculation. A nonpathogenic E. coli K-12 strain, however, disseminated at significantly lower levels (P < 0.01) and was cleared from the liver and cecum by 24 h postinoculation. Isogenic mutants lacking type 1 fimbriae, P fimbriae, capsule, TonB, the heme receptors Hma and ChuA, or particularly the sialic acid catabolism enzyme NanA were significantly outcompeted by wild-type CFT073 during bacteremia (P < 0.05), while flagellin and hemolysin mutants were not.

E.  coli is the primary cause of urinary tract infections. In severe cases of kidney infection, bacteria can enter the bloodstream and cause systemic disease. While the ability of E. coli to cause urinary tract infection has been extensively studied, the fate of these bacteria once they enter the bloodstream is largely unknown. Here we used an imaging technique to develop a mouse model of E. coli bloodstream infection and identify bacterial genes that are important for the bacteria to spread to and infect various organs. Understanding how urinary tract pathogens like E. coli cause disease after they enter the bloodstream may aid in the development of protective and therapeutic treatments.

Escherichia coli global gene expression in urine from women with urinary tract infection

Murine models of urinary tract infection (UTI) have provided substantial data identifying uropathogenic E. coli (UPEC) virulence factors and assessing their expression in vivo. However, it is unclear how gene expression in these animal models compares to UPEC gene expression during UTI in humans. To address this, we used a UPEC strain CFT073-specific microarray to measure global gene expression in eight E. coli isolates monitored directly from the urine of eight women presenting at a clinic with bacteriuria. The resulting gene expression profiles were compared to those of the same E. coli isolates cultured statically to exponential phase in pooled, sterilized human urine ex vivo. Known fitness factors, including iron acquisition and peptide transport systems, were highly expressed during human UTI and support a model in which UPEC replicates rapidly in vivo. While these findings were often consistent with previous data obtained from the murine UTI model, host-specific differences were observed. Most strikingly, expression of type 1 fimbrial genes, which are among the most highly expressed genes during murine experimental UTI and encode an essential virulence factor for this experimental model, was undetectable in six of the eight E. coli strains from women with UTI. Despite the lack of type 1 fimbrial expression in the urine samples, these E. coli isolates were generally capable of expressing type 1 fimbriae in vitro and highly upregulated fimA upon experimental murine infection. The findings presented here provide insight into the metabolic and pathogenic profile of UPEC in urine from women with UTI and represent the first transcriptome analysis for any pathogenic E. coli during a naturally occurring infection in humans.

Animal models of infection have been used extensively to study how bacteria and other pathogens cause disease. These models provide valuable information and have led to the development of numerous vaccines and antimicrobial therapies. However, it is important to recognize how these animal models compare to human infection and to understand how bacteria cause disease in humans. This study measured gene expression in E. coli, a major cause of urinary tract infection, immediately after collection from the urine of women with bladder infection symptoms. The data showed that E. coli gene expression in the urine from women with urinary tract infection was very often similar to what had been observed in a mouse model, but these studies also identified several potentially important differences, including a bacterial surface structure that is necessary for infection in mice but not detected in most E. coli in human urine. Although more precise measurements are still needed, these findings contribute to our understanding of bacterial infection in humans and will help in the development of vaccines and treatments for urinary tract infection.

Host-pathogen interactions in urinary tract infection

The urinary tract is a common site of bacterial infections; nearly half of all women experience at least one urinary tract infection (UTI) during their lifetime. These infections are classified based on the condition of the host. Uncomplicated infections affect otherwise healthy individuals and are most commonly caused by uropathogenic Escherichia coli, whereas complicated infections affect patients with underlying difficulties, such as a urinary tract abnormality or catheterization, and are commonly caused by species such as Proteus mirabilis. Virulence and fitness factors produced by both pathogens include fimbriae, toxins, flagella, iron acquisition systems, and proteins that function in immune evasion. Additional factors that contribute to infection include the formation of intracellular bacterial communities by E. coli and the production of urease by P. mirabilis, which can result in urinary stone formation. Innate immune responses are induced or mediated by pattern recognition receptors, antimicrobial peptides, and neutrophils. The adaptive immune response to UTI is less well understood. Host factors TLR4 and CXCR1 are implicated in disease outcome and susceptibility, respectively. Low levels of TLR4 are associated with asymptomatic bacteriuria while low levels of CXCR1 are associated with increased incidence of acute pyelonephritis. Current research is focused on the identification of additional virulence factors and therapeutic or prophylactic targets that might be used in the generation of vaccines against both uropathogens.

Modulation of ureteric Ca signaling and contractility in humans and rats by uropathogenic E. coli

Ascending urinary tract infections, a significant cause of kidney damage, are predominantly caused by uropathogenic Escherichia coli (UPEC). However, the role and mechanism of changes in ureteric function during infection are poorly understood. We therefore investigated the effects of UPEC on Ca signaling and contractions in rat (n = 17) and human (n = 6) ureters. Ca transients and force were measured and effects of UPEC on the urothelium were monitored in live tissues. In both species, luminal exposure of ureters to UPEC strains J96 and 536 caused significant time-dependent decreases in phasic and high K depolarization-induced contractility, associated with decreases in the amplitude and duration of the Ca transients. These changes were significant after 3-5 h and irreversible over the next 5 h. The infection causes increased activity of K channels, causing inhibition of voltage-gated Ca entry, and K channel blockers could reverse the effects of UPEC on ureteric function. A smaller direct effect on Ca entry also occurs. Nonpathogenic E. coli (TG2) or abluminal application of UPEC did not produce changes in Ca signaling or contractility. UPEC exposure also caused significant impairment of urothelial barrier function; luminal application of the Ca channel blocker nifedipine caused a reduction in contractions as it entered the tissue, an effect not observed in untreated ureters. Thus, UPEC impairs ureteric contractility in a Ca-dependent manner, largely caused by stimulation of potassium channels and this mechanism is dependent on host-urothelium interaction.

Use of zebrafish to probe the divergent virulence potentials and toxin requirements of extraintestinal pathogenic Escherichia coli

Extraintestinal pathogenic E. coli (ExPEC) cause an array of diseases, including sepsis, neonatal meningitis, and urinary tract infections. Many putative virulence factors that might modulate ExPEC pathogenesis have been identified through sequencing efforts, epidemiology, and gene expression profiling, but few of these genes have been assigned clearly defined functional roles during infection. Using zebrafish embryos as surrogate hosts, we have developed a model system with the ability to resolve diverse virulence phenotypes and niche-specific restrictions among closely related ExPEC isolates during either localized or systemic infections. In side-by-side comparisons of prototypic ExPEC isolates, we observed an unexpectedly high degree of phenotypic diversity that is not readily apparent using more traditional animal hosts. In particular, the capacity of different ExPEC isolates to persist and multiply within the zebrafish host and cause disease was shown to be variably dependent upon two secreted toxins, α-hemolysin and cytotoxic necrotizing factor. Both of these toxins appear to function primarily in the neutralization of phagocytes, which are recruited in high numbers to sites of infection where they act as an essential host defense against ExPEC as well as less virulent E. coli strains. These results establish zebrafish as a valuable tool for the elucidation and functional analysis of both ExPEC virulence factors and host defense mechanisms.

Escherichia coli can exist among the normal intestinal microbiota without causing any overt problems for the human host. However, humans as well as other animals can often acquire less-mild mannered variants of E. coli strains known as extraintestinal pathogenic E. coli (ExPEC) that can colonize sites outside of the intestinal tract and cause a range of serious illnesses, including sepsis, meningitis, and urinary tract infections. Despite many advances over the years using cell culture and rodent infection models, the spectrum of genes that control the ability of different ExPEC strains to colonize and grow within specific host niches and cause disease remain, for the most part, elusive. Here, we report the development of a new model system that uses zebrafish as surrogate hosts for ExPEC and related isolates. Using zebrafish to model both localized and systemic infections, we found that closely related ExPEC isolates display an unexpected array of virulence characteristics and toxin requirements that are not readily apparent from genomic information alone. This model system is amenable to high-throughput genetic and pharmacological screens and should prove useful in the development of more efficacious therapeutics.

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.

Histone-like nucleoid-structuring protein represses transcription of the ehx operon carried by locus of enterocyte effacement-negative Shiga toxin-expressing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) are a significant cause of zoonotic foodborne diarrheal disease in industrialized nations. In addition to Shiga toxin most STEC produce the enterohemolysin (EhxA) toxin. The EhxA toxin is encoded by the ehxCABD operon located on the large plasmid carried by STEC, yet its role in pathogenesis is unknown. A histone-like nucleoid-structuring protein (H-NS) null mutant of STEC O91:H21 strain B2F1 displayed a hyper-hemolytic phenotype, was defective in binding to human colonic epithelial cells, and was non-motile. We concluded that H-NS modulated expression of several genes in B2F1 including the ehx operon. Electrophoretic mobility shift assays indicate that H-NS binds to an 88bp region of DNA upstream of the ehxC start codon. To determine if the same region of DNA was sensitive to repression by H-NS, a transcriptional fusion was constructed between the putative promoter region of ehx and a promoterless lacZ gene. The beta-galactosidase activity detected was low in E. coli that produced H-NS but was significantly higher in the H-NS null background. Taken together, the data indicates that in STEC the 88bp region upstream of the ehx operon contains a cis-acting element to which H-NS binds and negatively regulates expression of enterohemolysin.

Urothelial cultures support intracellular bacterial community formation by uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) causes most community-acquired and nosocomial urinary tract infections (UTI). In a mouse model of UTI, UPEC invades superficial bladder cells and proliferates rapidly, forming biofilm-like structures called intracellular bacterial communities (IBCs). Using a gentamicin protection assay and fluorescence microscopy, we developed an in vitro model for studying UPEC proliferation within immortalized human urothelial cells. By pharmacologic manipulation of urothelial cells with the cholesterol-sequestering drug filipin, numbers of intracellular UPEC CFU increased 8 h and 24 h postinfection relative to untreated cultures. Enhanced UPEC intracellular proliferation required that the urothelial cells, but not the bacteria, be filipin treated prior to infection. However, neither UPEC frequency of invasion nor early intracellular trafficking events to a Lamp1-positive compartment were modulated by filipin. Upon inspection by fluorescence microscopy, cultures with enhanced UPEC intracellular proliferation exhibited large, dense bacterial aggregates within cells that resembled IBCs but were contained with Lamp1-positive vacuoles. While an isogenic fimH mutant was capable of forming these IBC-like structures, the mutant formed significantly fewer than wild-type UPEC. Similar to IBCs, expression of E. coli iron acquisition systems was upregulated by intracellular UPEC. Expression of other putative virulence factors, including hlyA, cnf1, fliC, kpsD, and the biofilm adhesin yfaL also increased, while expression of fimA decreased and that of flu did not change. These results indicate that UPEC differentially regulates virulence factors in the intracellular environment. Thus, immortalized urothelial cultures that recapitulate IBC formation in vitro represent a novel system for the molecular and biochemical characterization of the UPEC intracellular life cycle.

Vaccination with proteus toxic agglutinin, a hemolysin-independent cytotoxin in vivo, protects against Proteus mirabilis urinary tract infection

Complicated urinary tract infections (UTI) caused by Proteus mirabilis are associated with severe pathology in the bladder and kidney. To investigate the roles of two established cytotoxins, the HpmA hemolysin, a secreted cytotoxin, and proteus toxic agglutinin (Pta), a surface-associated cytotoxin, mutant analysis was used in conjunction with a mouse model of ascending UTI. Inactivation of pta, but not inactivation of hpmA, resulted in significant decreases in the bacterial loads of the mutant in kidneys (P < 0.01) and spleens (P < 0.05) compared to the bacterial loads of the wild type; the 50% infective dose (ID(50)) of an isogenic pta mutant or hpmA pta double mutant was 100-fold higher (5 x 10(8) CFU) than the ID(50) of parent strain HI4320 (5 x 10(6) CFU). Colonization by the parent strain caused severe cystitis and interstitial nephritis as determined by histopathological examination. Mice infected with the same bacterial load of the hpmA pta double mutant showed significantly reduced pathology (P < 0.01), suggesting that the additive effect of these two cytotoxins is critical during Proteus infection. Since Pta is surface associated and important for the persistence of P. mirabilis in the host, it was selected as a vaccine candidate. Mice intranasally vaccinated with a site-directed (indicated by an asterisk) (S366A) mutant purified intact toxin (Pta*) or the passenger domain Pta-alpha*, each independently conjugated with cholera toxin (CT), had significantly lower bacterial counts in their kidneys ( P = 0.001) and spleens (P = 0.002) than mice that received CT alone. The serum immunoglobulin G levels correlated with protection (P = 0.03). This is the first report describing the in vivo cytotoxicity and antigenicity of an autotransporter in P. mirabilis and its use in vaccine development.

Cytotoxic necrotizing factor type 1-neutralizing monoclonal antibody NG8 recognizes three amino acids in a C-terminal region of the toxin and reduces toxin binding to HEp-2 cells

Cytotoxic necrotizing factor type 1 (CNF1) and CNF2 are toxins of pathogenic Escherichia coli that share 85% identity over 1,014 amino acids. Although both of these toxins modify GTPases, CNF1 is a more potent inducer of multinucleation in HEp-2 cells, binds more efficiently to HEp-2 cells, and, despite the conservation of amino acids (C866 and H881) required for enzymatic activity of the toxins, deamidates RhoA and Cdc42 better than CNF2. Here we exploited the differences between CNF1 and CNF2 to define the epitope on CNF1 to which the CNF1-specific neutralizing monoclonal antibody (MAb) (MAb NG8) binds and to determine the mechanism by which MAb NG8 neutralizes CNF1 activity on HEp-2 cells. For these purposes, we generated a panel of 21 site-directed mutants in which amino acids in CNF1 were exchanged for the amino acids in CNF2 between amino acids 546 and 869 and vice versa. This region of CNF1 not only is recognized by MAb NG8 but also is involved in binding of this toxin to HEp-2 cells. All the mutants retained the capacity to induce multinucleation of HEp-2 cells. However, the CNF1 double mutant with D591E and F593L mutations (CNF1(D591E F593L)) and the CNF1(H661Q) single mutant displayed drastically reduced reactivity with MAb NG8. A reverse chimeric triple mutant, CNF1(E591D L593F Q661H), imparted MAb NG8 reactivity to CNF2. MAb NG8 neutralized CNF2(E591D L593F Q661H) activity in a dose-dependent manner and reduced the binding of this chimeric toxin to HEp-2 cells. Taken together, these results pinpoint three amino acids in CNF1 that are key amino acids for recognition by neutralizing MAb NG8 and further help define a region in CNF1 that is critical for full toxin binding to HEp-2 cells.