Uropathogenic Escherichia coli dominantly suppress the innate immune response of bladder epithelial cells by a lipopolysaccharide- and Toll-like receptor 4-independent pathway

Non Clinical Model to Assess the Mechanism of Action of a Combined Hyaluronic Acid, Chondroitin Sulfate and Calcium Chloride: HA+CS+CaCl2 Solution on a 3D Human Reconstructed Bladder Epithelium

Purpose

Medical Device Regulation (EU) 2017/745 requires the principal mode of action (MoA) to be demonstrated by experimental data. The MoA of Ialuril® Prefill (combined as HA+CS+CaCl2: sodium hyaluronate 1.6%, sodium chondroitin sulphate 2% w/v and calcium chloride 0.87%) Class III medical device, indicated for intravesical instillation to reduce urinary tract infections, has been evaluated on a 3D reconstructed human bladder epithelium (HBE).

Methods

Three experimental designs; i) E. coli strain selection (DSM 103538, DSM 1103) to investigate the HA+CS+CaCl2 properties in modifying bacterial growth in liquid broth (CFU 4h and 24h) at 80%, 50% and 25% concentrations; ii) evaluation of film forming properties on HBE after 15 min exposure by quantifying caffeine permeation across the epithelium; iii) capacity to counteract E. coli adhesion and biofilm formation on colonized HBE by viable counts and ultrastructural analysis by scanning electron microscopy (SEM) using ciprofloxacin as the reference antimicrobial molecule.

Results

No significant differences were observed in bacterial viability for both the E. coli strains. HA+CS+CaCl2 reduced caffeine permeation of 51.7% and 38.1% at 1h and 2h, respectively and determined a significant decrease in caffeine permeation rate at both timepoints supporting HA+CS+CaCl2 capacity to firmly adhere to the bladder epithelium creating a physical barrier on the surface. The viable counts in HBE treated tissues then infected with E. coli resulted not different from the negative control suggesting that the device did not inhibit E. coli growth. SEM images showed homogenous product distribution over the HBE surface and confirmed the capacity of HA+CS+CaCl2 to adhere to the bladder epithelium, counteracting biofilm formation.

Conclusion

The results support the capacity of HA+CS+CaCl2 to counteract bacterial invasion by using a physico-mechanical mode of action: this medical device represents a valid alternative to antibiotics in the treatment of recurrent UTIs.

SurA-like and Skp-like Proteins as Important Virulence Determinants of the Gram Negative Bacterial Pathogens

In the Gram-negative bacteria, many important virulence factors reach their destination via two-step export systems, and they must traverse the periplasmic space before reaching the outer membrane. Since these proteins must be maintained in a structure competent for transport into or across the membrane, they frequently require the assistance of chaperones. Based on the results obtained for the model bacterium Escherichia coli and related species, it is assumed that in the biogenesis of the outer membrane proteins and the periplasmic transit of secretory proteins, the SurA peptidyl-prolyl isomerase/chaperone plays a leading role, while the Skp chaperone is rather of secondary importance. However, detailed studies carried out on several other Gram-negative pathogens indicate that the importance of individual chaperones in the folding and transport processes depends on the properties of client proteins and is species-specific. Taking into account the importance of SurA functions in bacterial virulence and severity of phenotypes due to surA mutations, this folding factor is considered as a putative therapeutic target to combat microbial infections. In this review, we present recent findings regarding SurA and Skp proteins: their mechanisms of action, involvement in processes related to virulence, and perspectives to use them as therapeutic targets.

A Synthetic Peptide 2Abz23S29 Reduces Bacterial Titer and Induces Pro-Inflammatory Cytokines in a Murine Model of Urinary Tract Infection

Introduction

A urinary tract infection (UTI), which is often caused by uropathogenic E. coli (UPEC) strains, affects many people worldwide annually. UPEC causes the production of pro-inflammatory cytokines by the bladder epithelial cells; however, it has been proven that the UPEC can inhibit the early activation of the innate immune system.

Methods

This study aimed to examine the antibacterial and immunomodulatory effects of different doses of truncated alpha-defensins (human neutrophil peptide (HNP)-1) analog 2Abz²³S²⁹ on the mouse UTI model. Experimentally uropathogenic E. coli CFT073-infected mice were treated with low-dose 2Abz²³S²⁹ (250µg/mL), high-dose 2Abz²³S²⁹ (750µg/mL), ciprofloxacin (cip) (800µg/mL), or high-dose 2Abz²³S²⁹plus cip once a day 24 h post-infection. The 2Abz²³S²⁹ and cip treatment were given for two consecutive days.

Results

The in vivo results showed that fewer UPEC were recovered from the bladders of mice treated transurethrally with 2Abz²³S²⁹. Moreover, low-dose 2Abz²³S²⁹ significantly decreased the level of the interleukin-6 (IL-6), whereas high-dose 2Abz²³S²⁹ increased pro-inflammatory cytokines including IL-6, macrophage inflammatory protein/2 (MIP/2), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) in infected bladders of mice. Besides, the levels of cytokines IL-6 and MIP/2 in infected mice treated with a combination of high-dose 2Abz²³S²⁹ and cip were significantly higher than the untreated mice. In contrast, CFT073-infected mice treated with a combination of high-dose 2Abz²³S²⁹ and cip showed no changes in cytokines TNF-α and IL-1β levels, indicating that ciprofloxacin may play an anti-inflammatory role.

Conclusion

Collectively, apart from the direct antibacterial role of 2Abz²³S²⁹, our data illustrated that 2Abz²³S²⁹ modulates pro-inflammatory cytokine production of bladder in a dose-dependent manner, which has implications for the development of new anti-infective agents.

The Role of TLR4 Asp299Gly and TLR4 Thr399Ile Polymorphisms in the Pathogenesis of Urinary Tract Infections: First Evaluation in Infants and Children of Greek Origin

Urinary tract infections are one of the most common and serious bacterial infections in a pediatric population. So far, they have mainly been related to age, gender, ethnicity, socioeconomic level, and the presence of underlying anatomical or functional, congenital, or acquired abnormalities. Recently, both innate and adaptive immunities and their interaction in the pathogenesis and the development of UTIs have been studied. The aim of this study was to assess the role and the effect of the two most frequent polymorphisms of TLR4 Asp299Gly and Thr399Ile on the development of UTIs in infants and children of Greek origin. We studied 51 infants and children with at least one episode of acute urinary tract infection and 109 healthy infants and children. We found that 27.5% of patients and 8.26% of healthy children carried the heterozygote genotype for TLR4 Asp299Gly. TLR4 Thr399Ile polymorphism was found to be higher in healthy children and lower in the patient group. No homozygosity for both studied polymorphisms was detected in our patients. In the group of healthy children, a homozygote genotype for TLR4 Asp299Gly (G/G) as well as for TLR4 Thr399Ile (T/T) was showed (1.84% and 0.92 respectively). These results indicate the role of TLR4 polymorphism as a genetic risk for the development of UTIs in infants and children of Greek origin.

Some New Findings Regarding the Antiadhesive Activity of Cranberry Phenolic Compounds and Their Microbial-Derived Metabolites against Uropathogenic Bacteria

Findings concerning the antiadhesive activity of cranberry phenolic compounds and their microbial-derived metabolites against Gram-negative ( Escherichia coli ATCC 53503 and DSM 10791) and Gram-positive ( Enterococcus faecalis 04-1) bacteria in T24 cells are reported. A-Type procyanidins (A2 and cinnamtannin B-1) exhibited antiadhesive activity (at concentrations ≥250 μM), a feature that was not observed for B-type procyanidins (B2). The metabolites hippuric acid and α-hydroxyhippuric acid also showed effective results at concentrations ≥250 μM. With regard to conjugated metabolites, sulfation seemed to increase the antiadhesive activity of cranberry-derived metabolites as 3-(3,4-dihydroxyphenyl)propionic acid 3- O-sulfate presented active results, unlike its corresponding nonsulfated form. In contrast, methylation decreased antiadhesive activity as 3,4-dihydroxyphenylacetic acid was found to be active but not its corresponding methylated form (4-hydroxy-3-methoxyphenylacetic acid). As a whole, this work sustains the antiadhesive activity of cranberry-derived metabolites as one of the mechanisms involved in the beneficial effects of cranberries against urinary tract infections.

Interleukin-6/Stat3 signaling has an essential role in the host antimicrobial response to urinary tract infection

The signaling networks regulating antimicrobial activity during urinary tract infection (UTI) are incompletely understood. Interleukin-6 (IL-6) levels increase with UTI severity, but the specific contributions of IL-6 to host immunity against bacterial uropathogens are unknown. To clarify this we tested whether IL-6 activates the Stat3 transcription factor, to drive a program of antimicrobial peptide gene expression in infected urothelium during UTI. Transurethral inoculation of uropathogenic Escherichia coli led to IL-6 secretion, urothelial Stat3 phosphorylation, and activation of antimicrobial peptide transcription, in a Toll-like receptor 4-dependent manner in a murine model of cystitis. Recombinant IL-6 elicited Stat3 phosphorylation in primary urothelial cells in vitro, and systemic IL-6 administration promoted urothelial Stat3 phosphorylation and antimicrobial peptide expression in vivo. IL-6 deficiency led to decreased urothelial Stat3 phosphorylation and antimicrobial peptide mRNA expression following UTI, a finding mirrored by conditional Stat3 deletion. Deficiency in IL-6 or Stat3 was associated with increased formation of intracellular bacterial communities, and exogenous IL-6 reversed this phenotype in IL-6 knockout mice. Moreover, chronic IL-6 depletion led to increased renal bacterial burden and severe pyelonephritis in C3H/HeOuJ mice. Thus, IL-6/Stat3 signaling drives a transcriptional program of antimicrobial gene expression in infected urothelium, with key roles in limiting epithelial invasion and ascending infection.

Strain-specific inhibition of the adherence of uropathogenic bacteria to bladder cells by probiotic Lactobacillus spp

Urinary tract infections (UTIs), one of most common infections worldwide, face high recurrence rates and increasing antimicrobial resistance. Probiotic bacteria, especially of the genus Lactobacillus, are considered a promising preventive and/or treatment therapy against UTIs. In order to elucidate the mechanisms involved in these beneficial effects, we studied the impact of different Lactobacillus strains (Lactobacillus salivarius UCM572, L. plantarum CLC17 and L. acidophilus 01) in the adherence of reference and clinical uropathogenic strains (Escherichia coli ATCC® 53503, E. coli 10791, Enterococcus faecalis 04-1, En. faecalis 08-1 and Staphylococcus epidermidis 08-3) to T24 epithelial bladder cells. In general, the Lactobacillus strains with previous in vivo evidence of beneficial effects against UTIs (L. salivarius UCM572 and L. acidophilus 01) significantly inhibited the adherence of the five uropathogens to T24 cells, displaying percentages of inhibition ranging between 22.2% and 43.9%, and between 16.5% and 53.7%, respectively. On the other hand, L. plantarum CLC17, a strain with no expected effects on UTIs, showed almost negligible anti-adherence effects.Therefore, these in vitro results suggest that inhibition of the adherence of uropathogens to epithelial bladder cells may be one of the mechanisms involved in the potential beneficial effects of probiotics against UTIs in vivo.

Biofilm Formation and Immunomodulatory Activity of Proteus mirabilis Clinically Isolated Strains

Urinary tract infections (UTIs) and catheter-associated UTIs (CAUTIs) are the principal hospital-acquired infections. Proteus mirabilis is characterized by several virulence factors able to promote adhesion and biofilm formation and ameliorate the colonization of urinary tract and the formation of crystalline biofilms on the abiotic surface of the urinary catheters. Since, to date, the role of P. mirabilis in the etiopathogenesis of different types of urinary tract infections is not well established, in this study we sought to characterize two different clinically isolated strains of P. mirabilis (PM1 and PM2) with distinctive phenotypes and analyzed various virulence factors possibly implicated in the ability to induce UTIs and CAUTIs. In particular, we analyzed motility, biofilm formation both on abiotic and biotic surfaces of PM1 and PM2 and paralleled these parameters with the ability to induce an inflammatory response in an epithelial cell model. Results showed that PM1 displayed major motility and a capacity to form biofilm and was associated with an anti-inflammatory response of host cells. Conversely, PM2 exhibited lack motility and a had slower organization in biofilm but promoted an increase of proinflammatory cytokine expression in infected epithelial cells. Our study provides data useful to start uncovering the pathologic basis of P. mirabilis-associated urinary infections. The evidence of different virulence factors expressed by PM1 and PM2 highlights the possibility to use precise and personalized therapies targeting specific virulence pathways.

Subversion of Host Innate Immunity by Uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) cause the majority of community-onset urinary tract infections (UTI) and represent a major etiologic agent of healthcare-associated UTI. Introduction of UPEC into the mammalian urinary tract evokes a well-described inflammatory response, comprising pro-inflammatory cytokines and chemokines as well as cellular elements (neutrophils and macrophages). In human UTI, this inflammatory response contributes to symptomatology and provides means for diagnosis by standard clinical testing. Early in acute cystitis, as demonstrated in murine models, UPEC gains access to an intracellular niche that protects a population of replicating bacteria from arriving phagocytes. To ensure the establishment of this protected niche, UPEC employ multiple strategies to attenuate and delay the initiation of host inflammatory components, including epithelial secretion of chemoattractants. Recent work has also revealed novel mechanisms by which UPEC blunts neutrophil migration across infected uroepithelium. Taken together, these attributes distinguish UPEC from commensal and nonpathogenic E. coli strains. This review highlights the unique immune evasion and suppression strategies of this bacterial pathogen and offers directions for further study; molecular understanding of these mechanisms will inform the development of adjunctive, anti-virulence therapeutics for UTI.

A Murine Model for Escherichia coli Urinary Tract Infection

Urinary tract infections (UTI) are among the most common bacterial infections of humans. The mouse provides an excellent and tractable model system for cystitis and pyelonephritis caused by Escherichia coli and other uropathogens. Using a well-established model of experimental cystitis in which the bladders of female mice are infected via transurethral catheterization, the molecular details of the pathogenesis of bacterial cystitis have been substantially illuminated in the last decade. Uropathogenic E. coli attach to bladder epithelium (both in human and mouse) via adhesive type 1 pili, establish a replicative niche within epithelial cell cytoplasm, and form intracellular bacterial communities that are protected from antibiotic effects and immune clearance. The use of different inbred and mutant mouse strains offers the opportunity to study outcomes of infection, including resolution, formation of quiescent intracellular bacterial reservoirs, chronic bacterial cystitis, and recurrent infections. Urine, bladder, and kidney tissues can be analyzed by bacterial culture, histology, immunohistochemistry, immunofluorescent and confocal microscopy, electron microscopy, and flow cytometry, while a broad array of soluble markers (e.g., cytokines) can also be profiled in serum, urine, and tissue homogenates by ELISA, Western blotting, multiplex bead array, and other approaches. This model promises to afford continued opportunity for discovery of pathogenic mechanisms and evaluation of therapeutic and preventive strategies for acute, chronic, and recurrent UTI.

Anti-Adhesive Activity of Cranberry Phenolic Compounds and Their Microbial-Derived Metabolites against Uropathogenic Escherichia coli in Bladder Epithelial Cell Cultures

Cranberry consumption has shown prophylactic effects against urinary tract infections (UTI), although the mechanisms involved are not completely understood. In this paper, cranberry phenolic compounds and their potential microbial-derived metabolites (such as simple phenols and benzoic, phenylacetic and phenylpropionic acids) were tested for their capacity to inhibit the adherence of uropathogenic Escherichia coli (UPEC) ATCC^®53503™ to T24 epithelial bladder cells. Catechol, benzoic acid, vanillic acid, phenylacetic acid and 3,4-dihydroxyphenylacetic acid showed anti-adhesive activity against UPEC in a concentration-dependent manner from 100–500 µM, whereas procyanidin A2, widely reported as an inhibitor of UPEC adherence on uroepithelium, was only statistically significant (p < 0.05) at 500 µM (51.3% inhibition). The results proved for the first time the anti-adhesive activity of some cranberry-derived phenolic metabolites against UPEC in vitro, suggesting that their presence in the urine could reduce bacterial colonization and progression of UTI.

Uropathogenic Escherichia coli modulates innate immunity to suppress Th1-mediated inflammatory responses during infectious epididymitis

Infectious epididymitis in men, a frequent entity in urological outpatient settings, is commonly caused by bacteria originating from the anal region ascending the genitourinary tract. One of the most prevalent pathogens associated with epididymitis is Escherichia coli. In our previous study, we showed that semen quality is compromised in men following epididymitis associated with specific E. coli pathovars. Thus, our aim was to investigate possible differences in immune responses elicited during epididymitis following infection with the uropathogenic E. coli (UPEC) strain CFT073 and the nonpathogenic enteric E. coli (NPEC) strain 470. Employing an in vivo experimental epididymitis model, C57BL/6 mice were infected with UPEC CFT073, NPEC 470, or phosphate-buffered saline (PBS) as a sham control for up to 7 days. After infection with NPEC 470, the expression of proinflammatory cytokines interleukin-1 (IL-1), IL-6, and tumor necrosis factor alpha in the epididymis was significantly increased. Conversely, UPEC CFT073-challenged mice displayed inflammatory gene expression at levels comparable to sham PBS-treated animals. Moreover, by day 7 only NPEC-infected animals showed activation of adaptive immunity evident by a substantial influx of CD3+ and F4/80+ cells in the epididymal interstitium. This correlated with enhanced production of Th1-associated cytokines IL-2 and gamma interferon (IFN-γ). Furthermore, splenocytes isolated from UPEC-infected mice exhibited diminished T-cell responses with significantly reduced secretion of IL-2 and IFN-γ in contrast to NPEC-infected animals. Overall, these findings provide new insights into understanding pathogen-specific modulation of host immunity during acute phases of epididymitis, which may influence severity of disease and clinical outcomes.

Human bladder uroepithelial cells synergize with monocytes to promote IL-10 synthesis and other cytokine responses to uropathogenic Escherichia coli

Urinary tract infections are a major source of morbidity for women and the elderly, with Uropathogenic Escherichia coli (UPEC) being the most prevalent causative pathogen. Studies in recent years have defined a key anti-inflammatory role for Interleukin-10 (IL-10) in urinary tract infection mediated by UPEC and other uropathogens. We investigated the nature of the IL-10-producing interactions between UPEC and host cells by utilising a novel co-culture model that incorporated lymphocytes, mononuclear and uroepithelial cells in histotypic proportions. This co-culture model demonstrated synergistic IL-10 production effects between monocytes and uroepithelial cells following infection with UPEC. Membrane inserts were used to separate the monocyte and uroepithelial cell types during infection and revealed two synergistic IL-10 production effects based on contact-dependent and soluble interactions. Analysis of a comprehensive set of immunologically relevant biomarkers in monocyte-uroepithelial cell co-cultures highlighted that multiple cytokine, chemokine and signalling factors were also produced in a synergistic or antagonistic fashion. These results demonstrate that IL-10 responses to UPEC occur via multiple interactions between several cells types, implying a complex role for infection-related IL-10 during UTI. Development and application of the co-culture model described in this study is thus useful to define the degree of contact dependency of biomarker production to UPEC, and highlights the relevance of histotypic co-cultures in studying complex host-pathogen interactions.

Outer membrane vesicles derived from Escherichia coli up-regulate expression of endothelial cell adhesion molecules in vitro and in vivo

Escherichia coli, as one of the gut microbiota, can evoke severe inflammatory diseases including peritonitis and sepsis. Gram-negative bacteria including E. coli constitutively release nano-sized outer membrane vesicles (OMVs). Although E. coli OMVs can induce the inflammatory responses without live bacteria, the effect of E. coli OMVs in vivo on endothelial cell function has not been previously elucidated. In this study, we show that bacteria-free OMVs increased the expression of endothelial intercellular adhesion molecule-1 (ICAM-1), E-selectin and vascular cell adhesion molecule-1, and enhanced the leukocyte binding on human microvascular endothelial cells in vitro. Inhibition of NF-κB and TLR4 reduced the expression of cell adhesion molecules in vitro. OMVs given intraperitoneally to the mice induced ICAM-1 expression and neutrophil sequestration in the lung endothelium, and the effects were reduced in ICAM-1(-/-) and TLR4(-/-) mice. When compared to free lipopolysaccharide, OMVs were more potent in inducing both ICAM-1 expression as well as leukocyte adhesion in vitro, and ICAM-1 expression and neutrophil sequestration in the lungs in vivo. This study shows that OMVs potently up-regulate functional cell adhesion molecules via NF-κB- and TLR4-dependent pathways, and that OMVs are more potent than free lipopolysaccharide.

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.

Flagella from five Cronobacter species induce pro-inflammatory cytokines in macrophage derivatives from human monocytes

Cronobacter spp. are opportunistic pathogens linked to lie-threatening infections in neonates and contaminated powdered infant formula that has been epidemiologically associated with these cases. Clinical symptoms of Cronobacter include necrotizing enterocolitis, bacteremia, and meningitis. Flagella from C. sakazakii are involved in biofilm formation and its adhesion to epithelial cells. We investigated the role of flagella from C. sakazakii ST1 and ST4, C. malonaticus, C. muytjensii, C. turicensis and C. dublinensis during the activation of cytokines (IL-8, TNF-α, and IL-10) in macrophage derivatives from human monocytes, which has not been extensively studied. The production and identity of flagella from the five Cronobacter species were visualized and recognized with anti-flagella antibodies by immunogold labeling through transmission electron microscopy. Purified flagella were dissociated into monomers in 12% SDS-PAGE Coomassie blue-stained gels showing a band of ∼28 kDa and, in addition, mass spectrometry revealed the presence of several peptides that correspond to flagellin. Flagella (100 ng) induced the release of IL-8 (3314–6025 pg/ml), TNF-α (39–359 pg/ml), and IL-10 (2–96 pg/ml), in macrophage isolates from human monocytes and similar results were obtained when flagella were dissociated into monomers. Inhibition assays using three dilutions of anti-flagella antibodies (1∶10, 1∶100, and 1∶200) suppressed the secretion of IL-8, TNF-α, and IL-10 between 95–100% using 100 ng of protein. A transfection assay using 293-hTLR5 cells showed IL-8 release of 197 pg/ml and suppression in the secretion of IL-8 when anti-hTLR5-IgA antibodies were used at different concentrations. These observations suggest that flagella and flagellin are involved in an inflammatory response dependent on TLR5 recognition, which could contribute to the pathogenesis of the bacteria.

YbcL of uropathogenic Escherichia coli suppresses transepithelial neutrophil migration

Uropathogenic Escherichia coli (UPEC) strains suppress the acute inflammatory response in the urinary tract to ensure access to the intracellular uroepithelial niche that supports the propagation of infection. Our understanding of this initial cross talk between host and pathogen is incomplete. Here we report the identification of a previously uncharacterized periplasmic protein, YbcL, encoded by UPEC that contributes to immune modulation in the urinary tract by suppressing acute neutrophil migration. In contrast to wild-type UPEC, an isogenic strain lacking ybcL expression (UTI89 ΔybcL) failed to suppress transepithelial polymorphonuclear leukocyte (PMN) migration in vitro, a defect complemented by expressing ybcL episomally. YbcL homologs are present in many E. coli genomes; expression of the YbcL variant encoded by nonpathogenic E. coli K-12 strain MG1655 (YbcL(MG)) failed to complement the UTI89 ΔybcL defect, whereas expression of the UPEC YbcL variant (YbcL(UTI)) in MG1655 conferred the capacity for suppressing PMN migration. This phenotypic difference was due to a single amino acid difference (V78T) between the two YbcL homologs, and a majority of clinical UPEC strains examined were found to encode the suppressive YbcL variant. Purified YbcL(UTI) protein suppressed PMN migration in response to live or killed MG1655, and YbcL(UTI) was detected in the supernatant during UPEC infection of bladder epithelial cells or PMNs. Lastly, early PMN influx to murine bladder tissue was augmented upon in vivo infection with UTI89 ΔybcL compared with wild-type UPEC. Our findings demonstrate a role for UPEC YbcL in suppression of the innate immune response during urinary tract infection.

Expression of suppressor of cytokine signalling 3 (SOCS3) in human bladder epithelial cells infected with uropathogenic Escherichia coli

Suppressor of cytokine signalling (SOCS) proteins inhibit pro-inflammatory signalling mediated by Janus-activated kinase (JAK)-signal transducer and activator of transcription (STAT) pathways. To evade the immune response some pathogens appear to modify the host SOCS proteins. Uropathogenic Escherichia coli (UPEC) are able to subvert the host response evoked by bladder epithelial cells, but the mechanisms are not fully understood. The objective of this study was to investigate whether UPEC can modify the host SOCS and STAT3 response. Real time RT-PCR studies demonstrated an increased SOCS1 and SOCS3 expression in the isolated human bladder epithelial cell lines (RT-4 and 5637) in response to cytokines. UPEC strain IA2 increased SOCS3, but not SOCS1, mRNA levels with a peak at 6 h after infection. The increase of SOCS3 was confirmed at the protein level by Western blotting. The UPEC strain IA2 caused a time-dependent decrease in the phosphorylation of STAT3. This study demonstrates that UPEC are able to affect SOCS3 and STAT3 signalling in human uroepithelial cells. The finding that UPEC are able to induce mediators involved in suppression of host cytokine signalling may help to elucidate how UPEC may circumvent the host response during urinary tract infection.

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.

Role of Uropathogenic Escherichia coli Virulence Factors in Development of Urinary Tract Infection and Kidney Damage

Uropathogenic Escherichia coli (UPEC) is a causative agent in the vast majority of urinary tract infections (UTIs), including cystitis and pyelonephritis, and infectious complications, which may result in acute renal failure in healthy individuals as well as in renal transplant patients. UPEC expresses a multitude of virulence factors to break the inertia of the mucosal barrier. In response to the breach by UPEC into the normally sterile urinary tract, host inflammatory responses are triggered leading to cytokine production, neutrophil influx, and the exfoliation of infected bladder epithelial cells. Several signaling pathways activated during UPEC infection, including the pathways known to activate the innate immune response, interact with calcium-dependent signaling pathways. Some UPEC isolates, however, might possess strategies to delay or suppress the activation of components of the innate host response in the urinary tract. Studies published in the recent past provide new information regarding how virulence factors of uropathogenic E. coli are involved in activation of the innate host response. Despite numerous host defense mechanisms, UPEC can persist within the urinary tract and may serve as a reservoir for recurrent infections and serious complications. Presentation of the molecular details of these events is essential for development of successful strategies for prevention of human UTIs and urological complications associated with UTIs.

Escherichia coli from retail meats carry genes associated with uropathogenic Escherichia coli, but are weakly invasive in human bladder cell culture

AIMS

The aim of this study was to determine the uropathogenic potential of Escherichia coli isolated from retail meats.

METHODS AND RESULTS

Two hundred E. coli isolates recovered from retail meats, which were previously identified molecularly as extraintestinal pathogenic E. coli, were investigated for the presence of 21 uropathogenic E. coli (UPEC) virulence-associated genes. Twenty-three E. coli isolates were selected based on their serogroups and the number of virulence genes they contained, and further characterized using multilocus sequence typing, and by tissue culture assays for adherence to and invasion of T-24 human bladder cells and for their induction of interleukin (IL)-6 secretion. All virulence genes tested, except afa/dra and hlyD, were detected among the E. coli isolates. Multilocus sequence typing analysis of 23 selected isolates revealed that 17 isolates belonged to STs associated with human UPEC. Nearly all 23 isolates exhibited lower level of adherence and invasion compared to a clinical strain, UPEC CFT073.

CONCLUSIONS

These observations suggested that a small proportion of E. coli isolates from retail meats carry uropathogenic associated virulence genes and thus may serve as a reservoir of these genes to UPEC in the human intestine. Their virulence potential seemed limited as they were only weakly invasive in human bladder cell culture.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings support the hypothesis that retail meat E. coli may play a role in relation to urinary tract infection (UTI) and may be considered in development of a UTI prevention strategy.

Intracellular lifestyles and immune evasion strategies of uropathogenic Escherichia coli

Paradigms in the pathogenesis of urinary tract infections have shifted dramatically as a result of recent scientific revelations. Beyond extracellular colonization of the bladder luminal surface, as traditional clinical thinking would hold, uropathogenic bacteria direct a complex, intracellular cascade that shelters bacteria from host defenses and leads to persistent bacterial residence within the epithelium. After epithelial invasion, many organisms are promptly expelled by bladder epithelial cells; a minority establish a niche in the cytoplasm that results in the development of biofilm-like intracellular bacterial communities and serves as the primary location for bacterial expansion. Exfoliation of the superficial epithelial layer acts to reduce the bacterial load but facilitates chronic residence of small nests of bacteria that later reemerge to cause some episodes of recurrent cystitis, a familiar clinical scenario in otherwise healthy women. Advances in both in vitro and animal models of cystitis promise to provide insights into the bacterial and host transcriptional and biochemical pathways that define these pathogenic stages.

The hemorrhagic coli pilus (HCP) of Escherichia coli O157:H7 is an inducer of proinflammatory cytokine secretion in intestinal epithelial cells

Background

Enterohemorrhagic Escherichia coli (EHEC) O157:H7, the causative agent of hemorrhagic colitis and the hemolytic uremic syndrome (HUS), produces long bundles of type IV pili (TFP) called hemorrhagic coli pili (HCP). HCP are capable of mediating several phenomena associated with pathogenicity: i) adherence to human and bovine epithelial cells; ii) invasion of epithelial cells; iii) hemagglutination of rabbit erythrocytes; iv) biofilm formation; v) twitching motility; and vi) specific binding to laminin and fibronectin. HCP are composed of a 19 kDa pilin subunit (HcpA) encoded by the hcpA chromosomal gene (called prepilin peptidase-dependent gene [ppdD] in E. coli K-12).

Methodology/Principal Findings

In this study we investigated the potential role of HCP of E. coli O157:H7 strain EDL933 in activating the release of pro- and anti-inflammatory cytokines from a variety of host epithelial cells. We found that purified HCP and a recombinant HcpA protein induced significant release of IL-8 and TNF-α, from cultured polarized intestinal cells (T84 and HT-29 cells) and non-intestinal HeLa cells. Levels of proinflammatory IL-8 and TNF-α, but not IL-2, IL6, or IL-10 cytokines, were increased in the presence of HCP and recombinant HcpA after 6 h of incubation with ≥50 ng/ml of protein, suggesting that stimulation of IL-8 and TNF-α are dose and time-dependent. In addition, we also demonstrated that flagella are potent inducers of cytokine production. Furthermore, MAPK activation kinetics studies showed that EHEC induces p38 phosphorylation under HCP-producing conditions, and ERK1/2 and JNK activation was detectable after 3 h of EHEC infection. HT-29 cells were stimulated with epidermal growth factor stimulation of HT-29 cells for 30 min leading to activation of three MAPKs.

Conclusions/Significance

The HcpA pilin monomer of the HCP produced by EHEC O157:H7 is a potent inducer of IL-8 and TNF-α release, an event which could play a significant role in the pathogenesis of hemorrhagic colitis caused by this pathogen.

Safety of probiotic Escherichia coli strain Nissle 1917 depends on intestinal microbiota and adaptive immunity of the host

Probiotics are viable microorganisms that are increasingly used for treatment of a variety of diseases. Occasionally, however, probiotics may have adverse clinical effects, including septicemia. Here we examined the role of the intestinal microbiota and the adaptive immune system in preventing translocation of probiotics (e.g., Escherichia coli Nissle). We challenged C57BL/6J mice raised under germfree conditions (GF-raised C57BL/6J mice) and Rag1(-/-) mice raised under germfree conditions (GF-raised Rag1(-/-) mice) and under specific-pathogen-free conditions (SPF-raised Rag1(-/-) mice) with probiotic E. coli strain Nissle 1917, strain Nissle 1917 mutants, the commensal strain E. coli mpk, or Bacteroides vulgatus mpk. Additionally, we reconstituted Rag1(-/-) mice with CD4(+) T cells. E. coli translocation and dissemination and the mortality of mice were assessed. In GF-raised Rag1(-/-) mice, but not in SPF-raised Rag1(-/-) mice or GF-raised C57BL/6J mice, oral challenge with E. coli strain Nissle 1917, but not oral challenge with E. coli mpk, resulted in translocation and dissemination. The mortality rate was significantly higher for E. coli strain Nissle 1917-challenged GF-raised Rag1(-/-) mice (100%; P < 0.001) than for E. coli strain Nissle 1917-challenged SPF-raised Rag1(-/-) mice (0%) and GF-raised C57BL/6J mice (0%). Translocation of and mortality due to strain E. coli Nissle 1917 in GF-raised Rag1(-/-) mice were prevented when mice were reconstituted with T cells prior to strain E. coli Nissle 1917 challenge, but not when mice were reconstituted with T cells after E. coli strain Nissle 1917 challenge. Cocolonization experiments revealed that E. coli mpk could not prevent translocation of strain E. coli Nissle 1917. Moreover, we demonstrated that neither lipopolysaccharide structure nor flagella play a role in E. coli strain Nissle 1917 translocation and dissemination. Our results suggest that if both the microbiota and adaptive immunity are defective, translocation across the intestinal epithelium and dissemination of the probiotic E. coli strain Nissle 1917 may occur and have potentially severe adverse effects. Future work should define the possibly related molecular factors that promote probiotic functions, fitness, and facultative pathogenicity.

Uropathogenic Escherichia coli Suppresses the host inflammatory response via pathogenicity island genes sisA and sisB

Extraintestinal pathogenic Escherichia coli can successfully colonize the urinary tract of the immunocompetent host. In part, this is accomplished by dampening the host immune response. Indeed, the sisA and sisB genes (shiA-like inflammation suppressor genes A and B) of uropathogenic E. coli strain CFT073, homologs of the Shigella flexneri SHI-2 pathogenicity island gene shiA, suppress the host inflammatory response. A double deletion mutant (DeltasisA DeltasisB) resulted in a hyperinflammatory phenotype in an experimental model of ascending urinary tract infection. The DeltasisA DeltasisB mutant not only caused significantly more inflammatory foci in the kidneys of CBA/J mice (P = 0.0399), but these lesions were also histologically more severe (P = 0.0477) than lesions observed in mice infected with wild-type CFT073. This hyperinflammatory phenotype could be suppressed to wild-type levels by in vivo complementation of the DeltasisA DeltasisB mutant with either the sisA or sisB gene in trans. The DeltasisA DeltasisB mutant was outcompeted by wild-type CFT073 during cochallenge infection in the bladder (P = 0.0295) at 48 h postinoculation (hpi). However, during cochallenge infections, we reasoned that wild-type CFT073 could partially complement the DeltasisA DeltasisB mutant. Consistent with this, the most significant colonization defect of the DeltasisA DeltasisB mutant in vivo was observed during independent challenge relative to wild-type CFT073, with attenuation of the mutant observed in the bladder (P < 0.0001) and kidneys (P = 0.0003) at 6 hpi. By 24 and 48 hpi, the DeltasisA DeltasisB mutant was no longer significantly attenuated in the bladder or kidneys, suggesting that the sisA and sisB genes may be important for suppressing the host immune response during the initial stages of infection.

Rapid isolation of HSV-1 and HSV-2 from OneSwab cervicovaginal specimens

Herpes simplex viruses are significant human pathogens which remain latent in their hosts for life and reactivate to cause disease at or near the initial site of infection. Since HSV infections are associated with high morbidity, rapid detection and diagnosis of these viruses is imperative. While PCR technology for the diagnosis of HSV is now almost utilized universally, virus isolation from mucosa and skin in shell cultures is still applied in many clinical settings. Virus growth in cultured cells alone has the disadvantage that it cannot distinguish between HSV-1 and HSV-2. The aim of this study was to combine these two disparate methods. A protocol was developed to isolate clinical strains directly from the medium used for as the standard source of extraction to isolate DNA. Both HSV-1 and HSV-2 strains were isolated successfully from cervicovaginal swabs transported in OneSwab devices. It was found that the titers of these viruses did not correlate with the C(T) scores determined for the samples using real-time PCR. HSV-2 strains generally had lower titers than those of HSV-1, suggesting that the HSV-2 may be more sensitive to the sample handling procedures. These studies represent the first report of the culture and isolation of HSV from clinical samples using OneSwab intended exclusively for molecular diagnostic analyses.

Molecular basis of uropathogenic Escherichia coli evasion of the innate immune response in the bladder

In the urinary tract, the innate immune system detects conserved bacterial components and responds to infection by activating the proinflammatory transcription factor NF-kappaB, resulting in cytokine secretion and neutrophil recruitment. Uropathogenic Escherichia coli (UPEC), however, has been shown to evade the host innate immune response by suppressing NF-kappaB activation in urothelial cells, which results in decreased cytokine secretion and increased urothelial apoptosis. To understand the molecular basis of UPEC modulation of inflammation, we performed a genetic screen with UPEC strain NU14 to identify genes which are required for modulation of urothelial cytokine secretion. Disruption of ampG (peptidoglycan permease), waaL (lipopolysaccharide O antigen ligase), or alr (alanine racemase) resulted in increased urothelial interleukin-8 (IL-8) and IL-6 release from urothelial cell cultures. Targeted deletion of these genes also resulted in elevated urothelial cytokine production during UPEC infection. Conditioned media from bacterial cultures of NU14 DeltaampG and NU14 DeltawaaL contained a heat-stable factor(s) which stimulated greater urothelial IL-8 secretion than that in NU14-conditioned medium. In a mouse model of urinary tract infection, NU14 DeltaampG, NU14 DeltawaaL, and NU14 Deltaalr were attenuated compared to wild-type NU14 and showed reduced fitness in competition experiments. Instillation of NU14 DeltaampG or NU14 DeltawaaL increased bladder neutrophil recruitment, indicating that enhanced urothelial cytokine secretion during urinary tract infection results in an altered host response. Thus, UPEC evasion of innate immune detection of bacterial components, such as lipopolysaccharide and peptidoglycan fragments, is likely an important factor in the ability of UPEC to colonize the urinary tract.