P fimbriae-dependent, lipopolysaccharide-independent activation of epithelial cytokine responses

High Biofilm-Forming Multidrug-Resistant Salmonella Infantis Strains from the Poultry Production Chain

The ability of Salmonella species to adhere to surfaces and form biofilms, leading to persistent environmental reservoirs, might represent a direct link between environmental contamination and food processing contamination. The purpose of this study was to investigate the biofilm-forming ability of 80 multidrug-resistant (MDR) and extended-spectrum beta-lactamase (ESBL) producing Salmonella enterica serovar Infantis strains isolated from the broiler food chain production through whole genome sequencing (WGS), PCR, and morphotype association assays. Biofilm formation was quantified by testing the strains at two different temperatures, using 96-well polystyrene plates. The rough and dry colony (rdar) morphotype was assessed visually on Congo red agar (CRA) plates. Based on our results, all tested S. Infantis strains produced biofilm at 22 °C with an rdar morphotype, while at 37 °C, all the isolates tested negative, except one positive. Most isolates (58.75%) exhibited strong biofilm production, while 36.25% showed moderate production. Only 5 out of 80 (6.25%) were weak biofilm producers. WGS analysis showed the presence of the fim cluster (fimADF) and the csg cluster (csgBAC and csgDEFG), also described in S. Typhimurium, which are responsible for fimbriae production. PCR demonstrated the presence of csgD, csgB, and fimA in all 80 S. Infantis strains. To our knowledge, this is the first study comparing the effects of two different temperatures on the biofilm formation capacity of ESBL producing S. Infantis from the broiler production chain. This study highlights that the initial biofilm components, such as curli and cellulose, are specifically expressed at lower temperatures. It is important to emphasize that within the broiler farm, the environmental temperature ranges between 18-22 °C, which is the optimum temperature for in vitro biofilm formation by Salmonella spp. This temperature range facilitates the expression of biofilm-associated genes, contributing to the persistence of S. Infantis in the environment. This complicates biosecurity measures and makes disinfection protocols on the farm and in the production chain more difficult, posing serious public health concerns.

Polysaccharides from Vaccaria segetalis seeds reduce urinary tract infections by inhibiting the adhesion and invasion abilities of uropathogenic Escherichia coli

The seeds of Vaccaria segetalis (Neck.) are from a traditional medicinal plant Garcke, also called Wang-Bu-Liu-Xing in China. According to the Chinese Pharmacopoeia, the seeds of V. segetalis can be used for treating urinary system diseases. This study was designed to investigate the underlying mechanism of VSP (polysaccharides from Vaccaria segetalis) against urinary tract infections caused by uropathogenic Escherichia coli (UPEC). Here, both in vitro and in vivo infection models were established with the UPEC strain CFT073. Bacterial adhesion and invasion into bladder epithelial cells were analyzed. We found that VSP reduced the adhesion of UPEC to the host by inhibiting the expression of bacterial hair follicle adhesion genes. VSP also reduced the invasion of UPEC by regulating the uroplakins and Toll-like receptors of host epithelial cells. In addition, the swarming motility and flagella-mediated motility genes flhC, flhD and Flic of UPEC were diminished after VSP intervention. Taken together, our findings reveal a possible mechanism by which VSP interferes with the adhesion and invasion of UPEC.

Protective vascular coagulation in response to bacterial infection of the kidney is regulated by bacterial lipid A and host CD147

Bacterial infection of the kidney leads to a rapid cascade of host protective responses, many of which are still poorly understood. We have previously shown that following kidney infection with uropathogenic Escherichia coli (UPEC), vascular coagulation is quickly initiated in local perivascular capillaries that protects the host from progressing from a local infection to systemic sepsis. The signaling mechanisms behind this response have not however been described. In this study, we use a number of in vitro and in vivo techniques, including intravital microscopy, to identify two previously unrecognized components influencing this protective coagulation response. The acylation state of the Lipid A of UPEC lipopolysaccharide (LPS) is shown to alter the kinetics of local coagulation onset in vivo. We also identify epithelial CD147 as a potential host factor influencing infection-mediated coagulation. CD147 is expressed by renal proximal epithelial cells infected with UPEC, contingent to bacterial expression of the α-hemolysin toxin. The epithelial CD147 subsequently can activate tissue factor on endothelial cells, a primary step in the coagulation cascade. This study emphasizes the rapid, multifaceted response of the kidney tissue to bacterial infection and the interplay between host and pathogen during the early hours of renal infection.

Pili Assembled by the Chaperone/Usher Pathway in Escherichia coli and Salmonella

Gram-negative bacteria assemble a variety of surface structures, including the hair-like organelles known as pili or fimbriae. Pili typically function in adhesion and mediate interactions with various surfaces, with other bacteria, and with other types of cells such as host cells. The chaperone/usher (CU) pathway assembles a widespread class of adhesive and virulence-associated pili. Pilus biogenesis by the CU pathway requires a dedicated periplasmic chaperone and integral outer membrane protein termed the usher, which forms a multifunctional assembly and secretion platform. This review addresses the molecular and biochemical aspects of the CU pathway in detail, focusing on the type 1 and P pili expressed by uropathogenic Escherichia coli as model systems. We provide an overview of representative CU pili expressed by E. coli and Salmonella, and conclude with a discussion of potential approaches to develop antivirulence therapeutics that interfere with pilus assembly or function.

Urinary Tract Infection Molecular Mechanisms and Clinical Translation

Rapid developments in infection biology create new and exciting options for individualized diagnostics and therapy. Such new practices are needed to improve patient survival and reduce morbidity. Molecular determinants of host resistance to infection are being characterized, making it possible to identify susceptible individuals and to predict their risk for future morbidity. Immunotherapy is emerging as a new strategy to treat infections worldwide and controlled boosting of the host immune defense represents an important therapeutic alternative to antibiotics. In proof of concept studies, we have demonstrated that this approach is feasible. The long-term goal is not just to remove the pathogens but to also develop technologies that restore resistance to infection in disease-prone patients and devise personalized therapeutic interventions. Here, we discuss some approaches to reaching these goals, in patients with urinary tract infection (UTI). We describe critical host signaling pathways that define symptoms and pathology and the genetic control of innate immune responses that balance protection against tissue damage. For some of these genes, human relevance has been documented in clinical studies, identifying them as potential targets for immune-modulatory therapies, as a complement to antibiotics.

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

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

Uropathogenic Escherichia coli Engages CD14-Dependent Signaling to Enable Bladder-Macrophage-Dependent Control of Acute Urinary Tract Infection

BACKGROUND

CD14, a coreceptor for several pattern recognition receptors and a widely used monocyte/macrophage marker, plays a key role in host responses to gram-negative bacteria. Despite the central role of CD14 in the inflammatory response to lipopolysaccharide and other microbial products and in the dissemination of bacteria in some infections, the signaling networks controlled by CD14 during urinary tract infection (UTI) are unknown.

METHODS

We used uropathogenic Escherichia coli (UPEC) infection of wild-type (WT) C57BL/6 and Cd14(-/-) mice and RNA sequencing to define the CD14-dependent transcriptional signature and the role of CD14 in host defense against UTI in the bladder.

RESULTS

UPEC induced the upregulation of Cd14 and the monocyte/macrophage-related genes Emr1/F4/80 and Csf1r/c-fms, which was associated with lower UPEC burdens in WT mice, compared with Cd14(-/-) mice. Exacerbation of infection in Cd14(-/-) mice was associated with the absence of a 491-gene transcriptional signature in the bladder that encompassed multiple host networks not previously associated with this receptor. CD14-dependent pathways included immune cell trafficking, differential cytokine production in macrophages, and interleukin 17 signaling. Depletion of monocytes/macrophages in the bladder by administration of liposomal clodronate led to higher UPEC burdens.

CONCLUSIONS

This study identifies new host protective and signaling roles for CD14 in the bladder during UPEC UTI.

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.

Epithelial Cells Secrete Interleukin-8 in Response to Adhesion and Invasion of Diffusely AdheringEscherichia coliLacking Afa/Dr Genes

Escherichia coli that sparsely adhere to human epithelial cells are known as diffusely adherent E. coli (DAEC), and the role of the Afa/Dr family of adhesins is now understood. Strains that do not possess Afa/Dr, however, comprise another group of DAEC, of which the pathogenicity remains unknown. The ability to induce interleukin-8 (IL-8) secretion from intestinal epithelial cells might be a feature of enterovirulent bacteria. We previously found that some Afa/Dr DAEC strains induce IL-8 by stimulating epithelial cells with flagella. The present study examines whether non-Afa/Dr DAEC can induce IL-8 in epithelial cells (HEp-2, INT407, and T84). Among 21 strains, 11 (52%; 11/21) induced as much IL-8 as high inducer strains of Afa/Dr DAEC. Adhesion did not significantly differ between high and low inducers; therefore diffuse adhesion alone is probably insufficient to induce IL-8. It was shown that IL-8 induction and the number of intracellular bacteria directly correlated. Wortmannin, an inhibitor of the phosphatidylinositol-3-phosphate kinase, reduced both intracellular bacteria and IL-8 secretion. Motile strains were significantly more prevalent among high (10/11) than low (4/10) inducers. However, 4 low invasive strains hardly induced IL-8 despite their motility. In conclusion, some non-Afa/Dr DAEC invoke the induction of high levels of inflammatory cytokines. Unlike Afa/Dr DAEC, however, non-Afa/Dr strains may require invasion to cause strong induction. These non-Afa/Dr high inducers can be enteropathogenic for the cytokine-inducing properties.

Susceptibility to acute pyelonephritis or asymptomatic bacteriuria: host-pathogen interaction in urinary tract infections

Our knowledge of the molecular mechanisms of urinary tract infection (UTI) pathogenesis has advanced greatly in recent years. In this review, we provide a general background of UTI pathogenesis, followed by an update on the mechanisms of UTI susceptibility, with a particular focus on genetic variation affecting innate immunity. The innate immune response of the host is critically important in the antibacterial defence mechanisms of the urinary tract, and bacterial clearance normally proceeds without sequelae. However, slight dysfunctions in these mechanisms may result in acute disease and tissue destruction. The symptoms of acute pyelonephritis are caused by the innate immune response, and inflammation in the urinary tract decreases renal tubular function and may give rise to renal scarring, especially in paediatric patients. In contrast, in children with asymptomatic bacteriuria (ABU), bacteria persist without causing symptoms or pathology. Pathogenic agents trigger a response determined by their virulence factors, mediating adherence to the urinary tract mucosa, signalling through Toll-like receptors (TLRs) and activating the defence mechanisms. In ABU strains, such virulence factors are mostly not expressed. However, the influence of the host on UTI severity cannot be overestimated, and rapid progress is being made in clarifying host susceptibility mechanisms. For example, genetic alterations that reduce TLR4 function are associated with ABU, while polymorphisms reducing IRF3 or CXCR1 expression are associated with acute pyelonephritis and an increased risk for renal scarring. It should be plausible to "individualize" diagnosis and therapy by combining information on bacterial virulence and the host response.

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.

BarA-UvrY two-component system regulates virulence of uropathogenic E. coli CFT073

Uropathogenic Escherichia coli (UPEC), a member of extraintestinal pathogenic E. coli, cause ∼80% of community-acquired urinary tract infections (UTI) in humans. UPEC initiates its colonization in epithelial cells lining the urinary tract with a complicated life cycle, replicating and persisting in intracellular and extracellular niches. Consequently, UPEC causes cystitis and more severe form of pyelonephritis. To further understand the virulence characteristics of UPEC, we investigated the roles of BarA-UvrY two-component system (TCS) in regulating UPEC virulence. Our results showed that mutation of BarA-UvrY TCS significantly decreased the virulence of UPEC CFT073, as assessed by mouse urinary tract infection, chicken embryo killing assay, and cytotoxicity assay on human kidney and uroepithelial cell lines. Furthermore, mutation of either barA or uvrY gene reduced the production of hemolysin, lipopolysaccharide (LPS), proinflammatory cytokines (TNF-α and IL-6) and chemokine (IL-8). The virulence phenotype was restored similar to that of wild-type by complementation of either barA or uvrY gene in trans. In addition, we discussed a possible link between the BarA-UvrY TCS and CsrA in positively and negatively controlling virulence in UPEC. Overall, this study provides the evidences for BarA-UvrY TCS regulates the virulence of UPEC CFT073 and may point to mechanisms by which virulence regulations are observed in different ways may control the long-term survival of UPEC in the urinary tract.

Genetics of innate immunity and UTI susceptibility

A functional and well-balanced immune response is required to resist most infections. Slight dysfunctions in innate immunity can turn the 'friendly' host defense into an unpleasant foe and give rise to disease. Beneficial and destructive forces of innate immunity have been discovered in the urinary tract and mechanisms by which they influence the severity of urinary tract infections (UTIs) have been elucidated. By modifying specific aspects of the innate immune response to UTI, genetic variation either exaggerates the severity of acute pyelonephritis to include urosepsis and renal scarring or protects against symptomatic disease by suppressing innate immune signaling, as in asymptomatic bacteriuria (ABU). Different genes are polymorphic in patients prone to acute pyelonephritis or ABU, respectively, and yet discussions of UTI susceptibility in clinical practice still focus mainly on social and behavioral factors or dysfunctional voiding. Is it not time for UTIs to enter the era of molecular medicine? Defining why certain individuals are protected from UTI while others have severe, recurrent infections has long been difficult, but progress is now being made, encouraging new approaches to risk assessment and therapy in this large and important patient group, as well as revealing promising facets of 'good' versus 'bad' inflammation.

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.

Waging war against uropathogenic Escherichia coli: winning back the urinary tract

Urinary tract infection (UTI) caused by uropathogenic Escherichia coli (UPEC) is a substantial economic and societal burden-a formidable public health issue. Symptomatic UTI causes significant discomfort in infected patients, results in lost productivity, predisposes individuals to more serious infections, and usually necessitates antibiotic therapy. There is no licensed vaccine available for prevention of UTI in humans in the United States, likely due to the challenge of targeting a relatively heterogeneous group of pathogenic strains in a unique physiological niche. Despite significant advances in the understanding of UPEC biology, mechanistic details regarding the host response to UTI and full comprehension of genetic loci that influence susceptibility require additional work. Currently, there is an appreciation for the role of classic innate immune responses-from pattern receptor recognition to recruitment of phagocytic cells-that occur during UPEC-mediated UTI. There is, however, a clear disconnect regarding how factors involved in the innate immune response to UPEC stimulate acquired immunity that facilitates enhanced clearance upon reinfection. Unraveling the molecular details of this process is vital in the development of a successful vaccine for prevention of human UTI. Here, we survey the current understanding of host responses to UPEC-mediated UTI with an eye on molecular and cellular factors whose activity may be harnessed by a vaccine that stimulates lasting and sterilizing immunity.

Pore-forming toxins activate MAPK p38 by causing loss of cellular potassium

Mitogen activated protein kinase (MAPK) p38 has emerged as a survival protein in cells that are attacked by bacterial toxins forming small membrane pores. Activation of p38 by pore forming toxins (PFT) has been attributed to osmotic stress, but here we show that loss of K+ is likely to be the critical parameter. Several lines of evidence support this conclusion: first, osmoprotection did not prevent p38-phosphorylation in alpha-toxin-loaded cells. Second, treatment of cells with a K+ ionophore, or simple incubation in K+-free medium sufficed to cause robust p38-phosphorylation. Third, media containing high [K+] prevented p38-activation by Staphylococcus aureus alpha-toxin, Vibrio cholerae cytolysin (VCC), Streptolysin O (SLO), or Escherichia coli hemolysin (HlyA), but did not impair activation by H2O2. Fourth, potential roles of LPS, TLR4, or calcium-influx were ruled out. Therefore, we propose that PFT trigger the p38 MAPK-pathway by causing loss of cellular K+.

Treponema denticola does not induce production of common innate immune mediators from primary gingival epithelial cells

It has been hypothesized that the neutrophil chemoattractant interleukin-8 (IL-8) forms a gradient in the oral cavity, with the highest concentration of IL-8 produced closest to the bacterial biofilm. In periodontitis, this gradient is disrupted, impairing neutrophil chemotaxis to diseased sites. Treponema denticola is prominently associated with periodontal disease, yet little is known about its ability to modulate the production of inflammatory mediators by epithelial cells. Others have shown that dentilisin, the major outer membrane protease of T. denticola, degrades IL-8 in vitro. We now provide evidence that T. denticola also fails to induce IL-8 production from primary gingival epithelial cells (PGEC). The lack of IL-8 production is not explained by IL-8 degradation, because a protease mutant that does not degrade IL-8 does not induce IL-8 production with these stimuli either. The lack of innate immune mediator production may be a more global phenomenon because T. denticola fails to induce IL-6 or intercellular adhesion molecule 1 production from PGEC. T. denticola also fails to induce transcription of IL-8 and human beta-defensin-2 messenger RNA. The lack of immune mediator production is not explained by the failure of T. denticola to interact with Toll-like receptor 2 (TLR-2), as T. denticola stimulates nuclear factor-kappaB nuclear translocation in TLR-2-transfected HEK293 cells. Not only can T. denticola degrade the IL-8 present in the periodontal lesion, but this organism also fails to induce IL-8 production by PGEC. The lack of an epithelial cell response to T. denticola may contribute to the pathogenesis of periodontitis by failing to trigger chemotaxis of neutrophils into the periodontal pocket.

TLR- and CXCR1-dependent innate immunity: insights into the genetics of urinary tract infections

The susceptibility to urinary tract infection (UTI) is controlled by the innate immune response and Toll like receptors (TLRs) are the sentinels of this response. If productive, TLR4 signalling may initiate the symptomatic disease process. In the absence of TLR4 signalling the infected host instead develops an asymptomatic carrier state. The activation of mucosal TLR4 is also influenced by the properties of the infecting strain, and pathogens use their virulence factors to trigger 'pathogen-specific' TLR4 responses in the urinary tract but do not respond to the asymptomatic carrier strains in patients with asymptomatic bacteriuria (ABU). The TLR4 dependence has been demonstrated in mice and the relevance of low TLR4 function for protection for human disease was recently confirmed in children with asymptomatic bacteriuria, who expressed less TLR4 than age matched controls. Functional chemokines and functional chemokine receptors are crucial for neutrophil recruitment, and for the neutrophil dependent bacterial clearance. Interleukin (IL)-8 receptor deficient mice develop acute septic infections and chronic tissue damage, due to aberrant neutrophil function. This mechanism is relevant for human UTI as pyelonephritis prone children express low levels of the human CXCL8 (Il-8) receptor, CXC chemokine receptor 1 (CXCR1) and often have heterozygous CXCR1 polymorphisms. This review illustrates how intimately the innate response and the susceptibility to UTI are linked and sophisticated recognition mechanisms that rely on microbial virulence and on host TLR4 and CXCR1 signalling.

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

Urinary tract infections are a major source of morbidity among women, with the majority caused by uropathogenic Escherichia coli. Our objective was to test if uropathogenic E. coli suppress the innate immune response of bladder epithelial cells. We found that bladder epithelial cells secrete interleukin-6 and interleukin-8 in response to non-pathogenic E. coli, whereas they failed to do so in response to uropathogenic E. coli. Uropathogenic E. coli prevented interleukin-6 secretion in response to non-pathogenic E. coli and a panel of Toll-like receptor agonists, as well as to interleukin-1beta, but not to tumor necrosis factor alpha. These results indicate that receptors with a Toll/interleukin-1 receptor domain are specifically targeted, and that suppression is not a consequence of toxicity. One candidate for mediating immune suppression is bacterial lipopolysaccharide. However, lipopolysaccharide isolated from either uropathogenic or non-pathogenic E. coli stimulated interleukin-6 secretion to similar levels. In addition, uropathogenic E. coli did not stimulate interleukin-6 secretion from cells expressing a dominant negative Toll-like receptor 4, and prevented cells lacking Toll-like receptor 4 from secreting interleukin-6 in response to synthetic lipoprotein. We conclude that uropathogenic E. coli suppress the innate immune response through a pathway partially independent of lipopolysaccharide and Toll-like receptor 4.

Urinary tract infections revisited

Urinary tract infections (UTIs) remain a significant clinical problem, despite antibiotic treatment and surgical correction of reflux and malformations. Here we propose that novel molecular tools may be applied to modernize and individualize the diagnosis and therapy of UTI. Determinants of bacterial virulence and host resistance are relatively well understood at the molecular level, and technology for their detection is within reach.

Fimbrial lectins influence the chemokine repertoire in the urinary tract mucosa

The defense against mucosal infections relies on chemokines that recruit inflammatory cells to the mucosa. This study examined if the chemokine response to uro-pathogenic Escherichia coli is influenced by fimbrial expression. The CXC (CXCL1, CXCL5, CXCL8, CXCL9, CXCL10) and CC chemokines (CCL2, CCL3, CCL5) were quantified after in vitro infection of uro-epithelial cells with a fimbriated E. coli pyelonephritis isolate, or with P or type 1 fimbriated transformants of an avirulent E. coli K-12 strain. The response profile was shown to vary with the fimbrial type. Type 1 fimbriated E. coli elicited mainly CXCL1 and CXCL8, whereas P fimbriated E. coli stimulated CCL2 and CCL5 and class II were more potent chemokine inducers than class III P fimbriae. Chemokines were also quantified in urine samples from 73 patients with febrile urinary tract infection, and analyzed as a function of disease severity and fimbrial expression by the strain infecting each patient. A complex CXC and CC chemokine response was detected in patient urine, with a significant influence of the fimbrial type. The results show that virulence factors like fimbriae may modify the mucosal chemokine response. This mechanism may allow the host to adjust the inflammatory cell infiltrate to fit the infecting strain.

Ceramide as a TLR4 agonist; a putative signalling intermediate between sphingolipid receptors for microbial ligands and TLR4

Mucosal Toll-like receptors (TLRs) respond to pathogens, but remain inert to the indigenous flora, suggesting that the TLRs can receive pathogen-specific signals. For example, TLR4 signalling is activated in CD14-negative epithelial cells by P-fimbriated, uropathogenic Escherichia coli, but not by lipopolysaccharide. The fimbriae use glycosphingolipids as recognition receptors and there is release of ceramide, which is the membrane-anchoring domain of the receptors. In this study, ceramide was identified as a TLR4 agonist and as a putative signalling intermediate between the glycosphingolipid recognition receptors and TLR4. Exogenous ceramide activated a TLR4-dependent epithelial cell response, as shown by exposing stably transfected TLR4-positive or -negative human embryonal kidney cells to C2 and C6 ceramide. A similar, TLR4-dependent response occurred after deliberate release of endogenous long-chained ceramide with sphingomyelinase. Microbial ligands with glycosphingolipid specificity (P fimbriae or the B subunit of Shiga toxin) were shown to increase the levels of ceramide and to trigger a TLR4-dependent response in epithelial cells. The results show that ceramide activates TLR4 signalling and suggest that this mechanism might allow pathogens to elicit mucosal TLR4 responses by perturbing sphingolipid receptors for virulence ligands like P fimbriae.

MarA, SoxS and Rob function as virulence factors in an Escherichia coli murine model of ascending pyelonephritis

MarA, SoxS and Rob are transcription factors belonging to the AraC family. While these proteins have been associated historically with control of multiple antibiotic resistance, and tolerance to oxidative stress agents and organic solvents, only a paucity of experimental data support a role in regulating virulence. Clinical Escherichia coli isolates, and isogenic strains lacking marA, soxS and rob, were studied in a murine model of ascending pyelonephritis, which is a clinically relevant model of urinary tract infection. Organisms lacking all three transcription factors (triple knockouts) were significantly less virulent than parental strains, and complementation studies demonstrated that the addition of marA, soxS and rob individually restored wild-type virulence in the triple-knockout strain. Deletion of soxS or rob alone was more detrimental than the removal of marA. Thus, all three proteins contribute to virulence in vivo.

Urinary tract infection in women: New pathogenic considerations

Urinary tract infection (UTI) is a common clinical syndrome in women. Most UTIs are caused by Escherichia coli. UTI has become a productive and accessible model system for studying the molecular details of how bacteria interact with mucosal surfaces and the nature of the host response. Important advances in the past year include the discovery of new virulence determinants; better understanding the pathogenic role of the ubiquitous motility organelle, the flagellum; and defining aspects of coordinate regulation of virulence determinants in the pathogenesis of UTI.

Renal allograft injury is associated with urinary tract infection caused by Escherichia coli bearing adherence factors

Urinary tract infections are the most common infection in renal transplant patients and Escherichia coli (E. coli) is the most common clinical isolate. Although acute allograft injury (AAI) secondary to urinary tract infection (UTI) has been reported, the incidence of AAI associated with UTI, the virulence factors express by uropathic E. coli and whether virulence factors are associated with renal allograft outcome have not been described. We collected E. coli from our renal transplant patients with UTI, determined O:H serotypes, P and Dr fimbriae expression and the clinical presentation and allograft function during the UTI and post-UTI period. Pyelonephritis occurred in 40% of our patients, 82% of which had AAI (>20% increase in SCr). Sixty-two percent of E. coli isolates that expressed P fimbriae were associated with AAI, whereas only 29% that did not express P fimbriae had AAI (p = 0.03). The pattern of P fimbriae and O serotypes differed from reported isolates, as the P fimbriae PapG class II and the O25 serotype were the most common. Dr adhesin was expressed on 7 isolates, including 2 of 3 with urosepsis. We propose a unique pattern of uropathogenic serotypes and adherence factors contribute to acute allograft injury in renal transplant patients with UTI.

Toll-like receptors TLR2 and TLR4 initiate the innate immune response of the renal tubular epithelium to bacterial products

Renal tubular epithelial cells (TECs) respond diffusely to local infection, with the release of multiple cytokines, chemokines and other factors that are thought to orchestrate the cellular constituents of the innate immune response. We have investigated whether the Toll-like receptors TLR4 and TLR2, which are present on tubular epithelium and potentially detect a range of bacterial components, co-ordinate this inflammatory response acting through nuclear factor-kappa B (NF-kappaB). Primary cultures of TECs were grown from C57BL/6, C3H/HeN, C3H/HeJ, TLR2 and TLR4 knock-out mice. Cell monolayers were stimulated with lipopolysaccharide (LPS) and synthetic TLR2 and 4 agonists. The innate immune response was quantified by measurement of the cytokines tumour necrosis factor (TNF)-alpha and KC (IL-8 homologue) in cell supernatants by enzyme-linked immunosorbent assay. Cultured TECs grown from healthy mice produced the cytokines TNF-alpha and KC in response to stimulation by LPS and synthetic TLR2 and TLR4 agonists. Cells lacking the respective TLRs had a reduced response to stimulation. The TLR2- and TLR4-mediated response to stimulation was dependent on NF-kappaB signalling, as shown by curcumin pretreatment of TECs. Finally, apical stimulation of these TLRs elicited basal surface secretion of TNF-alpha and KC (as well as the reverse), consistent with the biological response in vivo. Our data highlight the potential importance of TLR-dependent mechanisms co-ordinating the innate immune response to upper urinary tract infection.

Demonstration of regulatory cross-talk between P fimbriae and type 1 fimbriae in uropathogenic Escherichia coli

The majority of Escherichia coli strains isolated from urinary tract infections have the potential to express multiple fimbriae. Two of the most common fimbrial adhesins are type 1 fimbriae and pyelonephritis-associated pili (Pap). Previous research has shown that induced, plasmid-based expression of a Pap regulator, papB, and its close homologues can prevent inversion of the fim switch controlling the expression of type 1 fimbriae. The aim of the present study was to determine if this cross-regulation occurs when PapB is expressed from its native promoter in the chromosome of E. coli K-12 and clinical isolates. The regulation was examined in three ways: (1) mutated alleles of the pap regulatory region, including papB and papI, that maintain the pap promoter in either the off or the on phase were exchanged into the chromosome of both E. coli K-12 and the clinical isolate E. coli CFT073, and the effect on type 1 fimbrial expression was measured; (2) type 1 fimbrial expression was determined using a novel fimS : : gfp(+) reporter system in mutants of the clinical isolate E. coli 536 in which combinations of complete fimbrial clusters had been deleted; (3) type 1 fimbrial expression was determined in a range of clinical isolates and compared with both the number of P clusters and their expression. All three approaches demonstrated that P expression represses type 1 fimbrial expression. Using a number of novel genetic approaches, this work extends the initial finding that PapB inhibits FimB recombination to the impact of this regulation in clinical isolates.

Prostasin attenuates inducible nitric oxide synthase expression in lipopolysaccharide-induced urinary bladder inflammation

Prostasin is a glycosylphosphatidylinositol-anchored serine protease, with epithelial sodium channel activation and tumor invasion suppression activities. We identified the bladder as an expression site of prostasin. In the mouse, prostasin mRNA expression was detected by reverse transcription and real-time polymerase chain reaction in the bladder, and the prostasin protein was localized by immunohistochemistry in the urothelial cells. In mice injected intraperitoneally with bacterial lipopolysaccharide (LPS), bladder prostasin mRNA expression was downregulated, whereas the expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), interferon-gamma (IFN-gamma), TNF-alpha, IL-1beta, and IL-6 was upregulated. Viral promoter-driven expression of the human prostasin homolog in the bladder of transgenic mice attenuated the LPS induction of iNOS but did not abolish the induction. LPS induction of COX-2, TNF-alpha, IL-1beta, and IL-6 expression, however, was not reduced by prostasin transgene expression. Liposome-mediated delivery of prostasin-expressing plasmid into mouse bladder produced similar attenuation effects on LPS-induced iNOS expression, while not affecting COX-2 or cytokine induction. Mice receiving plasmid expressing a catalytic mutant prostasin did not manifest the iNOS induction attenuation phenotype. We propose a proteolytic mechanism for prostasin to intercept cytokine signaling during LPS-induced bladder inflammation.

Escherichia coli, fimbriae, bacterial persistence and host response induction in the human urinary tract

Urinary tract infections (UTI) are among the most common bacterial infections in humans. Symptomatic UTIs may be acute, recurrent or chronic but the most frequent form of UTI is asymptomatic bacteruria (ABU). In ABU, the mucosa remains inert, despite the presence of large bacterial numbers in urine. The difference in disease severity reflects the virulence of the infecting strain and the propensity of the host to respond to infection. It is essential to understand the molecular basis of disease diversity and the molecular interactions between bacteria and host that determine asymptomatic carriage and the transition to disease. We discuss the initial interactions between bacteria and the mucosal surfaces in the human urinary tract, and the bacterial factors involved in the breach of mucosal inertia. Specifically, the contribution of P and type 1 fimbriae to bacterial establishment and host response induction are investigated. The results show that P fimbriae serve as independent virulence factors when expressed by an ABU strain, by promoting the establishment of bacteriuria and the innate host response, which is the cause of symptoms and tissue damage. P fimbriae thus fulfil the molecular Koch postulates as independent virulence factors in the human urinary tract. Type 1 fimbriae, in contrast, did not act as virulence factors in this model, and thus appear to serve a different function in man than in the murine model.

Pyelonephritic Escherichia coli expressing P fimbriae decrease immune response of the mouse kidney

P fimbriae are proteinaceous appendages on the surface of Escherichia coli bacteria that mediate adherence to uroepithelial cells. E. coli that express P fimbriae account for the majority of ascending urinary tract infections in women with normal urinary tracts. The hypothesis that P fimbriae on uropathic E. coli attach to renal epithelia and may regulate the immune response to establish infection was investigated. The polymeric Ig receptor (pIgR), produced by renal epithelia, transports IgA into the urinary space. Kidney pIgR and urine IgA levels were analyzed in a mouse model of ascending pyelonephritis, using E. coli with (P+) and without (P-) P fimbriae, to determine whether P(+) E. coli regulate epithelial pIgR expression and IgA transport into the urine. (P+) E. coli establish infection and persist to a greater amount than P(-) E. coli. P(+)-infected mice downregulate pIgR mRNA and protein levels compared with P(-)-infected or PBS controls at > or =48 h. The decrease in pIgR was associated with decreased urinary IgA levels in the P(+)-infected group at 48 h. pIgR mRNA and protein also decline in P(+) E. coli-infected LPS-hyporesponsive mice. These studies identify a novel virulence mechanism of E. coli that express P fimbriae. It is proposed that P fimbriae decrease pIgR expression in the kidney and consequently decrease IgA transport into the urinary space. This may explain, in part, how E. coli that bear P fimbriae exploit the immune system of human hosts to establish ascending pyelonephritis.

Chemokine response to febrile urinary tract infection

BACKGROUND

Mucosal CXC chemokines recruit inflammatory cells to the infected urinary tract. The chemokine response repertoire of the urinary tract and the relationship to disease severity have not been examined, however.

METHODS

This study quantified CXC (CXCL1, CXCL3, CXCL5, CXCL8, CXCL9, and CXCL10) and CC (CCL2, CCL4, and CCL5) chemokines in sequential urine samples obtained from 50 patients with febrile urinary tract infections during 24 hours after diagnosis.

RESULTS

All patients had elevated chemokine levels, but bacteremic infections caused higher CXCL1, CXCL3, CXCL5, CXCL8, and CCL2 responses. CCL2 and CXCL8 levels were higher in patients with acute pyelonephritis symptoms and CCL2, CXCL3, CCL4, CXCL5, and CXCL10 were significantly correlated to C-reactive protein (CRP) and temperature. Women and men showed different chemokine responses.

CONCLUSION

Febrile urinary tract infections are accompanied by a complex chemokine response. The response magnitude reflects disease severity, and the repertoire is influenced by gender and underlying disease.

The liquidlike ordering of lipid A-diphosphate colloidal crystals: The influence of Ca2+, Mg2+, Na+, and K+ on the ordering of colloidal suspensions of lipid A-diphosphate in aqueous solutions

A comprehensive study was performed on electrostatically stabilized aqueous dispersion of lipid A-diphosphate in the presence of bound Ca2+, Mg2+, K+, and Na+ ions at low ionic strength (0.10-10.0-mM NaCl, 25 degrees C) over a range of volume fraction of 1.0 x 10(-4)< or =phi< or =4.95 x 10(-4). These suspensions were characterized by light scattering (LS), quasielastic light scattering, small-angle x-ray scattering, transmission electron microscopy, scanning electron microscopy, conductivity measurements, and acid-base titrations. LS and electron microscopy yielded similar values for particle sizes, particle size distributions, and polydispersity. The measured static structure factor, S(Q), of lipid A-diphosphate was seen to be heavily dependent on the nature and concentration of the counterions, e.g., Ca2+ at 5.0 nM, Mg2+ at 15.0 microM, and K+ at 100.0 microM (25 degrees C). The magnitude and position of the S(Q) peaks depend not only on the divalent ion concentration (Ca2+ and Mg2+) but also on the order of addition of the counterions to the lipid A-diphosphate suspension in the presence of 0.1-microM NaCl. Significant changes in the rms radii of gyration (R2G) 1/2 of the lipid A-diphosphate particles were observed in the presence of Ca2+ (24.8+/-0.8 nm), Mg2+ (28.5+/-0.7 nm), and K+ (25.2+/-0.6 nm), whereas the Na+ salt (29.1+/-0.8 nm) has a value similar to the one found for the de-ionized lipid A-diphosphate suspensions (29.2+/-0.8 nm). Effective particle charges were determined by fits of the integral equation calculations of the polydisperse static structure factor, S(Q), to the light-scattering data and they were found to be in the range of Z*=700-750 for the lipid A-diphosphate salts under investigation. The light-scattering data indicated that only a small fraction of the ionizable surface sites (phosphate) of the lipid A-diphosphate was partly dissociated (approximately 30%). It was also discovered that a given amount of Ca2+ (1.0-5.0 nM) or K+ (100 microM) influenced the structure much more than Na+ (0.1-10.0-mM NaCl) or Mg2+ (50 microM). By comparing the heights and positions of the structure factor peaks S(Q) for lipid A-diphosphate-Na+ and lipid A-diphosphate-Ca2+, it was concluded that the structure factor does not depend simply on ionic strength but more importantly on the internal structural arrangements of the lipid A-diphosphate assembly in the presence of the bound cations. The liquidlike interactions revealed a considerable degree of ordering in solution accounting for the primary S(Q) peak and also the secondary minimum at large particle separation. The ordering of lipid A-diphosphate-Ca2+ colloidal crystals in suspension showed six to seven discrete diffraction peaks and revealed a face-centered-cubic (fcc) lattice type (a=56.3 nm) at a volume fraction of 3.2 x 10(-4)< or =phi< or =3.9 x 10(-4). The K+ salt also exhibited a fcc lattice (a=55.92 nm) at the same volume fractions, but reveals a different peak intensity distribution, as seen for the lipid A-diphosphate-Ca2+ salt. However, the Mg2+ and the Na+ salts of lipid A-diphosphate showed body-centered-cubic (bcc) lattices with a=45.50 nm and a=41.50 nm, respectively (3.2 x 10(-4)< or =phi< or =3.9 x 10(-4)), displaying the same intensity distribution with the exception of the (220) diffraction peaks, which differ in intensity for both salts of lipid A-diphosphate.

THE INFLUENCE OF UROPATHOGENIC ESCHERICHIA COLI AND PROINFLAMMATORY CYTOKINES ON THE INDUCIBLE NITRIC OXIDE SYNTHASE RESPONSE IN HUMAN KIDNEY EPITHELIAL CELLS

PURPOSE

Nitric oxide (NO) is an antibacterial factor that is produced by the enzyme inducible NO synthase (iNOS). Uroepithelial cells express iNOS in experimental models of urinary tract infection but the stimulatory and regulatory mechanisms are still unclear. We investigated the influence of uropathogenic Escherichia coli strains with different fimbrial expression and the effect of proinflammatory cytokines on the host iNOS response.

MATERIALS AND METHODS

A498 human kidney epithelial cells were stimulated with different uropathogenic E. coli strains, namely the P and type 1-fimbriated clinical isolate AD110, the recombinant P-fimbriated strain E. coli HB101(pPIL110-75) and the recombinant type 1-fimbriated strain E. coli AAEC191A(pPKL4). NO production was determined as nitrite production in cell culture medium. Studies of nuclear factor-kappaB (NF-kappaB) binding to the iNOS promoter and reverse transcriptase-polymerase chain reaction of iNOS mRNA were performed to investigate iNOS gene activation in response to uropathogenic E. coli. The effect of interleukin (IL)-6, IL-8 and transforming growth factor-beta on NO production was also examined.

RESULTS

E. coli per se failed to induce NO production and iNOS mRNA in A498 cells. However, in combination with interferon-gamma AD110 and the type 1-fimbriated strain caused a small increase in NO production and iNOS mRNA. AD110 stimulated A498 cells demonstrated weak binding of NF-kappaB to a human iNOS promoter sequence. IL-6, IL-8 and transforming growth factor-a did not affect NO production in A498 cells.

CONCLUSIONS

Uropathogenic bacteria are weak inducers of human uroepithelial iNOS, which may be related to insufficient binding of NF-kappaB to iNOS promoter. The uroepithelial iNOS response did not appear to be regulated by proinflammatory cytokines.

Minireview: functions of the renal tract epithelium in coordinating the innate immune response to infection

Infection of the urinary tract remains one of the most common infections affecting mankind. Renal epithelial cells, being one of the first cells to come into contact with invading organisms, are in a key position to coordinate host defense. The epithelium not only provides a physical barrier to infection, but can also augment the immune response via the production of a number of inflammatory mediators and antimicrobial proteins. Recent work has demonstrated that cells of the innate immune system, including epithelial cells, express toll-like receptors (TLRs), with the capacity to recognize bacterial components. Although the exact mechanisms remain unclear, engagement of TLRs can lead to epithelial cell activation and the production of inflammatory mediators. These include complement proteins, other bactericidal peptides, and chemotactic cytokines. The resulting inflammatory infiltrate serves to aid bacterial clearance, but can also lead to renal damage. In this review, we describe how renal epithelial cells contribute to the innate immune response to ascending urinary tract infection. We specifically relate previous work to more recent developments in this field. An improved understanding of the mechanisms involved may highlight potential therapeutic avenues to aid bacterial clearance and prevent the renal scarring associated with infection.

Structure-activity relationships of galabioside derivatives as inhibitors of E. coli and S. suis adhesins: nanomolar inhibitors of S. suis adhesins

Four collections of Gal alpha1-4Gal derivatives were synthesised and evaluated as inhibitors of the PapG class II adhesin of uropathogenic Escherichia coli and of the P(N) and P(O) adhesins of Streptococcus suis strains. Galabiosides carrying aromatic structures at C1, methoxyphenyl O-galabiosides in particular, were identified as potent inhibitors of the PapG adhesin. Phenylurea derivatisation at C3' and methoxymethylation at O2' of galabiose provided inhibitors of the S. suis strains type P(N) adhesin with remarkably high affinities (30 and 50 nM, respectively). In addition, quantitative structure-activity relationship models for E. coli PapG adhesin and S. suis adhesin type P(O) were developed using multivariate data analysis. The inhibitory lead structures constitute an advancement towards high-affinity inhibitors as potential anti-adhesion therapeutic agents targeting bacterial infections.

Toll-like receptor 4 expression and cytokine responses in the human urinary tract mucosa

Mucosal pathogens trigger a local innate host response by activating epithelial cells. Bacterial adherence and Toll-like receptor 4 (TLR4) signaling have been implicated as key events in this process. This study addressed the molecular basis of the epithelial response to gram-negative infection in the human urinary tract. Mucosal biopsies were obtained from kidneys, ureters, and bladders of patients undergoing urinary tract surgery, and epithelial TLR4 and CD14 expression was examined by immunohistochemistry. TLR4 was detected in epithelial cells lining the entire urinary tract and in the renal tubular epithelium. CD14, in contrast, was completely absent from the epithelial tissue. The response of the epithelial cells to infection was studied by in vitro challenge of the biopsies with uropathogenic Escherichia coli bacteria. A rapid cytokine response was observed, with production of interleukin-1beta (IL-1beta), IL-6, and IL-8 but not of IL-4 or gamma interferon. Adhering, P- or type 1-fimbriated E. coli activated IL-6 and IL-8 production more efficiently than the nonfimbriated control, as shown by cellular staining and analysis of secreted cytokines. The results demonstrate that human uroepithelial cells possess the molecular machinery needed to respond to uropathogenic E. coli. This includes recognition receptors for fimbriae and TLR4 for transmembrane signaling. We speculate that the lack of membrane-bound CD14 allows the epithelium to regulate its sensitivity to lipopolysaccharide and to discriminate between more-virulent and less-virulent strains.

A toll-like receptor that prevents infection by uropathogenic bacteria

Toll-like receptors (TLRs) recognize molecular patterns displayed by microorganisms, and their subsequent activation leads to the transcription of appropriate host-defense genes. Here we report the cloning and characterization of a member of the mammalian TLR family, TLR11, that displays a distinct pattern of expression in macrophages and liver, kidney, and bladder epithelial cells. Cells expressing TLR11 fail to respond to known TLR ligands but instead respond specifically to uropathogenic bacteria. Mice lacking TLR11 are highly susceptible to infection of the kidneys by uropathogenic bacteria, indicating a potentially important role for TLR11 in preventing infection of internal organs of the urogenital system.

An msbB homologue carried in plasmid pO157 encodes an acyltransferase involved in lipid A biosynthesis in Escherichia coli O157:H7

Escherichia coli O157:H7 carries a chromosomal msbB1 and a plasmid-encoded msbB2 gene. We characterized msbB2 function as a homologue of msbB1 by examination of wild-type organisms and mutant strains that lacked functional msbB1, msbB2, and both msbB1 and msbB2. The msbB double-mutant strain generated pentaacyl lipid A, while the single-mutant strains synthesized hexaacyl lipid A. Complementation with overexpressed msbB2 converted pentaacyl into hexaacyl lipid A in the double-mutant strain. The transcription of both msbB genes occurred simultaneously. Lack of MsbB2 activity slightly increased the microheterogeneity of the lipid A species. These results suggest that the msbB2 gene plays a role not only in the routine generation of fully hexaacylated lipid A but also in suppressing the microheterogeneity of lipid A species, the endotoxic determinant of the organism.

Structural requirements for TLR4-mediated LPS signalling: a biological role for LPS modifications

Cells of the mucosal lining are the first to encounter invading bacteria during infection, and as such, they have developed numerous ways of detecting microbial intruders. Recently, we showed that epithelial cells recognize lipopolysaccharide (LPS) through the CD14-Toll-like receptor (TLR)-4 complex. Here, we identify the substructures of LPS that are recognized by the TLR4 receptor complex. In contrast to lipid A, the O-antigen does not mediate an inflammatory response; rather it interferes with the lipid A recognition. An Escherichia coli strain genetically modified to express penta-acylated lipid A not only showed reduced immunogenicity, but was also found to inhibit pro-inflammatory signalling induced by wild-type E. coli (hexa-acylated lipid A) as well as LPS from other bacteria of the Enterobacteriaceae family. Furthermore, penta-acylated LPS from Pseudomonas aeruginosa acted as an antagonist to hexa-acylated E. coli LPS, as did E. coli, as shown by its inhibitory effect on IL-8 production in stimulated cells. Hypo-acylated lipid A, such as that of P. aeruginosa, is found in several species within the gut microflora as well as in several bacteria causing chronic infections. Thus, our results suggest that the composition of the microflora may be important in modulating pro-inflammatory signalling in epithelial cells under normal as well as pathologic conditions.

Activation of NF-kappaB and IL-8 by Yersinia enterocolitica invasin protein is conferred by engagement of Rac1 and MAP kinase cascades

Yersinia enterocolitica triggers activation of the nuclear factor (NF)-kappaB and production of the proinflammatory chemokine interleukin (IL)-8 in intestinal epithelial cells. This activation is due to adhesion of the bacteria via their outer membrane protein invasin to the host cells. Using Clostridium difficile toxins that specifically inactivate small GTPases, and transfection of inhibitory proteins of the Rho-GTPases, we demonstrate that Rac1, but not Cdc42 or Rho, is required for activation of NF-kappaB by invasin. Invasin activated the mitogen activated protein kinases (MAPK) p38 and c-Jun N-terminal protein kinase (JNK) but not extracellular signal regulated kinase (ERK). The functional relevance of these pathways for invasin-mediated IL-8 expression was assessed by protein kinase inhibitors and dominant-negative kinase mutants. While NF-kappaB and JNK contribute to IL-8 transcription, p38 MAPK also acts through stabilization of IL-8 mRNA, as confirmed by quantitative RT-PCR and electrophoretic mobility shift assays. Transfection experiments with I-kappaB kinase (IKK)1 and IKK2 mutants indicate that the release of NF-kappaB from its cytoplasmic inhibitor I-kappaB and its translocation into the nucleus is mediated by these kinases. Our data identify Rac1 as a key intermediate in invasin-triggered IL-8 synthesis and demonstrate that maximum IL-8 induction involves several MAP kinase cascades.

Toll-like receptor 4-mediated signaling by epithelial surfaces: necessity or threat?

Recent data suggest that the lipopolysaccharide receptor Toll-like receptor (TLR) 4 is expressed by epithelial cells and might play a role in the mucosal host defense against Gram-negative bacteria. However, since many body surfaces are colonized by the physiological microflora, activation of epithelial TLRs must be tightly controlled to avoid unintended stimulation and mucosal inflammation. The present review summarizes the current understanding of TLR4-mediated recognition and addresses specific questions on microbial recognition on mucosal surfaces, with particular emphasis on the gastrointestinal and urinary tract.

The Escherichia coli AIDA autotransporter adhesin recognizes an integral membrane glycoprotein as receptor

The AIDA-I autotransporter adhesin, as a prototype of the AIDA adhesin family, represents a tripartite antigen consisting of the functional adhesin AIDA-I (alpha-domain), which mediates the specific attachment of bacteria to target cells, and a two-domain translocator (AIDA(c)) organized in the beta(1)- and beta(2)-domains. Cellular receptor moieties for the adhesin AIDA-I have not been identified. Here, it is demonstrated that the purified adhesin binds specifically to a high-affinity class of receptors on HeLa cells. Additionally, the adhesin was found to bind to a variety of mammalian cell types, indicating a broad tissue distribution of the receptor moiety. By using complementary techniques, including co-immunoprecipitation and one- and two-dimensional gel electrophoresis, the AIDA-I binding protein on HeLa cells was identified as a surface glycoprotein of about 119 kDa (gp119). The gp119 AIDA-I cellular receptor protein was characterized biochemically and found to be an integral N-glycosylated membrane protein with a pI of 5.2.

Novel approaches to prevention of urinary tract infections

Urinary tract infections are common clinical entities occurring in a variety of patient groups, most frequently caused by uropathogenic E. coli. Novel methods of preventing UTI currently under development are focused on three key approaches: (1) use of cranberry products, (2) restoration of the normal flora using Lactobacillus-based probiotic preparations, and (3) vaccine development. Although promising studies in each of these areas have been published or are ongoing, additional properly designed and powered clinical studies based on solid scientific evidence are needed.

Erratum to “The role of P fimbriae for Escherichia coli establishment and mucosal inflammation in the human urinary tract”

Bacterial adhesion to the bladder mucosa is a critical step for the establishment of Escherichia coli bacteriuria. The P-fimbriae, encoded by the pap gene cluster, are considered as virulence factors but the mechanisms have been debated. This study defined the roles for P fimbriation during the early colonization of the human urinary tract. Patients with recurrent UTI were first subjected to deliberate colonization with the non-fimbriated ABU strain E. coli 83972. Bacteriuria was established long term (1-4 years) in patients with dysfunctional bladders, but not in the patients with normal bladder function. Super-infections were transient and asymptomatic. P fimbriated transformants of the ABU strain (E. coli 83972pap+/prs+) reached 105 CFU/ml more rapidly than E. coli 83972 and the vector control. This was demonstrated by group wise and intra-individual analysis in patients colonized on different occasions with E. coli 83972 or the P fimbriated transformants. Higher neutrophil numbers and IL-8 and IL-6 concentrations in urine were obtained after colonization with the P fimbriated transformants. These results demonstrated that transformation of E. coli 83972 with the pap sequences is sufficient to convert it to a more potent host response inducer. The P fimbriae were shown to lower the significant bacteriuria threshold. The P fimbriated transformants needed lower bacterial numbers (103-4 CFU/ml) to predict a positive second urine culture with a >80% accuracy and to trigger a significant host response. These studies show that P fimbriae fulfil the Koch Henles molecular postulates for bacterial establishment and host response induction in the human urinary tract.

The host response to urinary tract infection

The authors use the UTI model to identify basic mechanisms of disease pathogenesis, host response induction, and defense. Their studies hold the promise to provide a molecular and genetic explanation for susceptibility to UTI, and to offer more precise tools for diagnosis and therapy of these infections. There are few infections where the host response is understood in such detail and where pathologic host responses can be linked to distinct disease states. The susceptibility to UTI varies greatly in the population. The studies suggest that distinct molecular defects can cause the clinical entity of acute pyelonephritis with renal scarring, and suggest that the susceptibility to UTI in certain patient groups may have a genetic basis. In addition, the distinct signal transduction pathways explain the development of symptoms, and propose that defects in those signaling mechanisms may occur in patients with ABU. In the future, it may be useful to include these host response parameters in the diagnostic arsenal, to help in early detection of patients susceptible to recurrent UTI and renal scarring. These patients may then be offered therapies that strengthen their defense, and be offered close surveillance for recurrences and other complications.

Interleukin-10 and nerve growth factor have reciprocal upregulatory effects on intestinal epithelial cells

The intestinal mucosa is in a constant state of controlled inflammation, but the processes whereby this occurs are poorly understood. The aims of this study were to look at the role of IL-10 and nerve growth factor (NGF) in intestinal epithelial cell regulation. The human colon epithelial cell lines T84, HT-29, and CACO-2 were used. RT-PCR, flow cytometry analysis, and immunohistochemistry were applied to measure the cytokine changes in epithelial cells induced by recombinant cholera toxin and its B subunit, IL-10, and NGF. Cholera toxin B subunit caused selective dose-dependent increased mRNA for IL-10 in T84 cells and the protein in T84, HT-29, and CACO-2 cells. IL-10 dose dependently selectively increased NGF mRNA in T84 cells and intracellular protein synthesis in all three epithelial cell lines. The effect of NGF was reciprocal, selective, and dose dependent because it increased mRNA for IL-10 and IL-10 synthesis. Our results suggest that the epithelium may actively participate in downregulation through innate mechanisms involving IL-10 and NGF. The reciprocal interaction suggests for the first time that NGF may be involved in local downregulation by mucosal epithelium and thus may play a potent protective role in response to injury, by prevention of undue inflammation.

CD14- and Toll-like receptor-dependent activation of bladder epithelial cells by lipopolysaccharide and type 1 piliated Escherichia coli

The gram-negative bacterium Escherichia coli is the leading cause of urinary tract infection. The interaction between type 1 piliated E. coli and bladder epithelial cells leads to the rapid production of inflammatory mediators, such as interleukin-6 (IL-6) and IL-8. Conflicting reports have been published in the literature regarding the mechanism by which uroepithelial cells are activated by type 1 piliated E. coli. In particular, the role of lipopolysaccharide (LPS) in these responses has been an area of significant debate. Much of the data arguing against LPS-mediated activation of bladder epithelial cells have come from studies using a renal epithelial cell line as an in vitro model of the urinary epithelium. In this report, we analyzed three bladder epithelial cell lines and demonstrated that they all respond to LPS. Furthermore, the LPS responsivity of the cell lines directly correlated with their ability to generate IL-6 after E. coli stimulation. The LPS receptor complex utilized by the bladder epithelial cell lines included CD14 and Toll-like receptors, and signaling involved the activation of NF-kappaB and p38 mitogen-activated protein kinase. Also, reverse transcription-PCR analysis demonstrated that bladder epithelial cells express CD14 mRNA. Thus, the molecular machinery utilized by bladder epithelial cells for the recognition of E. coli is very similar to that described for traditional innate immune cells, such as macrophages. In contrast, the A498 renal epithelial cell line did not express CD14, was hyporesponsive to LPS stimulation, and demonstrated poor IL-6 responses to E. coli.

The innate and early immune response to pathogen challenge in the female genital tract and the pivotal role of epithelial cells

The female reproductive tract is immunologically unique in its requirement for tolerance to allogeneic sperm and, in the upper tract, to the conceptus. However, it must also be appropriately protected from, and respond to, a diverse array of sexually transmitted pathogens. Some of these infections can be lethal (e.g. Human Immunodeficiency Virus (HIV), Human Papilloma Virus (HPV)), and others (e.g. Chlamydia trachomatis and Neisseria gonorrhoeae) can have potentially devastating reproductive sequelae. Interactions between a host and a pathogen are complex, diverse and regulated, and are a function of the individual pathogen, and host immunity. Although there is undoubtedly commonality in the mucosal immune response, there is also evidence of a degree of site-specificity in immune mechanisms, dependent upon the function and anatomical location of an organ. In this article, we review the evidence on the pivotal role of epithelial cells in the innate and early immune response to pathogen challenge in female genital tract tissues, and examine the evidence that the 'sterile' upper and the 'non-sterile' lower female genital tract may maintain a different immunological surveillance milieu, and may also respond differentially to pathogen challenge. We also review the unique characteristics, and subsequent ramifications of the acute cervical immune response to C. trachomatis, and discuss how natural antimicrobial mediators of immunity may be utilized to decrease the spread of sexually transmitted infections.

Characterization of a novel intracellularly activated gene from Salmonella enterica serovar typhi

A Salmonella enterica serovar Typhi gene that is selectively up-regulated upon bacterial invasion of eukaryotic cells was characterized. The open reading frame encodes a 298-amino-acid hydrophobic polypeptide (30.8 kDa), which is predicted to be an integral membrane protein with nine membrane-spanning domains. The protein is closely related (87 to 94% reliability) to different transport and permease systems. Gene expression under laboratory conditions was relatively weak; however, sevenfold induction was observed in a high-osmolarity medium (300 mM NaCl). The growth pattern in a laboratory medium of a serovar Typhi strain Ty2 derivative containing a 735-bp in-frame deletion in this gene, named gaiA (for gene activated intracellularly), was not affected. In contrast, the mutant was partially impaired in intracellular survival in murine peritoneal macrophages, as well as in human monocyte-derived macrophages. However, in the case of human macrophages, this survival defect was modest and evident only at late infection times (24 h). Despite the distinct intracellular survival kinetics displayed in macrophages of different species, the gaiA null mutant was significantly affected in its potential to trigger apoptosis in both murine and human macrophages. Provision of the gaiA gene in trans resulted in complementation of these phenotypes. Interestingly, the absence of a functional gaiA gene caused a marked attenuation in the mouse mucin model, as shown by the increase (3 orders of magnitude) in the 50% lethal dose of the mutant strain over that of the parental strain Ty2 (P Collapse

Key Words Collapse

MESH Headings

• Amino Acid Sequence
• Animals
• Apoptosis
• Bacterial Proteins/genetics
• Bacterial Proteins/physiology
• Base Sequence
• DNA, Bacterial/genetics
• Gene Expression Regulation, Bacterial
• Genes, Bacterial
• Humans
• Macrophages/microbiology
• Macrophages/pathology
• Membrane Proteins/genetics
• Membrane Proteins/physiology
• Mice
• Molecular Sequence Data
• Mutation
• Salmonella Infections/etiology
• Salmonella Infections/microbiology
• Salmonella Infections/pathology
• Salmonella typhi/genetics
• Salmonella typhi/pathogenicity
• Virulence/genetics
• Virulence/physiology

Collapse

Grants Collapse

Affiliation(s)

Holger Basso Division of Microbiology, GBF-German Research Centre for Biotechnology, D-38124 Braunschweig, Germany
Faiza Rharbaoui
Lothar H Staendner
Eva Medina
Francisco García-Del Portillo
Carlos A Guzmán

Collapse