Role of EspA and intimin in expression of proinflammatory cytokines from enterocytes and lymphocytes by rabbit enteropathogenic Escherichia coli-infected rabbits

Compound Probiotics Improve Body Growth Performance by Enhancing Intestinal Development of Broilers with Subclinical Necrotic Enteritis

The aim of this study is to explore whether or not the combined application of BS15 and H2 is capable to have a more effective control effect on SNE in broilers. A total of 240 1-day-old female chickens were randomly divided into 5 groups: (a) basal diet in negative control group (NC group); (b) basal diet + SNE infection (coccidiosis vaccine + CP) (PC group); (c) basal diet + SNE infection + H2 pre-treatment (BT group); (d) basal diet + SNE infection + BS15 pre-treatment (LT group); and (e) basal diet + SNE infection + H2 pre-treatment + BS15 pre-treatment (MT group). The results showed the MT group had the most positive effect on inhibiting the negative effect of growth performance at 42 days of age. In the detection of the NC, PC, and MT group indicators at 28 days of age, we found that MT group significantly promoted ileum tissue development of broilers, and the ileum of broilers in the MT group formed a flora structure different from NC and PC, although it was found that the MT group had no effect on the butyrate level in the cecum, but it could affect the serum immune level, such as significantly reducing the level of pro-inflammatory cytokine IL-8 and increasing the content of immunoglobulin IgM and IgG. In conclusion, the composite preparation of Lactobacillus johnsonii BS15 and Bacillus licheniformis H2 could effectively improve the growth performance against SNE broilers, which is possibly caused by the improvement of the immune levels, the reduction of inflammation levels, and the promotion of the intestinal development.

Intestinal Barrier and Behavior

The intestinal barrier function contributes to gut homeostasis by modulating absorption of water, electrolytes, and nutrients from the lumen into the circulation while restricting the passage of noxious luminal substances and microorganisms. Chronic conditions such as rheumatoid arthritis, inflammatory bowel disease, and celiac disease are associated to intestinal barrier dysfunction. Here, the hypothesis is that a leaky intestinal wall allowing for indiscriminate passage of intraluminal compounds to the vascular compartment could in turn lead to systemic inflammation. An increasing number of studies are now investigating the association between gut permeability and CNS disorders, under the premise that translocation of intestinal luminal contents could affect CNS function, either directly or indirectly. Still, it is unknown whether disruption of intestinal barrier is a causative agent or a consequence in these situations. Here, we discuss the latest evidence pointing to an association between increased gut permeability and disrupted behavioral responses.

Role of virulence factors on host inflammatory response induced by diarrheagenic Escherichia coli pathotypes

ABSTRACT 

Pathogens are able to breach the intestinal barrier, and different bacterial species can display different abilities to colonize hosts and induce inflammation. Inflammatory response studies induced by enteropathogens as Escherichia coli are interesting since it has acquired diverse genetic mobile elements, leading to different E. coli pathotypes. Diarrheagenic E. coli secrete toxins, effectors and virulence factors that exploit the host cell functions to facilitate the bacterial colonization. Many bacterial proteins are delivered to the host cell for subverting the inflammatory response. Hereby, we have highlighted the specific processes used by E. coli pathotypes, by that subvert the inflammatory pathways. These mechanisms include an arrangement of pro- and anti-inflammatory responses to favor the appropriate environmental niche for the bacterial survival and growth.

The Inflammatory Response during Enterohemorrhagic Escherichia coli Infection

The inflammatory response is an integral part of host defense against enterohemorrhagic Escherichia coli (EHEC) infection and also contributes to disease pathology. In this article we explore the factors leading to inflammation during EHEC infection and the mechanisms EHEC and other attaching and effacing (A/E) pathogens have evolved to suppress inflammatory signaling. EHEC stimulates an inflammatory response in the intestine through host recognition of bacterial components such as flagellin and lipopolysaccharide. In addition, the activity of Shiga toxin and some type III secretion system effectors leads to increased tissue inflammation. Various infection models of EHEC and other A/E pathogens have revealed many of the immune factors that mediate this response. In particular, the outcome of infection is greatly influenced by the ability of an infected epithelial cell to mount an effective host inflammatory response. The inflammatory response of infected enterocytes is counterbalanced by the activity of type III secretion system effectors such as NleE and NleC that modify and inhibit components of the signaling pathways that lead to proinflammatory cytokine production. Overall, A/E pathogens have taught us that innate mucosal immune responses in the gastrointestinal tract during infection with A/E pathogens are highly complex and ultimate clearance of the pathogen depends on multiple factors, including inflammatory mediators, bacterial burden, and the function and integrity of resident intestinal epithelial cells.

Control of bacterial virulence by the RalR regulator of the rabbit-specific enteropathogenic Escherichia coli strain E22

Atypical enteropathogenic Escherichia coli (aEPEC) causes endemic diarrhea, diarrheal outbreaks, and persistent diarrhea in humans, but the mechanism by which aEPEC causes disease is incompletely understood. Virulence regulators and their associated regulons, which often include adhesins, play key roles in the expression of virulence factors in enteric pathogenic bacteria. In this study we identified a transcriptional regulator, RalR, in the rabbit-specific aEPEC strain, E22 (O103:H2) and examined its involvement in the regulation of virulence. Microarray analysis and quantitative real-time reverse transcription-PCR demonstrated that RalR enhances the expression of a number of genes encoding virulence-associated factors, including the Ral fimbria, the Aap dispersin, and its associated transport system, and downregulates several housekeeping genes, including fliC. These observations were confirmed by proteomic analysis of secreted and heat-extracted surface-associated proteins and by adherence and motility assays. To investigate the mechanism of RalR-mediated activation, we focused on its most highly upregulated target operons, ralCDEFGHI and aap. By using primer extension, electrophoretic mobility shift assay, and mutational analysis, we identified the promoter and operator sequences for these two operons. By employing promoter-lacZ reporter systems, we demonstrated that RalR activates the expression of its target genes by binding to one or more 8-bp palindromic sequences (with the consensus of TGTGCACA) located immediately upstream of the promoter core regions. Importantly, we also demonstrated that RalR is essential for virulence since infection of rabbits with E22 carrying a knockout mutation in the ralR gene completely abolished its ability to cause disease.

Nuclear factor κB is a key transcription factor in the duodenal contractility alterations induced by lipopolysaccharide

Alterations in intestinal motility are one of the features of sepsis induced by lipopolysaccharide (LPS). This study investigated the role of the nuclear transcription factor κB (NF-κB) in the LPS-induced duodenal contractility alterations, generation of reactive oxygen species (ROS) and production of cytokines in rabbit duodenum. Rabbits were treated with saline, LPS, sulfasalazine + LPS, pyrrolidinedithiocarbamate (PDTC) + LPS or RO 106-9920 + LPS. Contractility studies were performed in an organ bath. The formation of products of oxidative damage to proteins (carbonyls) and lipids (malondialdehyde and 4-hydroxyalkenals) was quantified in intestinal tissue and plasma. The protein expression of NF-κB was measured by Western blot. The DNA binding activity of NF-κB was evaluated by transcription factor activity assay. The expression of interleukin-1β, tumour necrosis factor α (TNF-α), interleukin-6, interleukin-10 and interleukin-8 mRNA was determined by RT-PCR. Sulfasalazine, PDTC and RO 106-9920 blocked the inhibitory effect of LPS on contractions induced by ACh in the longitudinal smooth muscle of rabbit duodenum. Sulfasalazine, PDTC and RO 106-9920 reduced the increased levels of malondialdehyde and 4-hydroxyalkenals and the carbonyls induced by LPS in plasma. Lipopolysaccharide induced the activation, translocation to the nucleus and DNA binding of NF-κB. Lipopolysaccharide increased the mRNA expression of interleukin-6 and TNF-α in duodenal tissue, and this effect was partly reversed by PDTC, sulfasalazine and RO 106-9920. In conclusion, NF-κB mediates duodenal contractility disturbances, the generation of ROS and the increase in the expression of interleukin-6 and TNF-α induced by LPS. Sulfasalazine, PDTC and RO 106-9920 may be therapeutic drugs to reduce these effects.

Intimate adherence by enteropathogenic Escherichia coli modulates TLR5 localization and proinflammatory host response in intestinal epithelial cells

Enteropathogenic Escherichia coli (EPEC) causes diarrhoeal disease by altering enterocyte physiology and producing mucosal inflammation. Many details concerning the host response against EPEC remain unknown. We evaluated the role of EPEC virulence factors on the inflammatory response through an analysis of bacterial recognition, cell signalling, and cytokine production using an in vitro epithelial cell infection model. Interestingly, we found that EPEC infection recruits Toll-like receptor 5 (TLR5) to the cell surface. We confirmed that type 3 secretion system (T3SS) and flagellin (FliC) are necessary for efficient extracellular regulated kinases 1 and 2 (ERK1/2) activation and found that intimin could down-regulate this pathway. Besides flagellin, intimin was required to keep nuclear factor kappa B (NF-κB) activated during infection. EPEC infection activated tumour necrosis factor alpha (TNF-α) production and induced interleukin (IL)-1β and IL-8 release. Virulence factors such as intimin, T3SS, EspA and fliC were required for IL-1β secretion, whereas intimin and T3SS participated in IL-8 release. Flagellin was essential for late secretion of TNF-α and IL-8 and intimin stimulated cytokine secretion. Initial adherence limited TNF-α release, whereas late attachment sustained TNF-α secretion. We conclude that intimin modulates TLR5 activation and intimate adherence alters the proinflammatory response.

Always one step ahead: How pathogenic bacteria use the type III secretion system to manipulate the intestinal mucosal immune system

The intestinal immune system and the epithelium are the first line of defense in the gut. Constantly exposed to microorganisms from the environment, the gut has complex defense mechanisms to prevent infections, as well as regulatory pathways to tolerate commensal bacteria and food antigens. Intestinal pathogens have developed strategies to regulate intestinal immunity and inflammation in order to establish or prolong infection. The organisms that employ a type III secretion system use a molecular syringe to deliver effector proteins into the cytoplasm of host cells. These effectors target the host cell cytoskeleton, cell organelles and signaling pathways. This review addresses the multiple mechanisms by which the type III secretion system targets the intestinal immune response, with a special focus on pathogenic E. coli.

The Streptococcus pneumoniae capsule is required for full virulence in pneumococcal endophthalmitis

PURPOSE

To determine whether Streptococcus pneumoniae capsule was necessary for pathogenesis of pneumococcal endophthalmitis.

METHODS

An isogenic capsule-deficient strain was created using homologous recombination. New Zealand White rabbits were injected intravitreously with 10(2) colony-forming units (CFU) of the parent strain or the capsule mutant. Slit lamp examination (SLE), electroretinography, and myeloperoxidase activity were performed 24 and 48 hours postinfection (PI). Serial dilutions of vitreous were plated to quantitate CFU, eyes were extracted for histology, and host cytokine mRNA expression was determined.

RESULTS

Eyes infected with the parent strain had significantly higher SLE scores than eyes infected with the capsule-deficient strain 24 and 48 hours PI (P < 0.001). CFU recovered from eyes infected with the capsule mutant were significantly fewer than CFU recovered from eyes infected with the parent strain 24 and 48 hours PI (P < 0.001). The parent strain caused a significantly greater decrease in retinal function and more retinal destruction than the mutant strain 48 hours PI (P = 0.026). Vitreal IL-1β, IL-6, and TNF-α were upregulated by both the parent and mutant strain 12 hours PI. By 48 hours PI, there was significantly more neutrophil infiltration in the vitreous infected with the parent strain.

CONCLUSIONS

Endophthalmitis caused by the encapsulated strain is more damaging to retinal function and structural integrity. These findings indicate that capsule is an important virulence factor of S. pneumoniae endophthalmitis, in contrast to keratitis, suggesting that the anatomic host site in pneumococcal ocular infections is important.

Inhibition of NF-κB signaling in human dendritic cells by the enteropathogenic Escherichia coli effector protein NleE

Intestinal dendritic cells (DCs) send processes between epithelial cells into the gut lumen to sample pathogens. Noninvasive enteropathogenic Escherichia coli (EPEC) colonize the gut using a type three secretion system (T3SS) to inject effector proteins into epithelial cells. We hypothesized that EPEC might also inject proteins into DC processes to dampen immune recognition. Using a T3SS-linked fluorescence resonance energy transfer-based system we show that EPEC injects effectors into in vitro grown human myeloid DCs. Injected cells emit a blue signal due to cleavage of the green fluorescence resonance energy transfer-based substrate CCF2/AM by β-lactamase. When cultured with a mutant EPEC unable to translocate effector proteins, myeloid DCs show rapid activation of NF-κB, secrete large amounts of proinflammatory cytokines and increase expression of CD80, CD83, and CD86, whereas wild-type EPEC barely elicits cytokine production and shuts off nuclear translocation of NF-κB p65. By deleting effector protein genes, we identified NleE as being critical for this effect. Expression of NleE in HeLa cells completely prevented nuclear p65 accumulation in response to IL1-β, and luciferase production in an NF-κB reporter cell line. DCs cocultured with wild-type EPEC or NleE-complemented strains were less potent at inducing MLR. EPEC was also able to inject effectors into DCs sending processes through model gut epithelium in a transwell system and into Peyer's patch myeloid DCs. Thus, EPEC translocate effectors into human DCs to dampen the inflammatory response elicited by its own pathogen-associated molecular patterns.

Pic, an autotransporter protein secreted by different pathogens in the Enterobacteriaceae family, is a potent mucus secretagogue

A hallmark of enteroaggregative Escherichia coli (EAEC) infection is a formation of biofilm, which comprises a mucus layer with immersed bacteria in the intestines of patients. While studying the mucinolytic activity of Pic in an in vivo system, rat ileal loops, we surprisingly found that EAEC induced hypersecretion of mucus, which was accompanied by an increase in the number of mucus-containing goblet cells. Interestingly, an isogenic pic mutant (EAEC Δpic) was unable to cause this mucus hypersecretion. Furthermore, purified Pic was also able to induce intestinal mucus hypersecretion, and this effect was abolished when Pic was heat denatured. Site-directed mutagenesis of the serine protease catalytic residue of Pic showed that, unlike the mucinolytic activity, secretagogue activity did not depend on this catalytic serine protease motif. Other pathogens harboring the pic gene, such as Shigella flexneri and uropathogenic E. coli (UPEC), also showed results similar to those for EAEC, and construction of isogenic pic mutants of S. flexneri and UPEC confirmed this secretagogue activity. Thus, Pic mucinase is responsible for one of the pathophysiologic features of the diarrhea mediated by EAEC and the mucoid diarrhea induced by S. flexneri.

Simultaneous inactivation of espB and tir abrogates the strong, but non-protective, inflammatory response induced by EPEC

Enteropathogenic Escherichia coli (EPEC) belong to the attaching and effacing (A/E) family of bacterial pathogens that represent a worldwide health concern. These non-invasive bacteria attach to intestinal enterocytes through a type III secretion system (T3SS), leading to intestinal inflammation and severe diarrhea. To dissect the signals leading to the induction of the inflammatory response and to understand its role in the pathogenesis of infection, we used the rabbit model, which represents a close model of human infections. Rabbits were orally inoculated with either the wild type O103:K-:H2 E22 EPEC strain or with the E22Δtir/espB strain, which bears mutations in two genes involved in the injectisome structure and function. To monitor the development of the inflammatory response, we developed a quantitative real-time RT-PCR (qPCR) assay specific for a panel of rabbit genes. Using combined immunohistochemistry and qPCR, we show here that the inflammatory response triggered by wild type EPEC occurs very early, preceding the bacterial colonization of the epithelium. However, this early response is unable to prevent bacterial attachment on enterocytes. Moreover, our results show that expression of a complete bacterial injectisome is required for the development of inflammation. Finally, infection by the virulent strain, but not by the doubly mutated strain, rapidly induces the development of a specific immune response in the mesenteric lymph nodes, which is not associated with protection. Our findings suggest that the induction of a strong inflammatory response by T3SS dependent components represents a selective advantage for T3SS+ bacteria, thereby facilitating their colonization.

Associations between mucosal innate and adaptive immune responses and resolution of diarrheal pathogen infections

The identification of immune response mechanisms that contribute to the control of diarrheal disease in developing countries remains an important priority. We addressed the role of fecal chemokines and cytokines in the resolution of diarrheal Escherichia coli and Giardia lamblia infections. Stools collected from 127 Mexican children 5 to 15 months of age enrolled in a randomized, double-blind, placebo-controlled, vitamin A supplementation trial were screened for enteropathogenic Escherichia coli (EPEC), enterotoxigenic E. coli (ETEC), and Giardia lamblia. Fecal concentrations of tumor necrosis factor alpha (TNF-alpha), monocyte chemoattractant protein-1 (MCP-1), interleukin-4 (IL-4), IL-5, IL-6, IL-8, IL-10, and interferon-gamma (IFN-gamma) were determined. Hazard models incorporating cytokine variables were fit to durations of asymptomatic and symptomatic pathogen infections, controlling for treatment group. Increased levels of TNF-alpha and IL-6 were associated with decreased durations of EPEC infection and increased ETEC durations. Increased IL-4 and IFN-gamma levels were associated with decreased and increased durations, respectively, of both EPEC and ETEC infections. Increased IL-10 levels were associated with increased and decreased durations of asymptomatic and symptomatic EPEC infections, respectively, and increased durations of both asymptomatic and symptomatic ETEC infections. Increased levels of MCP-1, IFN-gamma, IL-4, and IL-5 were associated with increased G. lamblia infection duration, while increased IL-8 levels were associated with decreased durations. Differences in proinflammatory and Treg cytokine levels are associated with differences in the resolution of inflammatory and noninflammatory pathogen infections.

The excretion of F18+ E. coli is reduced after oral immunisation of pigs with a FedF and F4 fimbriae conjugate

Currently, no vaccines are available for edema disease and post-weaning diarrhoea (PWD) in pigs. In the present study, a subunit vaccine containing the F18 fimbrial adhesin FedF was studied. Hereto, recombinant FedF was produced as a fusion protein with maltose-binding protein. Even though the produced MBPFedF was shown to attach in vitro to enterocytes, almost no FedF-specific immune response could be detected after oral administration to piglets. The delivery of FedF to the intestinal mucosa was improved by conjugating the MBPFedF to F4 fimbriae. Indeed, this conjugation induced a systemic and local FedF-specific immune response and led to a reduction in excretion after infection with F18+ E. coli. Although complete protection was not observed, the conjugation between FedF and F4 fimbriae can be considered as a first step towards the development of a combined vaccine against F4+ and F18+ E. coli infections.

Infection of rabbit kidney cells (RK13) by enteropathogenicEscherichia colias a model to study the dynamics of actin cytoskeleton

Enteropathogenic Escherichia coli (EPEC) colonizes the intestinal mucosa and causes a cell lesion known as attachment and effacement (A/E) lesion. The molecular mechanisms for A/E lesions include injection of Tir, which is a receptor for an adhesin named intimin. The Tir–intimin interaction causes rearrangement of the cytoskeleton forming actin-rich structures called pedestals. Unfortunately, the formation of the A/E lesions and the dynamics of the actin cytoskeleton during this rearrangement induced by EPEC cannot be studied in the natural host. However, there are EPEC strains that infect rabbit (REPEC) that are genetically and pathologically similar to EPEC. Here, we used REPEC for the infection of rabbit kidney epithelial cells, line RK13, as a model to understand the actin cytoskeleton dynamics during pedestal formation. Actin-rich pedestal formation during the infection of RK13 cells by REPEC was analyzed by electron and confocal microscopy. The kinetics of infection along with the use of antibiotics for eliminating the bacteria, as well as reinfection, evidenced the plasticity of the actin cytoskeleton during pedestal formation. Thus, this model is a helpful tool for studying the dynamics of actin cytoskeleton and for correlating the data with those observed in in vivo models in rabbits experimentally infected with REPEC.

Protective and destructive innate immune responses to enteropathogenic Escherichia coli and related A/E pathogens

Enteropathogenic Escherichia coli, enterohemorrhagic E. coli (O157:H7) and Citrobacter rodentium are classified as attaching and effacing (A/E) pathogens based on their ability to adhere to intestinal epithelium, destroy microvilli and induce pedestal formation at the site of infection. A/E bacterial infections also cause acute diarrheal episodes and intestinal inflammation. The use of model systems has led to an understanding of the innate immune response to A/E pathogens. The innate immune system plays a protective role, initiating a productive antibody response, directly killing bacteria and inducing repair mechanisms following tissue damage caused by infection. However, hyperactivation of the innate immune system can have negative consequences, including exacerbated tissue destruction following neutrophil infiltration. Here we review how innate immune cell types, including neutrophils, macrophages and dendritic cells, orchestrate both protective and destructive responses. Such information is crucial for the development of therapeutics that can mitigate destructive inflammatory responses while accentuating those that are protective.

Flagellin-dependent and -independent inflammatory responses following infection by enteropathogenic Escherichia coli and Citrobacter rodentium

Enteropathogenic Escherichia coli (EPEC) and the murine pathogen Citrobacter rodentium belong to the attaching and effacing (A/E) family of bacterial pathogens. These noninvasive bacteria infect intestinal enterocytes using a type 3 secretion system (T3SS), leading to diarrheal disease and intestinal inflammation. While flagellin, the secreted product of the EPEC fliC gene, causes the release of interleukin 8 (IL-8) from epithelial cells, it is unclear whether A/E bacteria also trigger epithelial inflammatory responses that are FliC independent. The aims of this study were to characterize the FliC dependence or independence of epithelial inflammatory responses to direct infection by EPEC or C. rodentium. Following infection of Caco-2 intestinal epithelial cells by wild-type and DeltafliC EPEC, a rapid activation of several proinflammatory genes, including those encoding IL-8, monocyte chemoattractant protein 1, macrophage inflammatory protein 3alpha (MIP3alpha), and beta-defensin 2, occurred in a FliC-dependent manner. These responses were accompanied by mitogen-activated protein kinase activation, as well as the Toll-like receptor 5 (TLR5)-dependent activation of NF-kappaB. At later infection time points, a subset of these proinflammatory genes (IL-8 and MIP3alpha) was also induced in cells infected with DeltafliC EPEC. The nonmotile A/E pathogen C. rodentium also triggered similar innate responses through a TLR5-independent but partially NF-kappaB-dependent mechanism. Moreover, the EPEC FliC-independent responses were increased in the absence of the locus of enterocyte effacement-encoded T3SS, suggesting that translocated bacterial effectors suppress rather than cause the FliC-independent inflammatory response. Thus, we demonstrate that infection of intestinal epithelial cells by A/E pathogens can trigger an array of proinflammatory responses from epithelial cells through both FliC-dependent and -independent pathways, expanding our understanding of the innate epithelial response to infection by these pathogens.

The effect of vitamin A supplementation on the intestinal immune response in Mexican children is modified by pathogen infections and diarrhea

Vitamin A supplementation has consistently reduced infant mortality and the severity of pathogen-induced diarrhea. The mechanism by which vitamin A modulates the mucosal immune response to produce these effects remains poorly defined. To address this issue, stools collected during the summer months from 127 Mexican children 5-15 mo old enrolled in a larger, randomized, double-blind, placebo-controlled, vitamin A supplementation trial were screened for interleukin (IL)-4, IL-6, interferon-gamma (IFN-gamma), and gastrointestinal pathogens. Fecal cytokine values were categorized into 3 levels (undetectable, <median, > or =median). Multinomial regression models were used to determine the probability that vitamin A-supplemented children had higher categorical values of a cytokine than children in the placebo group. Differences in categorical values were also analyzed after stratification by gastrointestinal pathogen infections and diarrheal symptoms. Overall, fecal cytokine categorical levels did not differ between children randomized to the 2 arms. Vitamin A-supplemented children infected with enteropathogenic E. coli (EPEC) had reduced IL-4 and IFN-gamma levels [odds ratio (OR) = 0.3, 95% CI 0.13-0.67 and OR = 0.34, 95% CI 0.14-0.83, respectively] compared with children in the placebo group. Vitamin A-supplemented children had increased IL-4 levels when infected with A. lumbricoides (OR = 12.06, 95% CI 0.95-153.85). In contrast, IL-4 levels increased (OR = 2.14, 95% CI 0.94-4.87) and IFN-gamma levels decreased (OR = 0.51, 95% CI 0.26-0.99) among vitamin A-supplemented children with diarrhea compared with children in the placebo group. These findings suggest that the regulation of the mucosal immune response by vitamin A may depend on the type of enteric pathogen infecting the child and the presence of clinical symptoms.

Enteropathogenic E. coli disrupts tight junction barrier function and structure in vivo

Enteropathogenic Escherichia coli (EPEC) infection disrupts tight junctions (TJs) and perturbs intestinal barrier function in vitro. E. coli secreted protein F (EspF) is, in large part, responsible for these physiological and morphological alterations. We recently reported that the C57BL/6J mouse is a valid in vivo model of EPEC infection as EPEC colonizes the intestinal epithelium and effaces microvilli. Our current aim was to examine the effects of EPEC on TJ structure and barrier function of the mouse intestine and to determine the role of EspF in vivo. C57BL/6J mice were gavaged with approximately 2 x 10(8) EPEC organisms or PBS. At 1 or 5 days postinfection, mice were killed and ileal and colonic tissue was mounted in Ussing chambers to determine barrier function (measured as transepithelial resistance) and short circuit current. TJ structure was analyzed by immunofluorescence microscopy. Wild-type (WT) EPEC significantly diminished the barrier function of ileal and colonic mucosa at 1 and 5 days postinfection. Deficits in barrier function correlated with redistribution of occludin in both tissues. Infection with an EPEC strain deficient of EspF (delta espF) had no effect on barrier function at 1 day postinfection. Furthermore, delta espF had no effect on ileal TJ morphology and minor alterations of colonic TJ morphology at 1 day postinfection. In contrast, at 5 days postinfection, WT EPEC and delta espF had similar effects on barrier function and occludin localization. In both cases this was associated with immune activation, as demonstrated by increased mucosal tumor necrosis factor-alpha levels 5 days postinfection. In conclusion, these data demonstrate that WT EPEC infection of 6-8-week-old C57BL/6J mice (1) significantly decreases barrier function in the ileum and colon (2) redistributes occludin in the ileum and colon and (3) is dependent upon EspF to induce TJ barrier defects at early, but not late, times postinfection.

Host immune status influences the development of attaching and effacing lesions in weaned pigs

Attaching and effacing Escherichia coli (AEEC) has been associated with naturally occurring attaching and effacing (A/E) lesions in weaned pigs, and although A/E lesions have been experimentally reproduced in newborn piglets, such lesions have been much more difficult to induce in older conventional pigs. Hence, the aim of this study was to examine the effect of oral administration of dexamethasone on the development of A/E lesions in weaned pigs challenged with a porcine enteropathogenic E. coli (PEPEC) strain and to investigate the involvement of local intestinal cytokine response. Dexamethasone, given orally at a dosage of 3 mg kg of body weight(-1), significantly enhanced both the colonization of the challenge strain and the prevalence of foci of intimately adherent bacteria, resulting in extensive A/E lesions in the ileum, cecum, and colon of challenged pigs. We also confirmed the expression of both intimin and Tir by PEPEC strain ECL1001 in A/E lesions in vivo, which is, to our knowledge, the first report of the involvement of the latter proteins in any AEEC infections in vivo. Moreover, semiquantitative reverse transcription-PCR demonstrated that interleukin 1beta (IL-1beta), IL-6, IL-8, and, to a lesser extent, IL-12p40 are significantly upregulated in the ileum following challenge with strain ECL1001, whereas dexamethasone blocks such upregulation. Taken together, our results strongly suggested that host immune status influences the development of A/E lesions in weaned pigs, and it appears that IL-1beta, IL-6, IL-8, and, to a lesser extent, IL-12p40 are expressed during infection of weaned pigs by PEPEC and may contribute to the natural resistance of the host against PEPEC infection.