Invasive ability of an Escherichia coli strain isolated from the ileal mucosa of a patient with Crohn's disease

Crohn's disease-associated adherent-invasive Escherichia coli adhesion is enhanced by exposure to the ubiquitous dietary polysaccharide maltodextrin

Crohn's disease (CD) is associated with intestinal dysbiosis evidenced by an altered microbiome forming thick biofilms on the epithelium. Additionally, adherent-invasive E. coli (AIEC) strains are frequently isolated from ileal lesions of CD patients indicating a potential role for these strains in disease pathogenesis. The composition and characteristics of the host microbiome are influenced by environmental factors, particularly diet. Polysaccharides added to food as emulsifiers, stabilizers or bulking agents have been linked to bacteria-associated intestinal disorders. The escalating consumption of polysaccharides in Western diets parallels an increased incidence of CD during the latter 20^th century. In this study, the effect of a polysaccharide panel on adhesiveness of the CD-associated AIEC strain LF82 was analyzed to determine if these food additives promote disease-associated bacterial phenotypes. Maltodextrin (MDX), a polysaccharide derived from starch hydrolysis, markedly enhanced LF82 specific biofilm formation. Biofilm formation of multiple other E. coli strains was also promoted by MDX. MDX-induced E. coli biofilm formation was independent of polysaccharide chain length indicating a requirement for MDX metabolism. MDX exposure induced type I pili expression, which was required for MDX-enhanced biofilm formation. MDX also increased bacterial adhesion to human intestinal epithelial cell monolayers in a mechanism dependent on type 1 pili and independent of the cellular receptor CEACAM6, suggesting a novel mechanism of epithelial cell adhesion. Analysis of mucosa-associated bacteria from individuals with and without CD showed increased prevalence of malX, a gene essential for MDX metabolism, uniquely in the ileum of CD patients. These findings demonstrate that the ubiquitous dietary component MDX enhances E. coli adhesion and suggests a mechanism by which Western diets rich in specific polysaccharides may promote dysbiosis of gut microbes and contribute to disease susceptibility.

Adherent-invasive Escherichia coli blocks interferon-γ-induced signal transducer and activator of transcription (STAT)-1 in human intestinal epithelial cells

Adherent-invasive Escherichia coli (AIEC) is a pathogen isolated from the ileum of patients with Crohn disease. IFNγ is a key mediator of immunity, which regulates inflammatory responses to microbial infections. Previously, we showed enterohemorrhagic E. coli prevents STAT1 activation. The aim of this study was to determine whether activation of STAT1 by IFNγ was prevented by AIEC infection, and to define the mechanisms used. Human epithelial cells were infected with three different AIEC strains or other pathogenic and commensal E. coli strains. Following infection, cells were stimulated with IFNγ, and STAT1 activation was monitored by immunoblotting. Our data show that live AIEC with active protein synthesis machinery is able to prevent IFNγ-mediated STAT1 phosphorylation, and that a secreted factor may be involved. We conclude that the suppression of epithelial cell STAT1 signal transduction by AIEC strains isolated from patients with Crohn disease represents a novel mechanism by which the pathogen evades host immune responses to the infection.

Role of commensal gut bacteria in inflammatory bowel diseases

Aberrant immune responses toward commensal gut bacteria can result in the onset and perpetuation of inflammatory bowel diseases (IBD). Reduced microbiota diversity in conjunction with lower proportion of Gram positive and higher proportion of Gram negative bacteria than in healthy subjects is frequently reported in IBD patients. In a subset of IBD patients, E. coli strains with specific features trigger disease. Important molecular mechanisms underlying this effect have been identified. However, in the majority of patients the exact nature of host-microbe interactions that contribute to IBD development has so far not been defined. The application of metagenomic techniques may help to identify bacterial functions that are involved in the aggravation or alleviation of IBD. Subsequently, the relevance for disease development of bacterial candidate genes may be tested taking advantage of reductionist animal models of chronic gut inflammation. This approach may help to identify bacterial functions that can be targeted in future concepts of IBD therapy.

The σE pathway is involved in biofilm formation by Crohn's disease-associated adherent-invasive Escherichia coli

Ileal lesions of patients with Crohn's disease are colonized by adherent-invasive Escherichia coli (AIEC) bacteria that are able to adhere to and invade intestinal epithelial cells (IEC), to replicate within macrophages, and to form biofilm. Clinical observations showed that bacterial biofilms were associated with the mucosa of inflammatory bowel disease patients. In the present study, we analyzed the relationship between AIEC colonization of the gut and the formation of biofilm, focusing on the involvement of the σ(E) pathway in the AIEC-IEC interaction. We observed that σ(E) pathway inhibition in AIEC reference strain LF82 led to an impaired ability to adhere to and invade IEC but also induced a large decrease in the abilities to colonize the intestinal mucosa and form biofilm. This indicates that targeting of the σ(E) pathway could be a very potent therapeutic strategy by which to interfere with the ability of AIEC to form biofilm on the gut mucosa of Crohn's disease patients.

AIEC colonization and pathogenicity: influence of previous antibiotic treatment and preexisting inflammation

BACKGROUND

Inflammatory bowel diseases (IBD) patients are abnormally colonized by adherent-invasive Escherichia coli (AIEC). NOD2 gene mutations impair intracellular bacterial clearance. We evaluated the impact of antibiotic treatment on AIEC colonization in wildtype (WT) and NOD2 knockout mice (NOD2KO) and the consequences on intestinal inflammation.

METHODS

After 3 days of antibiotic treatment, mice were infected for 2 days with 10⁹ CFU AIEC and sacrificed 1, 5, and 60 days later. In parallel, mice were challenged with AIEC subsequent to a dextran sodium sulfate (DSS) treatment and sacrificed 9 days later. Ileum, colon, and mesenteric tissues were sampled for AIEC quantification and evaluation of inflammation.

RESULTS

Without antibiotic treatment, AIEC was not able to colonize WT and NOD2KO mice. Compared with nontreated animals, antibiotic treatment led to a significant increase in ileal and colonic colonization of AIEC in WT and/or NOD2KO mice. Persistent AIEC colonization was observed until day 5 only in NOD2KO mice, disappearing at day 60. Mesenteric translocation of AIEC was observed only in NOD2KO mice. No inflammation was observed in WT and NOD2KO mice treated with antibiotics and infected with AIEC. During DSS-induced colitis, colonization and persistence of AIEC was observed in the colon. Moreover, a dramatic increase in clinical, histological, and molecular parameters of colitis was observed in mice infected with AIEC but not with a commensal E. coli strain.

CONCLUSIONS

Antibiotic treatment was necessary for AIEC colonization of the gut and mesenteric tissues and persistence of AIEC was dependent on NOD2. AIEC exacerbated a preexisting DSS-induced colitis in WT mice.

The role of autophagy in Crohn's disease

(Macro)-autophagy is a homeostatic process by which eukaryotic cells dispose of protein aggregates and damaged organelles. Autophagy is also used to degrade micro-organisms that invade intracellularly in a process termed xenophagy. Genome-wide association scans have recently identified autophagy genes as conferring susceptibility to Crohn’s disease (CD), one of the chronic inflammatory bowel diseases, with evidence suggesting that CD arises from a defective innate immune response to enteric bacteria. Here we review the emerging role of autophagy in CD, with particular focus on xenophagy and enteric E. coli strains with an adherent and invasive phenotype that have been consistently isolated from CD patients with ileal disease.

Bile salts induce long polar fimbriae expression favouring Crohn's disease-associated adherent-invasive Escherichia coli interaction with Peyer's patches

Ileal lesions of patients with Crohn's disease are colonized by adherent-invasive Escherichia coli (AIEC). The earliest lesions of recurrent Crohn's disease are erosions of Peyer's patches (PP). We recently reported the presence of a functional lpf operon in AIEC, encoding long polar fimbriae (LPF), that allows AIEC bacteria to interact with PP and to translocate across M cells. The aim of this study was to analyse the effect of gastrointestinal conditions on LPF expression in AIEC strains. The LF82 bacterial growth in an acid pH medium or at high osmolarity medium had no effect on lpf transcription level, in contrast to bacterial growth in the presence of bile salts, which promoted activation of lpf transcription. When cultured in the presence of bile salt, LF82 wild-type bacteria, but not the isogenic mutant deleted for lpfA, exhibited a higher level of interaction with PP and a higher level of translocation through M cell monolayers. The FhlA transcriptional factor was found to be a key bacterial regulator at the origin of LPF expression in the presence of bile salts.

Blastocystis: past pitfalls and future perspectives

Blastocystis is a genetically heterogeneous protist found in the intestinal tract (IT) of many vertebrates, and although it is implicated in a variety of human intestinal disorders, data regarding the clinical relevance of Blastocystis is at best speculative. Several research issues, including a lack of standardization across studies, the potential for intrasubtype variation in pathogenicity, and difficulties associated with diagnostics for many idiopathic disorders of the human IT have led to conflicting reports in support of a role for Blastocystis pathogenicity. Here, several research areas and methodologies are reviewed that if integrated appropriately into a prospective study may prove useful and facilitate a better understanding of the role of Blastocystis in human health and disease.

Lack of Tir ubiquitylation contributes to enteropathogenic E. coli remaining extracellular during nonphagocytic cell infections

Enteropathogenic Escherichia coli (EPEC) is an extracellular pathogen that alters many host subcellular components during its infectious processes. We have previously shown that EPEC hijacks a large assortment of host cell endocytic components and uses these proteins to form protruding structures called "pedestals" rather than triggering internalization of the bacteria. Other invasive pathogens that also recruit similar endocytic components have been shown to enter their host cells on the ubiquitylation of their host cell receptors. Therefore, we hypothesize that EPEC remains extracellular by maintaining its receptor, translocated intimin receptor (Tir), in an unubiquitylated state. Using immunoprecipitation-Western blots, we demonstrate no association of ubiquitin with Tir. To further elucidate the effect Tir ubiquitylation would have on EPEC during their infections, we engineered Tir-ubiquitin fusion constructs, expressed them in host epithelial cells, and infected them with Δtir EPEC. We found these cells induced a significant increase in EPEC invasion as compared with cells that expressed the Tir construct that lacked ubiquitin conjugation. Our results indicate that the lack of EPEC receptor ubiquitylation is a contributing factor that these microbes use to prevent their internalization into epithelial cells.

Characterization of adherent-invasive Escherichia coli isolated from pediatric patients with inflammatory bowel disease

BACKGROUND

Crohn's disease (CD) and ulcerative colitis (UC), known as inflammatory bowel diseases (IBD), are characterized by an abnormal immunological response to commensal bacteria colonizing intestinal lumen and mucosa. Among the latter, strains of adherent-invasive Escherichia coli (AIEC), capable of adhering to and invading epithelium, and to replicate in macrophages, have been described in CD adults. We aimed at identifying and characterizing AIEC strains in pediatric IBD.

METHODS

In all, 24 CD children, 10 UC, and 23 controls were investigated. Mucosal biopsies, taken during colonoscopy, were analyzed for the presence of AIEC strains by an adhesive-invasive test. Protein expression of the specific AIEC receptor, the carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), was evaluated by western blot and immunohistochemistry, while tumor necrosis factor alpha (TNF-α) and interleukin (IL)-8 mRNA expression was detected by real-time polymerase chain reaction (PCR), after bacterial infection. Transmission electron microscopy and trans-epithelial electric resistance assays were performed on biopsies to assess bacteria-induced morphological and functional epithelial alterations.

RESULTS

Two bacterial strains, EC15 and EC10, were found to adhere and invade the Caco2 cell line, similar to the well-known AIEC strain LF82 (positive control): they upregulated CEACAM6, TNF-α, and IL-8 gene/protein expression, in vitro and in cultured intestinal mucosa; they could also survive inside macrophages and damage the epithelial barrier integrity. Lesions in the inflamed tissues were associated with bacterial infection.

CONCLUSIONS

This is the first study showing the presence of adhesive-invasive bacteria strains in the inflamed tissues of children with IBD. Collective features of these strains indicate that they belong to the AIEC spectrum, suggesting their possible role in disease pathogenesis.

Development of a unique small molecule modulator of CXCR4

Background

Metastasis, the spread and growth of tumor cells to distant organ sites, represents the most devastating attribute and plays a major role in the morbidity and mortality of cancer. Inflammation is crucial for malignant tumor transformation and survival. Thus, blocking inflammation is expected to serve as an effective cancer treatment. Among anti-inflammation therapies, chemokine modulation is now beginning to emerge from the pipeline. CXC chemokine receptor-4 (CXCR4) and its ligand stromal cell-derived factor-1 (CXCL12) interaction and the resulting cell signaling cascade have emerged as highly relevant targets since they play pleiotropic roles in metastatic progression. The unique function of CXCR4 is to promote the homing of tumor cells to their microenvironment at the distant organ sites.

Methodology/Principal Findings

We describe the actions of N,N′-(1,4-phenylenebis(methylene))dipyrimidin-2-amine (designated MSX-122), a novel small molecule and partial CXCR4 antagonist with properties quite unlike that of any other reported CXCR4 antagonists, which was prepared in a single chemical step using a reductive amination reaction. Its specificity toward CXCR4 was tested in a binding affinity assay and a ligand competition assay using ¹⁸F-labeled MSX-122. The potency of the compound was determined in two functional assays, Matrigel invasion assay and cAMP modulation. The therapeutic potential of MSX-122 was evaluated in three different murine models for inflammation including an experimental colitis, carrageenan induced paw edema, and bleomycin induced lung fibrosis and three different animal models for metastasis including breast cancer micrometastasis in lung, head and neck cancer metastasis in lung, and uveal melanoma micrometastasis in liver in which CXCR4 was reported to play crucial roles.

Conclusions/Significance

We developed a novel small molecule, MSX-122, that is a partial CXCR4 antagonist without mobilizing stem cells, which can be safer for long-term blockade of metastasis than other reported CXCR4 antagonists.

Infection strategies of enteric pathogenic Escherichia coli

Enteric Escherichia coli (E. coli) are both natural flora of humans and important pathogens causing significant morbidity and mortality worldwide. Traditionally enteric E. coli have been divided into 6 pathotypes, with further pathotypes often proposed. In this review we suggest expansion of the enteric E. coli into 8 pathotypes to include the emerging pathotypes of adherent invasive E. coli (AIEC) and Shiga-toxin producing enteroaggregative E. coli (STEAEC). The molecular mechanisms that allow enteric E. coli to colonize and cause disease in the human host are examined and for two of the pathotypes that express a type 3 secretion system (T3SS) we discuss the complex interplay between translocated effectors and manipulation of host cell signaling pathways that occurs during infection.

Replication of Crohn's disease-associated AIEC within macrophages is dependent on TNF-α secretion

Adherent and invasive Escherichia coli (AIEC) associated with Crohn's disease are able to survive and to replicate extensively in active phagolysosomes within macrophages. AIEC-infected macrophages release large amounts of tumour necrosis factor-alpha (TNF-α) and do not undergo cell death. The aim of the present study was to determine what benefit AIEC bacteria could gain from inducing the release of large amounts of TNF-α by infected macrophages and to what extent the neutralization of TNF-α could affect AIEC intramacrophagic replication. Our results showed that the amount of TNF-α released by infected macrophages is correlated with the load of intramacrophagic AIEC bacteria and their intracellular replication. TNF-α secretion was not related to the number of bacteria entering host cells because when the number of bacteria internalized in macrophage was decreased by blocking lipid raft-dependent and clathrin-coated pits-dependent endocytosis, the amount of TNF-α secreted by infected macrophages was not modified. Interestingly, dose-dependent increases in the number of intracellular AIEC LF82 bacteria were observed when infected macrophages were stimulated with exogenous TNF-α, and neutralization of TNF-α secreted by AIEC-infected macrophages using anti-TNF-α antibodies induced a significant decrease in the number of intramacrophagic bacteria. These results indicate that AIEC bacteria use TNF-α as a Trojan horse to ensure their intracellular replication because replication of AIEC bacteria within macrophages induces the release of TNF-α, which in turn increases the intramacrophagic replication of AIEC. Neutralizing TNF-α secreted by infected macrophages may represent an effective strategy to control AIEC intracellular replication.

Defects in autophagy favour adherent-invasive Escherichia coli persistence within macrophages leading to increased pro-inflammatory response

Ileal lesions in Crohn's disease (CD) patients are abnormally colonized by pathogenic adherent-invasive Escherichia coli (AIEC). AIEC bacteria are able to replicate within epithelial cells after lysis of the endocytic vacuole and within macrophages in a large vacuole. CD-associated polymorphisms in NOD2, ATG16L1 and IRGM affect bacterial autophagy, a crucial innate immunity mechanism. We previously determined that defects in autophagy impaired the ability of epithelial cells to control AIEC replication. AIEC behave differently within epithelial cells and macrophages and so we investigated the impact of defects in autophagy on AIEC intramacrophagic replication and pro-inflammatory cytokine response. AIEC bacteria induced the recruitment of the autophagy machinery at the site of phagocytosis, and functional autophagy limited AIEC intramacrophagic replication. Impaired ATG16L1, IRGM or NOD2 expression induced increased intramacrophagic AIEC and increased secretion of IL-6 and TNF-α in response to AIEC infection. In contrast, forced induction of autophagy decreased the numbers of intramacrophagic AIEC and pro-inflammatory cytokine release, even in a NOD2-deficient context. On the basis of our findings, we speculate that stimulating autophagy in CD patients would be a powerful therapeutic strategy to concomitantly restrain intracellular AIEC replication and slow down the inflammatory response.

IBD-what role do Proteobacteria play?

The gastrointestinal microbiota has come to the fore in the search for the causes of IBD. This shift has largely been driven by the finding of genetic polymorphisms involved in gastrointestinal innate immunity (particularly polymorphisms in NOD2 and genes involved in autophagy) and alterations in the composition of the microbiota that might result in inflammation (so-called dysbiosis). Microbial diversity studies have continually demonstrated an expansion of the Proteobacteria phylum in patients with IBD. Individual Proteobacteria, in particular (adherent-invasive) Escherichia coli, Campylobacter concisus and enterohepatic Helicobacter, have all been associated with the pathogenesis of IBD. In this Review, we comprehensively describe the various associations of Proteobacteria and IBD. We also examine the importance of pattern recognition in the extracellular innate immune response of the host with particular reference to Proteobacteria, and postulate that Proteobacteria with adherent and invasive properties might exploit host defenses, drive proinflammatory change, alter the intestinal microbiota in favor of dysbiosis and ultimately lead to the development of IBD.

IBD-what role do Proteobacteria play?

The gastrointestinal microbiota has come to the fore in the search for the causes of IBD. This shift has largely been driven by the finding of genetic polymorphisms involved in gastrointestinal innate immunity (particularly polymorphisms in NOD2 and genes involved in autophagy) and alterations in the composition of the microbiota that might result in inflammation (so-called dysbiosis). Microbial diversity studies have continually demonstrated an expansion of the Proteobacteria phylum in patients with IBD. Individual Proteobacteria, in particular (adherent-invasive) Escherichia coli, Campylobacter concisus and enterohepatic Helicobacter, have all been associated with the pathogenesis of IBD. In this Review, we comprehensively describe the various associations of Proteobacteria and IBD. We also examine the importance of pattern recognition in the extracellular innate immune response of the host with particular reference to Proteobacteria, and postulate that Proteobacteria with adherent and invasive properties might exploit host defenses, drive proinflammatory change, alter the intestinal microbiota in favor of dysbiosis and ultimately lead to the development of IBD.

Microevolution in fimH gene of mucosa-associated Escherichia coli strains isolated from pediatric patients with inflammatory bowel disease

Several studies reported increased numbers of mucosa-associated Escherichia coli strains in patients with inflammatory bowel disease (IBD), encompassing Crohn's disease (CD) and ulcerative colitis (UC). The majority of E. coli strains possess type 1 fimbriae, whose tip fibrillum protein, FimH, naturally undergoes amino acid replacements, an important process in the adaptation of commensal E. coli strains to environmental changes, like those observed in IBD and urinary tract infections. In this study, we analyzed mutational patterns in the fimH gene of 52 mucosa-associated E. coli strains isolated from IBD and non-IBD pediatric patients, in order to investigate microevolution of this genetic trait. FimH-positive strains were also phylogenetically typed and tested for their adhesive ability on Caco-2 cells. Specific FimH alleles for each grouping feature were found. Mutations G66S and V27A were related to CD, while mutations A242V, V163A, and T74I were attributed to UC. Otherwise, the G66S, N70S, and S78N mutations were specifically attributed to B2/D phylogroups. The N70S and A119V mutations were related to adhesive E. coli strains. Phylogroup B2, adhesive, and IBD E. coli strains showed a higher site substitution rate (SSR) in the fimH gene, together with a higher number of mutations. The degree of naïve mucosal inflammation was related to specific FimH alleles. Moreover, we could suggest that the V27A mutation is pathoadaptive for the CD intestinal habitat, while we could also suggest that both the N70S and S78N mutations are related to the more virulent E. coli B2 phylogroup. In conclusion, we found some FimH variants that seem to be more involved than others in the evolution of IBD pathogenesis.

New molecular insights into inflammatory bowel disease-induced diarrhea

Diarrhea is one of the common symptoms that significantly affects quality of life in patients with inflammatory bowel disease (IBD). The clinical manifestation of diarrhea is mainly dependant on the type of IBD and the location, extent and severity of intestinal inflammation. Understanding the pathophysiologic mechanisms of diarrhea in patients with IBD will be beneficial to developing effective treatments for IBD-associated diarrhea. In recent years, modern molecular techniques have been used intensively to dissect the role of the intestinal microbiota, epithelial barrier and the host immune system in the mechanisms of IBD-induced diarrhea. These studies have significantly advanced our knowledge of the mechanisms of IBD-induced diarrhea. In this article, we focus on the new and critical molecular insights into the contributions of the intestinal microbiota, epithelial tight junctions, proinflammatory cytokines and microRNA as potential mechanisms underlying to IBD-induced diarrhea.

Conversion of commensal Escherichia coli K-12 to an invasive form via expression of a mutant histone-like protein

The HUα^{E38K, V42L} mutant of the bacterial histone-like protein HU causes a major change in the transcription profile of the commensal organism Escherichia coli K-12 (Kar S, Edgar R, Adhya S, Proc. Natl. Acad. Sci. U. S. A. 102:16397–16402, 2005). Among the upregulated genes are several related to pathogenic interactions with mammalian cells, as evidenced by the expression of curli fibers, Ivy, and hemolysin E. When E. coli K-12/ HUα^{E38K, V42L} was added to Int-407 cells, there was host cell invasion, phagosomal disruption, and intracellular replication. The invasive trait was also retained in a murine ileal loop model and intestinal explant assays. In addition to invasion, the internalized bacteria caused a novel subversion of host cell apoptosis through modification and regulation of the BH3-only proteins Bim_EL and Puma. Changes in the transcription profile were attributed to positive supercoiling of DNA leading to the altered availability of relevant promoters. Using the E. coli K-12/HUα^{E38K, V42L} variant as a model, we propose that traditional commensal E. coli can adopt an invasive lifestyle through reprogramming its cellular transcription, without gross genetic changes.

Escherichia coli K-12 is well established as a benign laboratory strain and a human intestinal commensal. Recent evidences, however, indicate that the typical noninvasive nature of resident E. coli can be reversed under specific circumstances even in the absence of any major genomic flux. We previously engineered an E. coli strain with a mutant histone-like protein, HU, which exhibited significant changes in nucleoid organization and global transcription. Here we showed that the changes induced by the mutant HU have critical functional consequences: from a strict extracellular existence, the mutant E. coli adopts an almost obligate intracellular lifestyle. The internalized E. coli exhibits many of the prototypical characteristics of traditional intracellular bacteria, like phagosomal escape, intracellular replication, and subversion of host cell apoptosis. We suggest that E. coli K-12 can switch between widely divergent lifestyles in relation to mammalian host cells by reprogramming its cellular transcription program and without gross changes in its genomic content.

Ex vivo intestinal adhesion of Escherichia coli LF82 in Crohn's disease

Adherent-invasive Escherichia coli (AIEC) are reported to inhabit the gut mucosa in Crohn's disease (CD), however, little is known about the importance of host factors for the interplay between AIEC and the human gut. To examine if differences in bacterial adhesion patterns are disease associated, the AIEC-prototype strain LF82 was evaluated for its ability to adhere to ileal and colonic biopsies from CD and healthy controls (HC). Moreover, the efficacy of the non-pathogenic E. coli Nissle 1917 (ECN) in averting LF82 adhesion to ileal mucosa was assessed. Similar numbers of LF82 adhered to biopsies from CD and HC. A significantly greater LF82 attachment to ileal versus colonic mucosa was found in HC (P < 0.01), however, not in CD. ECN did not reduce the adhesion of LF82 to ileal specimens in CD or HC. These results show that enhanced bacterial adhesion ability is unlikely to play any significant role in CD, thus implying that other host protective factors may be impaired in CD. Further, exclusion of LF82 attachment by ECN co-incubation does not appear to represent a relevant treatment regimen.

Complete genome sequence of the Crohn's disease-associated adherent-invasive Escherichia coli strain HM605

Adherent-invasive Escherichia coli strains are increasingly being associated with intestinal pathologies. Here we present the genome sequence of E. coli HM605, a strain isolated from colonic biopsy specimens of a patient with Crohn's disease.

Role of meprins to protect ileal mucosa of Crohn's disease patients from colonization by adherent-invasive E. coli

Ileal lesions in Crohn's disease (CD) patients are colonized by pathogenic adherent-invasive Escherichia coli (AIEC) able to adhere to and invade intestinal epithelial cells (IEC), and to survive within macrophages. The interaction of AIEC with IEC depends on bacterial factors mainly type 1 pili, flagella, and outer membrane proteins. In humans, proteases can act as host defence mechanisms to counteract bacterial colonization. The protease meprin, composed of multimeric complexes of the two subunits alpha and beta, is abundantly expressed in IECs. Decreased levels of this protease correlate with the severity of the inflammation in patients with inflammatory bowel disease. The aim of the present study was to analyze the ability of meprin to modulate the interaction of AIEC with IECs. In patients with ileal CD we observed decreased levels of meprins, in particular that of meprin β. Dose-dependent inhibition of the abilities of AIEC strain LF82 to adhere to and invade intestinal epithelial T84 cells was observed when bacteria were pre-treated with both exogenous meprin α and meprin β. Dose-dependent proteolytic degradation of type 1 pili was observed in the presence of active meprins, but not with heat-inactivated meprins, and pretreatment of AIEC bacteria with meprins impaired their ability to bind mannosylated host receptors and led to decreased secretion of the pro-inflammatory cytokine IL-8 by infected T84 cells. Thus, decreased levels of protective meprins as observed in CD patients may contribute to increased AIEC colonization.

Comparative genomics of Escherichia coli isolated from patients with inflammatory bowel disease

Background

Inflammatory bowel disease (IBD) is used to describe a state of idiopathic, chronic inflammation of the gastrointestinal tract. The two main phenotypes of IBD are Crohn's disease (CD) and ulcerative colitis (UC). The major cause of IBD-associated mortality is colorectal cancer. Although both host-genetic and exogenous factors have been found to be involved, the aetiology of IBD is still not well understood. In this study we characterized thirteen Escherichia coli strains from patients with IBD by comparative genomic hybridization employing a microarray based on 31 sequenced E. coli genomes from a wide range of commensal and pathogenic isolates.

Results

The IBD isolates, obtained from patients with UC and CD, displayed remarkably heterogeneous genomic profiles with little or no evidence of group-specific determinants. No IBD-specific genes were evident when compared with the prototypic CD isolate, LF82, suggesting that the IBD-inducing effect of the strains is multifactorial. Several of the IBD isolates carried a number of extraintestinal pathogenic E. coli (ExPEC)-related virulence determinants such as the pap, sfa, cdt and hly genes. The isolates were also found to carry genes of ExPEC-associated genomic islands.

Conclusions

Combined, these data suggest that E. coli isolates obtained from UC and CD patients represents a heterogeneous population of strains, with genomic profiles that are indistinguishable to those of ExPEC isolates. Our findings indicate that IBD-induction from E. coli strains is multifactorial and that a range of gene products may be involved in triggering the disease.

Analysis of Escherichia coli isolated from patients affected by Crohn's disease

The etiopathogenesis of Crohn's disease (CD) is still controversial: several genetic, immunologic, and environmental factors, including some bacteria, have been implicated. This study has been devised to assess the involvement of Escherichia coli in CD. Seven E. coli strains were isolated from 14 biopsies obtained from ileocolic ulcers of patients affected by inflammatory bowel disease (IBD), including six with ulcerative colitis and eight with CD. Five strains, exclusively isolated from CD patients, were found inside mucosal cells. Different PCR techniques (for chuA, yjaA, TspE4.C2, escV, and bfpB genes) were performed and PFGE was carried out to characterize these bacteria in comparison with other E. coli strains isolated from non-IBD specimens. The correlation of these characters with bacterial invasiveness on intestinal (Caco-2) and phagocytic (U937) cells was assessed. Overall our pilot data suggest that five among eight strains isolated from CD patients belonged to the adherent-invasive E. coli (AIEC) group, and were invasive on Caco-2 cells and resistant to phagocytosis. These findings suggest that these bacteria could be considered target organisms whose elimination could reduce the intestinal inflammatory process and CD progression.

High prevalence of aggregative adherent Escherichia coli strains in the mucosa-associated microbiota of patients with inflammatory bowel diseases

The intestinal population of Escherichia coli is increased in patients with inflammatory bowel disease (IBD), but the reason for this elevation, the particular features of these bacteria and their potential role in the pathogenesis of the disease are not known. The present study was undertaken to investigate the adherence abilities and some virulence properties of a collection of 131 E. coli isolates cultured from rectal biopsies of 23 subjects diagnosed with ulcerative colitis (UC), 8 with Crohn's disease (CD) and 23 control patients from southern Brazil. The adherence abilities of the bacteria were investigated in vitro, using HEp-2 epithelial cells in assays of 3 and 6h of bacteria-cell contact. The isolates were screened by PCR with primers for the following virulence genetic markers: plasmid of aggregative adhesion (pAA) and the aggregative adherence fimbriae R (aggR), E. coli attaching and effacing (eae), invasion-associated locus (ial), invasion plasmid antigen H (ipaH) and Shiga citotoxin-encoding (stx) genes. HEp-2 cells aggregative adherent E. coli strains, as detected in the 3h adherence assay, were found in 14/23 (60.9%) patients with UC, 7/8 (87.5%) with CD and in 7/23 (30.4%) controls (p=0.011). Virulence genetic markers were detected in strains of 9 patients with UC (39.1%), but in none of CD or control group. Two of these UC patients had strains harboring both pAA and aggR, one had strains positive for aggR, four had strains positive for eae and two had strains positive for stx. These results suggest that the augmented population of E. coli on the rectal mucosa of IBD patients, particularly of those diagnosed with UC, is mostly comprised of aggregative adherent strains, some of which possessing classical virulence markers of E. coli.

The commensal microbiota and enteropathogens in the pathogenesis of inflammatory bowel diseases

Intestinal inflammation arises from abnormal host-microbe interactions. The perturbations of homeostatic coexistence involve host genetic factors, barrier function, innate and adaptive immunity, as well as qualitative and quantitative changes in the composition of the microbiota. Dysbiosis toward selected micro-organisms and decreased complexity of commensal bacteria have been observed in patients with Crohn's disease and ulcerative colitis, but it is not clear whether the dysbiosis contributes to development of inflammatory bowel disease or is instead a consequence of the disease. Pathogens with virulence factors that allow them to breach the intestinal barrier and induce chronic inflammation might mediate the pathogenesis of these diseases. To identify new therapeutic approaches for inflammatory bowel disease, it is important to identify host susceptibility factors involved in the control of microbial infection, characterize potential pathogens, and eliminate them or block the expression of their virulence factors.

CEACAM6 gene variants in inflammatory bowel disease

BACKGROUND

The carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) acts as a receptor for adherent-invasive E. coli (AIEC) and its ileal expression is increased in patients with Crohn's disease (CD). Given its contribution to the pathogenesis of CD, we aimed to investigate the role of genetic variants in the CEACAM6 region in patients with inflammatory bowel diseases (IBD).

METHODOLOGY

In this study, a total of 2,683 genomic DNA samples (including DNA from 858 CD patients, 475 patients with ulcerative colitis (UC), and 1,350 healthy, unrelated controls) was analyzed for eight CEACAM6 SNPs (rs10415946, rs1805223 = p.Pro42Pro, rs4803507, rs4803508, rs11548735 = p.Gly239Val, rs7246116 = pHis260His, rs2701, rs10416839). In addition, a detailed haplotype analysis and genotype-phenotype analysis were performed. Overall, our genotype analysis did not reveal any significant association of the investigated CEACAM6 SNPs and haplotypes with CD or UC susceptibility, although certain CEACAM6 SNPs modulated CEACAM6 expression in intestinal epithelial cell lines. Despite its function as receptor of AIEC in ileal CD, we found no association of the CEACAM6 SNPs with ileal or ileocolonic CD. Moreover, there was no evidence of epistasis between the analyzed CEACAM6 variants and the main CD-associated NOD2, IL23R and ATG16L1 variants.

CONCLUSIONS

This study represents the first detailed analysis of CEACAM6 variants in IBD patients. Despite its important role in bacterial attachment in ileal CD, we could not demonstrate a role for CEACAM6 variants in IBD susceptibility or regarding an ileal CD phenotype. Further functional studies are required to analyze if these gene variants modulate ileal bacterial attachment.

Quantification of specific E. coli in gut mucosa from Crohn's disease patients

We here present a method based on qRT-PCR to quantify E. coli LF82 in intestinal human samples. Two different primer-probe sets were designed to detect LF82, and a third to target total E. coli. The assay showed high robustness and specificity for detection of LF82 in the presence of intestinal tissue.

Crohn disease: a current perspective on genetics, autophagy and immunity

Crohn disease (CD) is a chronic and debilitating inflammatory condition of the gastrointestinal tract. Prevalence in Western populations is 100-150/100,000 and somewhat higher in Ashkenazi Jews. Peak incidence is in early adult life, although any age can be affected and a majority of affected individuals progress to relapsing and chronic disease. Medical treatments rely significantly on empirical corticosteroid therapy and immunosuppression, and intestinal resectional surgery is frequently required. Thus, 80% of patients with CD come to surgery for refractory disease or complications. It is hoped that an improved understanding of pathogenic mechanisms, for example by studying the genetic basis of CD and other forms of inflammatory bowel diseases (IBD), will lead to improved therapies and possibly preventative strategies in individuals identified as being at risk.

Crohn disease: a current perspective on genetics, autophagy and immunity

Crohn disease (CD) is a chronic and debilitating inflammatory condition of the gastrointestinal tract. Prevalence in Western populations is 100-150/100,000 and somewhat higher in Ashkenazi Jews. Peak incidence is in early adult life, although any age can be affected and a majority of affected individuals progress to relapsing and chronic disease. Medical treatments rely significantly on empirical corticosteroid therapy and immunosuppression, and intestinal resectional surgery is frequently required. Thus, 80% of patients with CD come to surgery for refractory disease or complications. It is hoped that an improved understanding of pathogenic mechanisms, for example by studying the genetic basis of CD and other forms of inflammatory bowel diseases (IBD), will lead to improved therapies and possibly preventative strategies in individuals identified as being at risk.

The role of bacteria and pattern-recognition receptors in Crohn's disease

Crohn's disease is widely regarded as a multifactorial disease, and evidence from human and animal studies suggests that bacteria have an instrumental role in its pathogenesis. Comparison of the intestinal microbiota of patients with Crohn's disease to that of healthy controls has revealed compositional changes. In most studies these changes are characterized by an increase in the abundance of Bacteroidetes and Proteobacteria and a decrease in that of Firmicutes. In addition, a number of specific mucosa-associated bacteria have been postulated to have a role in Crohn's disease, including Mycobacterium avium subspecies paratuberculosis, adherent and invasive Escherichia coli, Campylobacter and Helicobacter species. The association between mutations in pattern-recognition receptors (Toll-like receptors and Nod-like receptors) and autophagy proteins and Crohn's disease provides further evidence to suggest that defective sensing and killing of bacteria may drive the onset of disease. In this Review, we present recent advances in understanding the role of bacteria and the contribution of pattern-recognition receptors and autophagy in the pathogenesis of Crohn's disease.

Crohn disease--associated adherent-invasive E. coli bacteria target mouse and human Peyer's patches via long polar fimbriae

Crohn disease (CD) is a multifactorial disease in which an abnormal immune response in the gastrointestinal (GI) tract leads to chronic inflammation. The small intestine, particularly the ileum, of patients with CD is colonized by adherent-invasive E. coli (AIEC)--a pathogenic group of E. coli able to adhere to and invade intestinal epithelial cells. As the earliest inflammatory lesions are microscopic erosions of the epithelium lining the Peyer's patches (PPs), we investigated the ability of AIEC bacteria to interact with PPs and the virulence factors involved. We found that AIEC bacteria could interact with mouse and human PPs via long polar fimbriae (LPF). An LPF-negative AIEC mutant was highly impaired in its ability to interact with mouse and human PPs and to translocate across monolayers of M cells, specialized epithelial cells at the surface of PPs. The prevalence of AIEC strains harboring the lpf operon was markedly higher in CD patients compared with controls. In addition, increased numbers of AIEC, but not LPF-deficient AIEC, bacteria were found interacting with PPs from Nod2(-/-) mice compared with WT mice. In conclusion, we have identified LPF as a key factor for AIEC to target PPs. This could be the missing link between AIEC colonization and the presence of early lesions in the PPs of CD patients.

Microbiotal influence on T cell subset development

The mammalian alimentary tract harbors hundreds of bacterial species that constitute the indigenous microbial flora. The indigenous microbial flora has long been appreciated for its role in host immune system development. Recent reports suggest that components of the microbial flora differentially affect the proportion and number of functionally distinct subsets of T cells in the intestine. Substantial changes in the composition of the microbiota are associated with inflammatory bowel disease. This review will discuss the importance of individual species of microbial flora in the induction of T cell subsets, particularly Th17 cells and regulatory T (Treg) cells in the intestine.

A synonymous variant in IRGM alters a binding site for miR-196 and causes deregulation of IRGM-dependent xenophagy in Crohn's disease

Susceptibility to Crohn's disease, a complex inflammatory disease, is influenced by common variants at many loci. The common exonic synonymous SNP (c.313C>T) in IRGM, found in strong linkage disequilibrium with a deletion polymorphism, has been classified as non-causative because of the absence of an alteration in the IRGM protein sequence or splice sites. Here we show that a family of microRNAs (miRNAs), miR-196, is overexpressed in the inflammatory intestinal epithelia of individuals with Crohn's disease and downregulates the IRGM protective variant (c.313C) but not the risk-associated allele (c.313T). Subsequent loss of tight regulation of IRGM expression compromises control of intracellular replication of Crohn's disease-associated adherent invasive Escherichia coli by autophagy. These results suggest that the association of IRGM with Crohn's disease arises from a miRNA-based alteration in IRGM regulation that affects the efficacy of autophagy, thereby implicating a synonymous polymorphism as a likely causal variant.

A role for the RNA chaperone Hfq in controlling adherent-invasive Escherichia coli colonization and virulence

Adherent-invasive Escherichia coli (AIEC) has been linked with the onset and perpetuation of inflammatory bowel diseases. The AIEC strain LF82 was originally isolated from an ileal biopsy from a patient with Crohn's disease. The pathogenesis of LF82 results from its abnormal adherence to and subsequent invasion of the intestinal epithelium coupled with its ability to survive phagocytosis by macrophages once it has crossed the intestinal barrier. To gain further insight into AIEC pathogenesis we employed the nematode Caenorhabditis elegans as an in vivo infection model. We demonstrate that AIEC strain LF82 forms a persistent infection in C. elegans, thereby reducing the host lifespan significantly. This host killing phenotype was associated with massive bacterial colonization of the nematode intestine and damage to the intestinal epithelial surface. C. elegans killing was independent of known LF82 virulence determinants but was abolished by deletion of the LF82 hfq gene, which encodes an RNA chaperone involved in mediating posttranscriptional gene regulation by small non-coding RNAs. This finding reveals that important aspects of LF82 pathogenesis are controlled at the posttranscriptional level by riboregulation. The role of Hfq in LF82 virulence was independent of its function in regulating RpoS and RpoE activity. Further, LF82Δhfq mutants were non-motile, impaired in cell invasion and highly sensitive to various chemical stress conditions, reinforcing the multifaceted function of Hfq in mediating bacterial adaptation. This study highlights the usefulness of simple non-mammalian infection systems for the identification and analysis of bacterial virulence factors.

TLR5 activation induces secretory interleukin-1 receptor antagonist (sIL-1Ra) and reduces inflammasome-associated tissue damage

Toll-like receptor-5 (TLR5)-mediated detection of flagellin induces nuclear factor (NF)-κB-mediated transcription of host defense gene expression, whereas recognition of intracellular flagellin by interleukin (IL)-1-converting enzyme protease-activation factor (IPAF) results in maturation/secretion of the inflammasome cytokine IL-1β. The potent effects of IL-1β are counter-regulated by secretory IL-1 receptor antagonist (sIL-1Ra). We studied the roles of flagellin receptors in regulating the expression of IL-1β and sIL-1Ra and their subsequent roles in inflammation. Flagellin induced sIL-1Ra in intestinal epithelia and macrophages in a dose- and time-dependent manner, whereas IL-1β was only induced in macrophages. In vivo, flagellin-induced sIL-1Ra, but not IL-1β, was absolutely dependent upon TLR5 expressed on non-hemopioetic cells. Thus, loss of TLR5 increased the IL-1β/sIL-1Ra ratio on flagellin treatment, which correlated with increased inflammatory pathology in response to this product. Furthermore, the flagellin/TLR5 interaction was important for the induction of sIL-1Ra and limiting inflammatory pathology on Salmonella infection. Finally, reduced sIL-1Ra levels in TLR5KO mice correlated with spontaneous colitis. Taken together, we demonstrate that intestinal epithelia, despite not expressing IL-1β, secrete sIL-1Ra in a TLR5-dependent manner suggesting that loss of TLR5 may promote inflammation by increasing IL-1β activity. Thus, optimizing the balance between inflammasome cytokines and their endogenous inhibitors might prove a useful strategy to treat inflammatory disorders.

Bacterial induction of proinflammatory cytokines in inflammatory bowel disease

It has become increasingly clear that inflammatory bowel disease (IBD) develops on the background of genetic defects in the host, conveying an increased susceptibility to an environmental antigen or antigens. The environmental factor implicated in the pathophysiology of gut inflammation, which is undergoing increased scrutiny, is the intestinal flora. The intestinal flora as a whole and specific bacteria and their products have been found to trigger cytokine expression in various cell types. Consistently, multiple bacterial strains were found to induce tumor necrosis factor alpha (TNF-α) and interleukin-8 (IL-8) in macrophage and epithelial cell systems, respectively, in particular in Crohn's disease. Interestingly, various cell types from patients with IBD display an increased susceptibility to specific bacterial products, including flagellin, pili, and lipopolysaccharides. It remains to be determined whether additional effector proteins regulate cytokine expression and the aberrant mucosal immune response in IBD.

Editorial: Antibiotics earlier, IBD later?

Increasing evidence accumulates for a role of environmental factors in the onset of inflammatory bowel diseases (IBD). Among them, factors that might disturb the gut microflora hold an important place. As such, antibiotics deserve a special attention, and a possible association between their use, particularly during childhood, and the development of IBD, has been assessed by several authors since 1987. Results, conclusions, and possible impact of their observations, as well as perspectives for the future, are discussed here, in view of the article published in this issue of the Journal by Shaw et al.

Genome sequence of adherent-invasive Escherichia coli and comparative genomic analysis with other E. coli pathotypes

Background

Adherent and invasive Escherichia coli (AIEC) are commonly found in ileal lesions of Crohn's Disease (CD) patients, where they adhere to intestinal epithelial cells and invade into and survive in epithelial cells and macrophages, thereby gaining access to a typically restricted host niche. Colonization leads to strong inflammatory responses in the gut suggesting that AIEC could play a role in CD immunopathology. Despite extensive investigation, the genetic determinants accounting for the AIEC phenotype remain poorly defined. To address this, we present the complete genome sequence of an AIEC, revealing the genetic blueprint for this disease-associated E. coli pathotype.

Results

We sequenced the complete genome of E. coli NRG857c (O83:H1), a clinical isolate of AIEC from the ileum of a Crohn's Disease patient. Our sequence data confirmed a phylogenetic linkage between AIEC and extraintestinal pathogenic E. coli causing urinary tract infections and neonatal meningitis. The comparison of the NRG857c AIEC genome with other pathogenic and commensal E. coli allowed for the identification of unique genetic features of the AIEC pathotype, including 41 genomic islands, and unique genes that are found only in strains exhibiting the adherent and invasive phenotype.

Conclusions

Up to now, the virulence-like features associated with AIEC are detectable only phenotypically. AIEC genome sequence data will facilitate the identification of genetic determinants implicated in invasion and intracellular growth, as well as enable functional genomic studies of AIEC gene expression during health and disease.

Escherichia coli O25b-ST131: a pandemic, multiresistant, community-associated strain

Escherichia coli sequence type 131 (ST131) is a worldwide pandemic clone, causing predominantly community-onset antimicrobial-resistant infection. Its pandemic spread was identified in 2008 by utilizing multilocus sequence typing (MLST) of CTX-M-15 extended-spectrum β-lactamase-producing E. coli from three continents. Subsequent research has confirmed the worldwide prevalence of ST131 harbouring a broad range of virulence and resistance genes on a transferable plasmid. A high prevalence of the clone (∼30%-60%) has been identified amongst fluoroquinolone-resistant E. coli. In addition, it potentially harbours a variety of β-lactamase genes; most often, these include CTX-M family β-lactamases, and, less frequently, TEM, SHV and CMY β-lactamases. Our knowledge of ST131's geographical distribution is incomplete. A broad distribution has been demonstrated amongst antimicrobial-resistant E. coli from human infection in Europe (particularly the UK), North America, Canada, Japan and Korea. High rates are suggested from limited data in Asia, the Middle East and Africa. The clone has also been detected in companion animals, non-companion animals and foods. The clinical spectrum of disease described is similar to that for other E. coli, with urinary tract infection predominant. This can range from cystitis to life-threatening sepsis. Infection occurs in humans of all ages. Therapy must be tailored to the antimicrobial resistance phenotype of the infecting isolate and the site of infection. Phenotypic detection of the ST131 clone is not possible and DNA-based techniques, including MLST and PCR, are described.

Eating the enemy in Crohn's disease: an old theory revisited

Several old and new observations suggest the existence in Crohn's disease of a phagocytic disorder of macrophages related to impaired bactericidal activity of host cells or to the presence of invasive bacteria that have developed strategies to counteract macrophage killing. It was recently reported that disordered macrophage cytokine secretion underlies impaired acute inflammation and bacterial clearance in Crohn's disease. Secretion of proinflammatory cytokines by CD macrophages was impaired in response to E. coli or specific Toll-like receptor agonists. In addition, major advances in the etiology of Crohn's disease came from the existence of polymorphism in NOD2 and autophagy-related susceptibility genes (ATG16L1 and IRGM) in patients and from the identification of the presence of adherent-invasive E. coli (AIEC) colonizing the CD ileal mucosa and able to resist to macrophage killing. The role of impaired autophagy in Crohn's disease patients has been recently reinforced by the observation that the peptidoglycan receptor NOD2, in addition to sense intracellular bacteria, can induce autophagy by recruiting the critical autophagy protein ATG16L1 to the plasma membrane during bacterial internalization. Defects in autophagy might be the key element of the pathogenic pathway that lead to defective microbial killing, increased exposure to commensal and pathogenic intestinal bacteria and T cell activation. Defects in Paneth cells secreting lysozyme and antimicrobial peptides are observed in patients with ATG16L1 risk allele. Thus, the induction of autophagy or administration of preparations that mirrors the secretion of Paneth cells or both may be regarded as new therapeutic avenues for the treatment of Crohn's disease.

Abnormally expressed ER stress response chaperone Gp96 in CD favours adherent-invasive Escherichia coli invasion

BACKGROUND AND AIMS

Crohn's disease (CD) ileal lesions are colonised by pathogenic adherent-invasive Escherichia coli (AIEC) producing outer membrane vesicles (OMVs) that contribute to the bacterial invasion process. In addition, increased expression of endoplasmic reticulum (ER)-localised stress response proteins, due to ER stress, is observed in patients with CD. The expression of the ER-localised stress response protein Gp96 in patients with CD and its biological role with regards to the ability of AIEC to invade intestinal epithelial cells were analysed.

METHODS AND RESULTS

Immunohistochemistry on tissue arrays showed that, together with CEACAM6 (carcinoembryonic antigen-related cell adhesion molecule 6) or the ER stress protein Grp78, Gp96 is also strongly expressed at the apical plasma membrane of the ileal epithelial cells of 50% of patients with CD. Invasion experiments in the presence of antibodies raised against Gp96, or after transfection of Intestine-407 cells with gp96 small interfering RNA (siRNA), indicated that Gp96 is essential to promote AIEC LF82 invasion, allowing, via the recognition of the outer membrane protein OmpA, OMVs to fuse with intestinal epithelial cells.

CONCLUSIONS

Gp96 is overexpressed on the apical surface of ileal epithelial cells in patients with CD and acts as a host cell receptor for OMVs, promoting AIEC invasion. From the results shown here, it is speculated that AIEC could take advantage of the abnormal expression of Gp96 in patients with CD to invade the ileal mucosa.

Translocation of Crohn's disease Escherichia coli across M-cells: contrasting effects of soluble plant fibres and emulsifiers

BACKGROUND

Crohn's disease is common in developed nations where the typical diet is low in fibre and high in processed food. Primary lesions overlie Peyer's patches and colonic lymphoid follicles where bacterial invasion through M-cells occurs. We have assessed the effect of soluble non-starch polysaccharide (NSP) and food emulsifiers on translocation of Escherichia coli across M-cells.

METHODS

To assess effects of soluble plant fibres and food emulsifiers on translocation of mucosa-associated E coli isolates from Crohn's disease patients and from non-Crohn's controls, we used M-cell monolayers, generated by co-culture of Caco2-cl1 and Raji B cells, and human Peyer's patches mounted in Ussing chambers.

RESULTS

E coli translocation increased across M-cells compared to parent Caco2-cl1 monocultures; 15.8-fold (IQR 6.2-32.0) for Crohn's disease E coli (N=8) and 6.7-fold (IQR 3.7-21.0) for control isolates (N=5). Electron microscopy confirmed E coli within M-cells. Plantain and broccoli NSP markedly reduced E coli translocation across M-cells at 5 mg/ml (range 45.3-82.6% inhibition, p<0.01); apple and leek NSP had no significant effect. Polysorbate-80, 0.01% vol/vol, increased E coli translocation through Caco2-cl1 monolayers 59-fold (p<0.05) and, at higher concentrations, increased translocation across M-cells. Similarly, E coli translocation across human Peyer's patches was reduced 45±7% by soluble plantain NSP (5 mg/ml) and increased 2-fold by polysorbate-80 (0.1% vol/vol).

CONCLUSIONS

Translocation of E coli across M-cells is reduced by soluble plant fibres, particularly plantain and broccoli, but increased by the emulsifier Polysorbate-80. These effects occur at relevant concentrations and may contribute to the impact of dietary factors on Crohn's disease pathogenesis.

The role of bacteria in the pathogenesis of inflammatory bowel disease

Crohn's disease (CD) and ulcerative colitis (UC) have features that suggest bacterial involvement, and all genetic models of inflammatory bowel disease (IBD) require the presence of commensal bacteria. CD is associated with innate immune response genes such as NOD2/CARD15 and the autophagy genes ATG16L1 and IRGM. However, IBD responds to immunosuppression, suggesting that any bacteria involved are not acting as conventional pathogens. Molecular techniques are rapidly advancing our knowledge of the gut microbiota. In CD there is reduced diversity, and notably a reduction in the probiotic Faecalibacterium prausnitzii, the presence of which in the terminal ileum is associated with a reduced risk of recurrence following surgery. There is also a consistent increase in mucosa-associated Escherichia coli with an "adherent and invasive" phenotype, which allows them to replicate inside macrophages and induce granulomas. Speculation that CD could be caused by the Mycobacterium avium subspecies paratuberculosis (MAP) continues. The response to antitumor necrosis factor treatments suggests that, if relevant at all, MAP is not acting as a conventional pathogen. However, there is increased colonization by MAP in CD, and there is evidence that it could have an indirect effect mediated by the suppression of macrophage function. UC relapse is frequently associated with infection by pathogens, but there is less evidence for involvement of a specific bacterial species. Poor barrier integrity followed by an inflammatory reaction to bacterial components, with chronicity maintained by an autoimmune process, seems a plausible pathogenic model. Bacterial theories of pathogenesis are now becoming testable by targeted therapeutic interventions.

Complete genome sequence of Crohn's disease-associated adherent-invasive E. coli strain LF82

BACKGROUND

Ileal lesions of Crohn's disease (CD) patients are abnormally colonized by pathogenic adherent-invasive Escherichia coli (AIEC) able to invade and to replicate within intestinal epithelial cells and macrophages.

PRINCIPAL FINDINGS

We report here the complete genome sequence of E. coli LF82, the reference strain of adherent-invasive E. coli associated with ileal Crohn's disease. The LF82 genome of 4,881,487 bp total size contains a circular chromosome with a size of 4,773,108 bp and a plasmid of 108,379 bp. The analysis of predicted coding sequences (CDSs) within the LF82 flexible genome indicated that this genome is close to the avian pathogenic strain APEC_01, meningitis-associated strain S88 and urinary-isolated strain UTI89 with regards to flexible genome and single nucleotide polymorphisms in various virulence factors. Interestingly, we observed that strains LF82 and UTI89 adhered at a similar level to Intestine-407 cells and that like LF82, APEC_01 and UTI89 were highly invasive. However, A1EC strain LF82 had an intermediate killer phenotype compared to APEC-01 and UTI89 and the LF82 genome does not harbour most of specific virulence genes from ExPEC. LF82 genome has evolved from those of ExPEC B2 strains by the acquisition of Salmonella and Yersinia isolated or clustered genes or CDSs located on pLF82 plasmid and at various loci on the chromosome.

CONCLUSION

LF82 genome analysis indicated that a number of genes, gene clusters and pathoadaptative mutations which have been acquired may play a role in virulence of AIEC strain LF82.

Abnormalities in the handling of intracellular bacteria in Crohn's disease

Ileal lesions in Crohn's disease (CD) patients are colonized by pathogenic adherent-invasive Escherichia coli (AIEC) able to invade and to replicate within intestinal epithelial cells. Recent advances have highlighted the importance of the innate immune system and the critical relationship between the gut flora and the intestinal mucosa. Several combinations of genetic predisposing factors to CD have been described, with the most significant replicable associations including genes for intracellular receptor of bacterial cell walls (NOD2/CARD15), and for bacterial clearance and antigen processing through autophagy (ATG16L1 and IRGM). We recently reported that in IRGM and ATG16L1 deficient cells, intracellular AIEC LF82 bacteria have enhanced replication and that autophagy deficiency surprisingly did not interfere with the ability of intracellular bacteria to survive and/or replicate for any other E. coli strains tested, including nonpathogenic, environmental, commensal, or pathogenic strains involved in gastroenteritis. As autophagy is an innate defense mechanism acting as a cell-autonomous system for elimination of intracellular pathogens, these findings lead weight to the notion that intracellular bacteria including AIEC might play a role in CD pathogenesis.

NlpI contributes to Escherichia coli K1 strain RS218 interaction with human brain microvascular endothelial cells

Escherichia coli K1 is the most common Gram-negative bacillary organism causing neonatal meningitis. E. coli K1 binding to and invasion of human brain microvascular endothelial cells (HBMECs) is a prerequisite for its traversal of the blood-brain barrier (BBB) and penetration into the brain. In the present study, we identified NlpI as a novel bacterial determinant contributing to E. coli K1 interaction with HBMECs. The deletion of nlpI did not affect the expression of the known bacterial determinants involved in E. coli K1-HBMEC interaction, such as type 1 fimbriae, flagella, and OmpA, and the contribution of NlpI to HBMECs binding and invasion was independent of those bacterial determinants. Previous reports have shown that the nlpI mutant of E. coli K-12 exhibits growth defect at 42 degrees C at low osmolarity, and its thermosensitive phenotype can be suppressed by a mutation on the spr gene. The nlpI mutant of strain RS218 exhibited similar thermosensitive phenotype, but additional spr mutation did not restore the ability of the nlpI mutant to interact with HBMECs. These findings suggest the decreased ability of the nlpI mutant to interact with HBMECs is not associated with the thermosensitive phenotype. NlpI was determined as an outer membrane-anchored protein in E. coli, and the nlpI mutant was defective in cytosolic phospholipase A(2)alpha (cPLA(2)alpha) phosphorylation compared to the parent strain. These findings illustrate the first demonstration of NlpI's contribution to E. coli K1 binding to and invasion of HBMECs, and its contribution is likely to involve cPLA(2)alpha.