Campylobacter jejuni response to human mucin MUC2: modulation of colonization and pathogenicity determinants

Vibrio cholerae represses polysaccharide synthesis to promote motility in mucosa

The viscoelastic mucus layer of gastrointestinal tracts is a host defense barrier that a successful enteric pathogen, such as Vibrio cholerae, must circumvent. V. cholerae, the causative agent of cholera, is able to penetrate the mucosa and colonize the epithelial surface of the small intestine. In this study, we found that mucin, the major component of mucus, promoted V. cholerae movement on semisolid medium and in liquid medium. A genome-wide screen revealed that Vibrio polysaccharide (VPS) production was inversely correlated with mucin-enhanced motility. Mucin adhesion assays indicated that VPS bound to mucin. Moreover, we found that vps expression was reduced upon exposure to mucin. In an infant mouse colonization model, mutants that overexpressed VPS colonized less effectively than wild-type strains in more distal intestinal regions. These results suggest that V. cholerae is able to sense mucosal signals and modulate vps expression accordingly so as to promote fast motion in mucus, thus allowing for rapid spread throughout the intestines.

Campylobacter jejuni infection suppressed Cl⁻ secretion induced by CFTR activation in T-84 cells

Campylobacter jejuni causes foodborne disease associated with abdominal pain, gastroenteritis, and diarrhea. These symptoms are induced by bacterial adherence and invasion of host epithelial cells. C. jejuni infection can occur with a low infective dose, suggesting that C. jejuni may have evolved strategies to cope with the bacterial clearance system in the gastrointestinal tract. The mucosa layer is the first line of defense against bacteria. Mucus conditions are maintained by water and anion (especially Cl(-)) movement. Cystic fibrosis transmembrane conductance regulator (CFTR) is the main Cl(-) channel transporting Cl(-) to the lumen. Mutations in CFTR result in dehydrated secreted mucus and bacterial accumulation in the lungs, and recent studies suggest that closely related pathogenic bacteria also may survive in the intestine. However, the relationship between C. jejuni infection and CFTR has been little studied. Here, we used an (125)I(-) efflux assay and measurement of short-circuit current to measure Cl(-) secretion in C. jejuni-infected T-84 human intestinal epithelial cells. The basic state of Cl(-) secretion was unchanged by C. jejuni infection, but CFTR activator was observed to induce Cl(-) secretion suppressed in C. jejuni-infected T-84 cells. The suppression of activated Cl(-) secretion was bacterial dose-dependent and duration-dependent. A similar result was observed during infection with other C. jejuni strains. The mechanism of suppression may occur by affecting water movement or mucus condition in the intestinal tract. A failure of mucus barrier function may promote bacterial adhesion or invasion of host intestinal epithelial cells, thereby causing bacterial preservation in the host intestinal tract.

Comparative proteomic label-free analysis of Campylobacter jejuni NCTC 11168 cultured with porcine mucin

Campylobacter jejuni is a major gastrointestinal pathogen in humans. Poultry is a primary reservoir for C. jejuni, and C. jejuni appears to be highly adapted to the gastrointestinal tracts of avian species. We determined the protein expression profiles of C. jejuni NCTC 11168 cultured in medium containing porcine mucin. Differentially expressed proteins in the presence and absence of porcine mucin were identified using the label-free method. We identified 52 proteins with expression that was either upregulated (32 proteins) or downregulated (20 proteins) by porcine mucin. These proteins are involved in diverse cellular functions, such as motility, cell wall synthesis, iron transport, energy production, and amino acid metabolism. In particular, the upregulated proteins were involved in chemotaxis (CheV and CetA), motility (FlaA), colonization and adherence (CadF, FrdA, CfrA, MapA, and HydA), and stress tolerance (TrxB and ClpB). These results suggest that C. jejuni changes its protein expression in response to porcine mucin and that this change in expression may contribute to host adaptation of C. jejuni NCTC 11168.

Interaction of microbes with mucus and mucins: recent developments

Due to the recent rapid expansion in our understanding of the composition of the gut microflora and the consequences of altering that composition the question of how bacteria colonise mucus layers and interact with components of mucus, such as mucin, is now receiving widespread attention. Using a combination of mucus secreting cells, and a novel mucin microarray platform containing purified native mucins from different sources we recently demonstrated that two gastrointestinal pathogens, Helicobacter pylori and Campylobacter jejuni, colonise mucus by different mechanisms. This result emphasizes the potential for even closely related bacteria to interact with mucus in divergent ways to establish successful infection. Expanding the use of the mucin arrays described in the study to other microorganisms, both pathogenic and commensal, should lead to the discovery of biologically important motifs in bacterial-host interactions and complement the use of novel in vitro cell models, such as mucus secreting cell lines.

The mucin Muc2 limits pathogen burdens and epithelial barrier dysfunction during Salmonella enterica serovar Typhimurium colitis

Salmonella enterica serovar Typhimurium is a model organism used to explore the virulence strategies underlying Salmonella pathogenesis. Although intestinal mucus is the first line of defense in the intestine, its role in protection against Salmonella is still unclear. The intestinal mucus layer is composed primarily of the Muc2 mucin, a heavily O-glycosylated glycoprotein. The core 3-derived O-glycans of Muc2 are synthesized by core 3 β1,3-N-acetylglucosaminyltransferase (C3GnT). Mice lacking these glycans still produce Muc2 but display a thinner intestinal mucus barrier. We began our investigations by comparing Salmonella-induced colitis and mucus dynamics in Muc2-deficient (Muc2(-/-)) mice, C3GnT(-/-) mice, and wild-type C57BL/6 (WT) mice. Salmonella infection led to increases in luminal Muc2 secretion in WT and C3GnT(-/-) mice. When Muc2(-/-) mice were infected with Salmonella, they showed dramatic susceptibility to infection, carrying significantly higher cecal and liver pathogen burdens, and developing significantly higher barrier disruption and higher mortality rates, than WT mice. We found that the exaggerated barrier disruption in infected Muc2(-/-) mice was invA dependent. We also tested the susceptibility of C3GnT(-/-) mice and found that they carried pathogen burdens similar to those of WT mice but developed exaggerated barrier disruption. Moreover, we found that Muc2(-/-) mice were impaired in intestinal alkaline phosphatase (IAP) expression and lipopolysaccharide (LPS) detoxification activity in their ceca, potentially explaining their high mortality rates during infection. Our data suggest that the intestinal mucus layer (Muc2) and core 3 O-glycosylation play critical roles in controlling Salmonella intestinal burdens and intestinal epithelial barrier function, respectively.

Gastrointestinal cell lines form polarized epithelia with an adherent mucus layer when cultured in semi-wet interfaces with mechanical stimulation

Mucin glycoproteins are secreted in large quantities by mucosal epithelia and cell surface mucins are a prominent feature of the glycocalyx of all mucosal epithelia. Currently, studies investigating the gastrointestinal mucosal barrier use either animal experiments or non-in vivo like cell cultures. Many pathogens cause different pathology in mice compared to humans and the in vitro cell cultures used are suboptimal because they are very different from an in vivo mucosal surface, are often not polarized, lack important components of the glycocalyx, and often lack the mucus layer. Although gastrointestinal cell lines exist that produce mucins or polarize, human cell line models that reproducibly create the combination of a polarized epithelial cell layer, functional tight junctions and an adherent mucus layer have been missing until now. We trialed a range of treatments to induce polarization, 3D-organization, tight junctions, mucin production, mucus secretion, and formation of an adherent mucus layer that can be carried out using standard equipment. These treatments were tested on cell lines of intestinal (Caco-2, LS513, HT29, T84, LS174T, HT29 MTX-P8 and HT29 MTX-E12) and gastric (MKN7, MKN45, AGS, NCI-N87 and its hTERT Clone5 and Clone6) origins using Ussing chamber methodology and (immuno)histology. Semi-wet interface culture in combination with mechanical stimulation and DAPT caused HT29 MTX-P8, HT29 MTX-E12 and LS513 cells to polarize, form functional tight junctions, a three-dimensional architecture resembling colonic crypts, and produce an adherent mucus layer. Caco-2 and T84 cells also polarized, formed functional tight junctions and produced a thin adherent mucus layer after this treatment, but with less consistency. In conclusion, culture methods affect cell lines differently, and testing a matrix of methods vs. cell lines may be important to develop better in vitro models. The methods developed herein create in vitro mucosal surfaces suitable for studies of host-pathogen interactions at the mucosal surface.

Comparison of the Caco-2, HT-29 and the mucus-secreting HT29-MTX intestinal cell models to investigate Salmonella adhesion and invasion

Human intestinal cell models are widely used to study host-enteric pathogen interactions, with different cell lines exhibiting specific characteristics and functions in the gut epithelium. In particular, the presence of mucus may play an important role in adhesion and invasion of pathogens. The aim of this study was to evaluate the suitability of the mucus-secreting HT29-MTX intestinal epithelial cell model to test adhesion and invasion of Salmonella strains and compare with data obtained with the more commonly used Caco-2 and HT-29 models. Adhesion of Salmonella to HT29-MTX cell model was significantly higher, likely due to high adhesiveness to mucins present in the native human mucus layer covering the whole cell surface, compared to the non- and low-mucus producing Caco-2 and HT-29 cell models, respectively. In addition, invasion percentages of some clinical Salmonella strains to HT29-MTX cultures were remarkably higher than to Caco-2 and HT-29 cells suggesting that these Salmonellae have subverted the mucus to enhance pathogenicity. The transepithelial electrical resistances of the infected HT29-MTX cell model decreased broadly and were highly correlated with invasion ability of the strain. Staining of S. Typhimurium-infected cell epithelium confirmed the higher invasion by Salmonella and subsequent disruption of tight junctions of HT29-MTX cell model compared with the Caco-2 and HT-29 cell models. Data from this study suggest that the HT29-MTX cell model, with more physiologically relevant characteristics with the mucus layer formation, could be better suited for studying cells-pathogens interactions.

Divergent mechanisms of interaction of Helicobacter pylori and Campylobacter jejuni with mucus and mucins

Helicobacter pylori and Campylobacter jejuni colonize the stomach and intestinal mucus, respectively. Using a combination of mucus-secreting cells, purified mucins, and a novel mucin microarray platform, we examined the interactions of these two organisms with mucus and mucins. H. pylori and C. jejuni bound to distinctly different mucins. C. jejuni displayed a striking tropism for chicken gastrointestinal mucins compared to mucins from other animals and preferentially bound mucins from specific avian intestinal sites (in order of descending preference: the large intestine, proximal small intestine, and cecum). H. pylori bound to a number of animal mucins, including porcine stomach mucin, but with less avidity than that of C. jejuni for chicken mucin. The strengths of interaction of various wild-type strains of H. pylori with different animal mucins were comparable, even though they did not all express the same adhesins. The production of mucus by HT29-MTX-E12 cells promoted higher levels of infection by C. jejuni and H. pylori than those for the non-mucus-producing parental cell lines. Both C. jejuni and H. pylori bound to HT29-MTX-E12 mucus, and while both organisms bound to glycosylated epitopes in the glycolipid fraction of the mucus, only C. jejuni bound to purified mucin. This study highlights the role of mucus in promoting bacterial infection and emphasizes the potential for even closely related bacteria to interact with mucus in different ways to establish successful infections.

In vitro characterization of aggregation and adhesion properties of viable and heat-killed forms of two probiotic Lactobacillus strains and interaction with foodborne zoonotic bacteria, especially Campylobacter jejuni

Bacterial aggregation and/or adhesion are key factors for colonization of the digestive ecosystem and the ability of probiotic strains to exclude pathogens. In the present study, two probiotic strains, Lactobacillus rhamnosus CNCM-I-3698 and Lactobacillus farciminis CNCM-I-3699, were evaluated as viable or heat-killed forms and compared with probiotic reference Lactobacillus strains (Lb. rhamnosus GG and Lb. farciminis CIP 103136). The autoaggregation potential of both forms was higher than that of reference strains and twice that of pathogenic strains. The coaggregation potential of these two beneficial micro-organisms was evaluated against several pathogenic agents that threaten the global safety of the feed/food chain: Escherichia coli, Salmonella spp., Campylobacter spp. and Listeria monocytogenes. The strongest coaggregative interactions were demonstrated with Campylobacter spp. by a coaggregation test, confirmed by electron microscopic examination for the two forms. Viable forms were investigated for the nature of the bacterial cell-surface molecules involved, by sugar reversal tests and chemical and enzymic pretreatments. The results suggest that the coaggregation between both probiotic strains and C. jejuni CIP 70.2(T) is mediated by a carbohydrate-lectin interaction. The autoaggregation potential of the two probiotics decreased upon exposure to proteinase, SDS or LiCl, showing that proteinaceous components on the surface of the two lactobacilli play an important role in this interaction. Adhesion abilities of both Lactobacillus strains were also demonstrated at significant levels on Caco-2 cells, mucin and extracellular matrix material. Both viable and heat-killed forms of the two probiotic lactobacilli inhibited the attachment of C. jejuni CIP 70.2(T) to mucin. In conclusion, in vitro assays showed that Lb. rhamnosus CNCM-I-3698 and Lb. farciminis CNCM-I-3699, as viable or heat-killed forms, are adherent to different intestinal matrix models and are highly aggregative in vitro with pathogens, especially Campylobacter spp., the most commonly reported zoonotic agent in the European Union. This study supports the need for further in vivo investigations to demonstrate the potential food safety benefits of Lb. rhamnosus CNCM-I-3698 and Lb. farciminis CNCM-I-3699, live or heat-killed, in the global feed/food chain.

Charles JL, Buffa BA, Brooks AP, Poe SA, Eaton KA, Stanhope MJ, Mansfield LS. Outcome of infection of C57BL/6 IL-10(-/-) mice with Campylobacter jejuni strains is correlated with genome content of open reading frames up- and down-regulated in vivo

Human Campylobacter jejuni infection can result in an asymptomatic carrier state, watery or bloody diarrhea, bacteremia, meningitis, or autoimmune neurological sequelae. Infection outcomes of C57BL/6 IL-10(-/-) mice orally infected with twenty-two phylogenetically diverse C. jejuni strains were evaluated to correlate colonization and disease phenotypes with genetic composition of the strains. Variation between strains was observed in colonization, timing of development of clinical signs, and occurrence of enteric lesions. Five pathotypes of C. jejuni in C57BL/6 IL-10(-/-) mice were delineated: little or no colonization, colonization without disease, colonization with enteritis, colonization with hemorrhagic enteritis, and colonization with neurological signs with or without enteritis. Virulence gene content of ten sequenced strains was compared in silico; virulence gene content of twelve additional strains was compared using a C. jejuni pan-genome microarray. Neither total nor virulence gene content predicted pathotype; nor was pathotype correlated with multilocus sequence type. Each strain was unique with regard to absences of known virulence-related loci and/or possession of point mutations and indels, including phase variation, in virulence-related genes. An experiment in C. jejuni 11168-infected germ-free mice showed that expression levels of ninety open reading frames (ORFs) were significantly up- or down-regulated in the mouse cecum at least two-fold compared to in vitro growth. Genomic content of these ninety C. jejuni 11168 ORFs was significantly correlated with the capacity to colonize and cause enteritis in C57BL/6 IL-10(-/-) mice. Differences in gene expression levels and patterns are thus an important determinant of pathotype in C. jejuni strains in this mouse model.

Investigation of motility and biofilm formation by intestinal Campylobacter concisus strains

Motility helps many pathogens swim through the highly viscous intestinal mucus. Given the differing outcomes of Campylobacter concisus infection, the motility of eight C. concisus strains isolated from patients with Crohn's disease (n=3), acute (n=3) and chronic (n=1) gastroenteritis and a healthy control (n=1) were compared. Following growth on solid or liquid media the eight strains formed two groups; however, the type of growth medium did not affect motility. In contrast, following growth in viscous liquid medium seven of the eight strains demonstrated significantly decreased motility. In media of increasing viscosities the motility of C. concisus UNSWCD had two marked increases at viscosities of 20.0 and 74.7 centipoises. Determination of the ability of UNSWCD to swim through a viscous medium, adhere to and invade intestinal epithelial cells showed that while adherence levels significantly decreased with increasing viscosity, invasion levels did not significantly change. In contrast, adherence to and invasion of UNSWCD to mucus-producing intestinal cells increased upon accumulation of mucus, as did bacterial aggregation. Given this aggregation, we determined the ability of the eight C. concisus strains to form biofilms, and showed that all strains formed biofilms. In conclusion, the finding that C. concisus strains could be differentiated into two groups based on their motility may suggest that strains with high motility have an increased ability to swim through the intestinal mucus and reach the epithelial layer.

Campylobacter jejuni induces extra-intestinal immune responses via Toll-like-receptor-4 signaling in conventional IL-10 deficient mice with chronic colitis

Campylobacter jejuni is one of the predominant causes for foodborne bacterial infections worldwide. We investigated whether signaling of C. jejuni-lipoproteins and -lipooligosaccharide via Toll-like-receptor (TLR) -2 and -4, respectively, is inducing intestinal and extra-intestinal immune responses following infection of conventional IL-10(-/-) mice with chronic colitis. At day 3 following oral infection, IL-10(-/-) mice lacking TLR-2 or TLR-4 harbored comparable C. jejuni strain ATCC 43431 loads in their colon. Interestingly, infected TLR-4(-/-) IL-10(-/-) mice displayed less compromized epithelial barrier function as indicated by lower translocation rates of live gut commensals into mesenteric lymphnodes (MLNs), and exhibited less distinct B lymphocyte responses in their colonic mucosa as compared to naїve IL-10(-/-) controls. Furthermore, in extra-intestinal compartments such as MLNs and spleens, abundance of myeloid cells was less distinct whereas relative percentages of activated T helper cells and cytotoxic T cells were higher in spleens and dendritic cells more abundant in MLNs of infected IL-10(-/-) animals lacking TLR-4 as compared to IL-10(-/-) controls. Taken together, in conventionally colonized IL-10(-/-) mice, TLR-4, but not TLR-2, is involved in mediating extra-intestinal pro-inflammatory immune responses following C. jejuni infection. Thus, conventional IL-10(-/-) mice are well suited to further dissect mechanisms underlying Campylobacter infections in vivo.

Repression of flagella motility in enterohemorrhagic Escherichia coli O157:H7 by mucin components

Whole genome-scale transcriptome analysis of enterohemorrhagic Escherichia coli (EHEC) O157:H7 EDL933 was performed to investigate the influence of mucin components on the EHEC gene expression. Here we report that the 732 candidate genes were differentially expressed by the presence of 0.5% porcine stomach mucin, including the 8 flagella-related genes. Quantitative real-time PCR analyses revealed that the transcription expression of the flg genes (encoding the structural components for flagella basal body) was down-regulated by the mucin components. Indeed, bacterial swarming motility was drastically reduced when grown on 0.3% trypton agar plates containing the mucin. These results imply that gastrointestinal (GI) mucin is a possible environmental signal which negatively regulates the flagellation of EHEC O157:H7 in the GI tract.

Human gastric mucins differently regulate Helicobacter pylori proliferation, gene expression and interactions with host cells

Helicobacter pylori colonizes the mucus niche of the gastric mucosa and is a risk factor for gastritis, ulcers and cancer. The main components of the mucus layer are heavily glycosylated mucins, to which H. pylori can adhere. Mucin glycosylation differs between individuals and changes during disease. Here we have examined the H. pylori response to purified mucins from a range of tumor and normal human gastric tissue samples. Our results demonstrate that mucins from different individuals differ in how they modulate both proliferation and gene expression of H. pylori. The mucin effect on proliferation varied significantly between samples, and ranged from stimulatory to inhibitory, depending on the type of mucins and the ability of the mucins to bind to H. pylori. Tumor-derived mucins and mucins from the surface mucosa had potential to stimulate proliferation, while gland-derived mucins tended to inhibit proliferation and mucins from healthy uninfected individuals showed little effect. Artificial glycoconjugates containing H. pylori ligands also modulated H. pylori proliferation, albeit to a lesser degree than human mucins. Expression of genes important for the pathogenicity of H. pylori (babA, sabA, cagA, flaA and ureA) appeared co-regulated in response to mucins. The addition of mucins to co-cultures of H. pylori and gastric epithelial cells protected the viability of the cells and modulated the cytokine production in a manner that differed between individuals, was partially dependent of adhesion of H. pylori to the gastric cells, but also revealed that other mucin factors in addition to adhesion are important for H. pylori-induced host signaling. The combined data reveal host-specific effects on proliferation, gene expression and virulence of H. pylori due to the gastric mucin environment, demonstrating a dynamic interplay between the bacterium and its host.

Host epithelial cell invasion by Campylobacter jejuni: trigger or zipper mechanism?

Campylobacter jejuni, a spiral-shaped Gram-negative pathogen, is a highly frequent cause of gastrointestinal foodborne illness in humans worldwide. Clinical outcome of C. jejuni infections ranges from mild to severe diarrheal disease, and some other complications including reactive arthritis and Guillain–Barré syndrome. This review article highlights various C. jejuni pathogenicity factors, host cell determinants, and proposed signaling mechanisms involved in human host cell invasion and their potential role in the development of C. jejuni-mediated disease. A model is presented which outlines the various important interactions of C. jejuni with the intestinal epithelium, and we discuss the pro’s and con’s for the “zipper” over the “trigger” mechanism of invasion. Future work should clarify the contradictory role of some previously identified factors, and should identify and characterize novel virulence determinants, which are crucial to provide fresh insights into the diversity of strategies employed by this pathogen to cause disease.

Defense and adaptation: the complex inter-relationship between Campylobacter jejuni and mucus

Mucus colonization is an essential early step toward establishing successful infection and disease by mucosal pathogens. There is an emerging literature implicating specific mucin sub-types and mucin modifications in protecting the host from Campylobacter jejuni infection. However, mucosal pathogens have evolved sophisticated mechanisms to breach the mucus layer and C. jejuni in particular appears to harbor specific adaptations to better colonize intestinal mucus. For example, components of mucus are chemotactic for C. jejuni and the rheological properties of mucus promote motility of the organism. Furthermore, recent studies demonstrate that mucins modulate the pathogenicity of C. jejuni in a species-specific manner and likely help determine whether these bacteria become pathogenic (as in humans), or adopt a commensal mode of existence (as in chickens and other animals). This review focuses on recent advances in understanding the complex interplay between C. jejuni and components of the mucus layer.

Glycoconjugates play a key role in Campylobacter jejuni Infection: interactions between host and pathogen

Glycan based interactions between host and pathogen are critical in many bacterial and viral diseases. Glycan interactions range from initial receptor based adherence to protecting the infective agent from the host’s immune response through molecular mimicry. Campylobacter jejuni is an ideal model for studying the role of glycans in host–pathogen interactions, as well as the role of bacterial surface glycoconjugates in infection. Using glycan array analysis, C. jejuni has been shown to interact with a wide range of host glycoconjugates. Mannose and sialic acid residues appear to play a role in initial interactions between host and pathogen following environmental exposure, whereas fucose and galactose based interactions are likely to be required for prolonged colonization. Other studies have highlighted potential decoy receptor type interactions between host’s intestinal mucins and C. jejuni, demonstrating the importance of host glycoproteins as defense against C. jejuni infection as well as the role for glycoconjugates found in human breast milk in protection of breast feeding infants from infection with C. jejuni. C. jejuni can produce N- and O-linked glycoproteins, capsular polysaccharide (CPS) and/or lipooligosaccharide (LOS) which results in C. jejuni presenting its own diverse sugar coated displays on the cell surface. Bacterial glycans play an important and versatile role in infection and disease. Of these, the best understood is the molecular mimicry of human gangliosides presented by C. jejuni’s LOS and its link to the onset of autoimmune neuropathies such as the Guillain Barrè syndrome (GBS). However, the role of glycoconjugates presented by C. jejuni extends beyond expression of sialylated ganglioside structures involved in initiation of GBS. Expression of surface glycans by C. jejuni may also relate to the ability of this organism to interact with the glycoproteins for initial host–pathogen interactions and continued infectivity.

Bacteria and host interactions in the gut epithelial barrier

The gut mucosa acts as a barrier against microbial invaders, whereas resident commensal and foreign invading bacteria interact intimately with the gut epithelium and influence the host cellular and immune systems. The epithelial barrier serves as an infectious foothold for many bacterial pathogens and as an entry port for pathogens to disseminate into deeper tissues. Enteric bacterial pathogens can efficiently infect the gut mucosa using highly sophisticated virulence mechanisms that allow bacteria to circumvent the defense barriers in the gut. We provide an overview of the components of the mucosal barrier and discuss the bacterial stratagems that circumvent these barriers with particular emphasis on the roles of bacterial effector proteins.

Microbial adhesins to gastrointestinal mucus

The gastrointestinal tract (GIT) is lined by a layer of mucus formed by mucin glycoproteins. This layer constitutes a physical and chemical barrier between the intestinal contents and the underlying epithelia. In addition to this protective role, mucins harbor glycan-rich domains that provide preferential binding sites for pathogens and commensal bacteria. Although mucus-microbial interactions in the GIT play a crucial role in determining the outcome of relationships of both commensal and pathogens with the host, the adhesins and ligands involved in the interaction are poorly delineated. This review focuses on the current knowledge of microbial adhesins to gastrointestinal mucus and mucus components.

A tolerogenic mucosal immune response leads to persistent Campylobacter jejuni colonization in the chicken gut

Campylobacter enteritis is the most reported zoonotic disease in many developed countries where it imposes a serious health burden. Campylobacter transmission to humans occurs primarily through the chicken vector. Chicks are regarded as a natural host for Campylobacter species and are colonized with C. jejuni in particular. But despite carrying a very high bacterial load in their gastrointestinal tract, these birds, in contrast to humans, do not develop pathological signs. It seems that in chickens C. jejuni principally harbors in the cecal mucosal crypts, where an inefficient inflammatory response fails to clear the bacterium from the gut. Recent intensive research resulted in an increased insight into the cross talk between C. jejuni and its avian host. This review discusses the chicken intestinal mucosal immune response upon C. jejuni entrance, leading to tolerance and persistent cecal colonization. It might in addition provide a solid base for further research regarding this topic aiming to fully understand the host-bacterium dynamics of C. jejuni in chicks and to develop effective control measures to clear this zoonotic pathogen from poultry lines.

Muc17 protects intestinal epithelial cells from enteroinvasive E. coli infection by promoting epithelial barrier integrity

The membrane-bound mucin MUC17 (mouse homolog Muc3) is highly expressed on the apical surface of intestinal epithelia and is thought to play a role in epithelial restitution and protection. Therefore, we hypothesized that MUC17 has a role in protection of the intestinal mucosa against luminal pathogens. Human intestinal cell lines were transfected by electroporation (Caco-2 and HT 29/19A) and by retroviral expression vector (LS174T, a cell line with high levels of MUC17 expression) using MUC17 siRNA. Transepithelial electrical resistance, permeability, tight-junction protein expression, adhesion, and invasion in response to enteroinvasive Escherichia coli (EIEC) were measured in all cell lines. In some experiments, the effect of the addition of exogenous purified crude mucin or recombinant Muc3 cysteine-rich domain protein (Muc3 CRD1-L-CRD2) as preventative or protective treatment was tested. Reduction of endogenous MUC17 is associated with increased permeability, inducible nitric oxide synthase and cyclooxygenase 2 induction, and enhanced bacterial invasion in response to EIEC exposure. Bacterial adhesion is not affected. Exogenous mucin (Muc3) and recombinant Muc3CRD treatment had a small but significant effect in attenuating the effects of EIEC infection. In conclusion, these data suggest that both native and exogenous MUC17 play a role in attachment and invasion of EIEC in colonic cell lines and in maintaining epithelial barrier function.

Mucin dynamics and enteric pathogens

The extracellular secreted mucus and the cell surface glycocalyx prevent infection by the vast numbers of microorganisms that live in the healthy gut. Mucin glycoproteins are the major component of these barriers. In this Review, we describe the components of the secreted and cell surface mucosal barriers and the evidence that they form an effective barricade against potential pathogens. However, successful enteric pathogens have evolved strategies to circumvent these barriers. We discuss the interactions between enteric pathogens and mucins, and the mechanisms that these pathogens use to disrupt and avoid mucosal barriers. In addition, we describe dynamic alterations in the mucin barrier that are driven by host innate and adaptive immune responses to infection.

Strain-dependent proliferation in response to human gastric mucin and adhesion properties of Helicobacter pylori are not affected by co-isolated Lactobacillus sp

BACKGROUND

Helicobacter pylori colonize the mucus layer that covers the gastric epithelium and can cause gastritis, ulcers, and gastric cancer. Recently, Lactobacillus sp. have also been found to reside in this niche permanently. This study compares adhesive properties and proliferation of co-isolated lactobacilli and H. pylori in the presence of mucins and investigates possibilities for lactobacilli-mediated inhibition of H. pylori.

MATERIALS AND METHODS

Binding and proliferation of four H. pylori and four Lactobacillus strains, simultaneously isolated after residing in the stomachs of four patients for >4 years, to human gastric mucins were investigated using microtiter-based methods.

RESULTS

The H. pylori strains co-isolated with lactobacilli exhibited the same mucin binding properties as demonstrated for H. pylori strains previously. In contrast, no binding to mucins was detected with the Lactobacillus strains. Proliferation of mucin-binding H. pylori strains was stimulated by the presence of mucins, whereas proliferation of non-binding H. pylori and Lactobacillus strains was unaffected. Associative cultures of co-isolated H. pylori and Lactobacillus strains showed no inhibition of H. pylori proliferation because of the presence of whole bacteria or supernatant of lactobacilli.

CONCLUSIONS

The presence of lactobacilli in the stomach did not select for different mucin binding properties of H. pylori, and Lactobacillus sp. did neither compete for binding sites nor inhibit the growth of co-isolated H. pylori. The effects of human gastric mucins on H. pylori proliferation vary between strains, and the host-bacteria interaction in the mucus niche thus depends on both the H. pylori strain and the microenvironment provided by the host mucins.

Changes in the mucosal barrier during acute and chronic Trichuris muris infection

The intestinal mucosal barrier, part of the innate immune defence, is responsive to the external environment and changes in response to infection. There is disparate evidence for the epithelial and goblet cell products within the intrinsic barrier being part of a response to resolve infection. We comprehensively analysed the changes of mucosal glycoconjugates during acute and chronic infection by utilising the Trichuris muris (T. muris) model. Transcription factors, atonal homolog 1 (Math-1) and SAM pointed domain containing ETS transcription factor (Spdef) were activated during acute infection, which promoted stem cell fate towards a secretory cell phenotype. The thickness of the intermediate barrier, the carbohydrate-rich glycocalyx, composed of cell surface mucins increased with exposure to T. muris, with an increase in Muc4, Muc13 and Muc17. Overall, hypersecretion of glycoproteins into the extrinsic barrier (mediated by IL-13) via the gamma amino-butyric acid-α3 receptor (GABA-α3), was observed during acute infection. Furthermore, altered glycosylation was observed during acute and chronic infection; mucins were more highly charged during acute infection than during chronic infection. This study readdresses the changes within the mucosal barrier, in particular in the cell surface and secreted mucins during acute and chronic nematode infection.

Phenotypic and genotypic evidence for L-fucose utilization by Campylobacter jejuni

Campylobacter jejuni remains among the leading causes of bacterial food-borne illness. The current understanding of Campylobacter physiology suggests that it is asaccharolytic and is unable to catabolize exogenous carbohydrates. Contrary to this paradigm, we provide evidence for l-fucose utilization by C. jejuni. The fucose phenotype, shown in chemically defined medium, is strain specific and linked to an 11-open reading frame (ORF) plasticity region of the bacterial chromosome. By constructing a mutation in fucP (encoding a putative fucose permease), one of the genes in the plasticity region, we found that this locus is required for fucose utilization. Consistent with their function in fucose utilization, transcription of the genes in the locus is highly inducible by fucose. PCR screening revealed a broad distribution of this genetic locus in strains derived from various host species, and the presence of this locus was consistently associated with fucose utilization. Birds inoculated with the fucP mutant strain alone were colonized at a level comparable to that by the wild-type strain; however, in cocolonization experiments, the mutant was significantly outcompeted by the wild-type strain when birds were inoculated with a low dose (10⁵ CFU per bird). This advantage was not observed when birds were inoculated at a higher inoculum dose (10⁸ CFU per bird). These results demonstrated a previously undescribed substrate that supports growth of C. jejuni and identified the genetic locus associated with the utilization of this substrate. These findings substantially enhance our understanding of the metabolic repertoire of C. jejuni and the role of metabolic diversity in Campylobacter pathobiology.

Enhancement of viable Campylobacter detection by chemotactic stimuli

The effects of chemotactic stimuli on motility ability of viable Campylobacter to pass through a 0.45 microm pore size filter in viscous condition were investigated. Reference strains including C. jejuni ATCC 33291, C. coli MUMT 18407, C. lari ATCC 43675, and C. upsaliensis DMST 19055 were used. The initial numbers of artificially-inoculated viable cells per g of chicken meat were approximately 10 to 10(4). Constituents of mucin plus bile (1:1), varieties of amino acids, and sodium salts were added into a soft-agar-coated membrane filter and incubated at both 37 degrees C and 42 degrees C for 24h. The drop plate method was used to determine numbers of viable Campylobacter at 6, 12, 18, and 24h. After 6h, constituents of mucin plus bile at the concentrations of 1, 5, and 10% demonstrated significant increases in numbers of viable cells (p<0.05). The numbers of the organisms at 42 degrees C were higher than those at 37 degrees C. In contrast, no significant difference in cell numbers was observed by adding amino acids or sodium salts. In addition, the role of starvation on chemotactic responses was also studied. Starved cells showed lower chemotactic response than non-starved cells. This method permitted rapid detection of viable thermophilic Campylobacter.

Probiotic colonization of the adherent mucus layer of HT29MTXE12 cells attenuates Campylobacter jejuni virulence properties

The HT29MTXE12 (E12) cell line harbors an adherent mucus layer, providing a novel technique to model mucosal infection in vitro. In this study, we have characterized the interaction of Campylobacter jejuni with the E12 cell line and exploited its unique mucus layer to examine the potential efficacy of probiotic treatment to attenuate C. jejuni virulence properties. C. jejuni 81-176 colonized and reproduced in E12 mucus. Adhesion to and internalization of C. jejuni were enhanced in E12 cells harboring mucus compared to parental cells without mucus. Translocation of C. jejuni occurred at early time points following infection. C. jejuni aligned with tight junctions and colocalized with the tight junction protein occludin, suggesting a paracellular route of translocation. Probiotic strains Lactobacillus rhamnosus R0011, Lactobacillus helveticus R0052, Lactobacillus salivarius AH102, Bifidobacterium longum AH1205, a commercial combination of L. rhamnosus R0011 and L. helveticus R0052 (Lacidofil), and a cocktail consisting of L. rhamnosus, L. helveticus, and L. salivarius (RhHeSa) colonized E12 mucus and bound to underlying cells. Probiotics attenuated C. jejuni association with and internalization into E12 cells and translocation to the basolateral medium of transwells. Live bacteria and prolonged precolonization of E12 cells with probiotics were necessary for probiotic action. These results demonstrate the potential for E12 cells as a model of mucosal pathogenesis and provide a rationale for the further investigation of probiotics as prophylaxis against human campylobacteriosis.

Two atypical enteropathogenic Escherichia coli strains induce the production of secreted and membrane-bound mucins to benefit their own growth at the apical surface of human mucin-secreting intestinal HT29-MTX cells

In rabbit ligated ileal loops, two atypical enteropathogenic Escherichia coli (aEPEC) strains, 3991-1 and 0421-1, intimately associated with the cell membrane, forming the characteristic EPEC attachment and effacement lesion of the brush border, induced a mucous hypersecretion, whereas typical EPEC (tEPEC) strain E2348/69 did not. Using cultured human mucin-secreting intestinal HT29-MTX cells, we demonstrate that apically aEPEC infection is followed by increased production of secreted MUC2 and MUC5AC mucins and membrane-bound MUC3 and MUC4 mucins. The transcription of the MUC5AC and MUC4 genes was transiently upregulated after aEPEC infection. We provide evidence that the apically adhering aEPEC cells exploit the mucins' increased production since they grew in the presence of membrane-bound mucins, whereas tEPEC did not. The data described herein report a putative new virulence phenomenon in aEPEC.

Update on Campylobacter jejuni vaccine development for preventing human campylobacteriosis

Campylobacteriosis constitutes a serious medical and socioeconomic problem worldwide. Rapidly increasing antibiotic resistance of bacterial strains compels us to develop alternative therapeutic strategies and to search for efficient immunoprophylactic methods. The vast majority of Campylobacter infections in developed countries occur as sporadic cases, mainly caused by eating undercooked Campylobacter-contaminated poultry. The most efficient strategy of decreasing the number of human Campylobacter infections is by implementing protective vaccinations for humans and/or chickens. Despite more than 10 years of research, an effective anti-Campylobacter vaccine has not been developed. This review highlights our increasing knowledge of Campylobacter interaction with host cells and focuses on recently published data describing the efficacy of anti-Campylobacter vaccine prototypes.

Mucin dynamics in intestinal bacterial infection

BACKGROUND

Bacterial gastroenteritis causes morbidity and mortality in humans worldwide. Murine Citrobacter rodentium infection is a model for gastroenteritis caused by the human pathogens enteropathogenic Escherichia coli and enterohaemorrhagic E. coli. Mucin glycoproteins are the main component of the first barrier that bacteria encounter in the intestinal tract.

METHODOLOGY/PRINCIPAL FINDINGS

Using Immunohistochemistry, we investigated intestinal expression of mucins (Alcian blue/PAS, Muc1, Muc2, Muc4, Muc5AC, Muc13 and Muc3/17) in healthy and C. rodentium infected mice. The majority of the C. rodentium infected mice developed systemic infection and colitis in the mid and distal colon by day 12. C. rodentium bound to the major secreted mucin, Muc2, in vitro, and high numbers of bacteria were found in secreted MUC2 in infected animals in vivo, indicating that mucins may limit bacterial access to the epithelial surface. In the small intestine, caecum and proximal colon, the mucin expression was similar in infected and non-infected animals. In the distal colonic epithelium, all secreted and cell surface mucins decreased with the exception of the Muc1 cell surface mucin which increased after infection (p<0.05). Similarly, during human infection Salmonella St Paul, Campylobacter jejuni and Clostridium difficile induced MUC1 in the colon.

CONCLUSION

Major changes in both the cell-surface and secreted mucins occur in response to intestinal infection.