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

Genes involved in the adhesion and invasion of Arcobacter butzleri

Arcobacter butzleri is a foodborne pathogen that mainly causes enteritis in humans, but the number of cases of bacteraemia has increased in recent years. However, there is still limited knowledge on the pathogenic mechanisms of this bacterium. To investigate how A. butzleri causes disease, single knockout mutants were constructed in the cadF, ABU_RS00335, ciaB, and flaAB genes, which might be involved in adhesion and invasion properties. These mutants and the isogenic wild-type (WT) were then tested for their ability to adhere and invade human Caco-2 and HT29-MTX cells. The adhesion and invasion of A. butzleri RM4018 strain was also visualized by a Leica CTR 6500 confocal microscope. The adhesion and invasion abilities of mutants lacking the invasion antigen CiaB or a functional flagellum were lower than those of the WTs. However, the extent of the decrease varied depending on the strain and/or cell line. Mutants lacking the fibronectin (FN)-binding protein CadF consistently exhibited reduced abilities, while the inactivation of the other studied FN-binding protein, ABU_RS00335, led to a reduction in only one of the two strains tested. Therefore, the ciaB and flaAB genes appear to be important for A. butzleri adhesion and invasion properties, while cadF appears to be indispensable.

Interaction of Neisseria meningitidis carrier and disease isolates of MenB cc32 and MenW cc22 with epithelial cells of the nasopharyngeal barrier

Neisseria meningitidis (Nm, the meningococcus) is considered an asymptomatic colonizer of the upper respiratory tract and a transient member of its microbiome. It is assumed that the spread of N. meningitidis into the bloodstream occurs via transcytosis of the nasopharyngeal epithelial barrier without destroying the barrier layer. Here, we used Calu-3 respiratory epithelial cells that were grown under air-liquid-interface conditions to induce formation of pseudostratified layers and mucus production. The number of bacterial localizations in the outer mucus, as well as cellular adhesion, invasion and transmigration of different carrier and disease N. meningitidis isolates belonging to MenB:cc32 and MenW:cc22 lineages was assessed. In addition, the effect on barrier integrity and cytokine release was determined. Our findings showed that all strains tested resided primarily in the outer mucus layer after 24 h of infection (>80%). Nonetheless, both MenB:cc32 and MenW:cc22 carrier and disease isolates reached the surface of the epithelial cells and overcame the barrier. Interestingly, we observed a significant difference in the number of bacteria transmigrating the epithelial cell barrier, with the representative disease isolates being more efficient to transmigrate compared to carrier isolates. This could be attributed to the capacity of the disease isolates to invade, however could not be assigned to expression of the outer membrane protein Opc. Moreover, we found that the representative meningococcal isolates tested in this study did not damage the epithelial barrier, as shown by TEER measurement, FITC-dextran permeability assays, and expression of cell-junction components.

Native gastrointestinal mucus: Critical features and techniques for studying interactions with drugs, drug carriers, and bacteria

Gastrointestinal mucus plays essential roles in modulating interactions between intestinal lumen contents, including orally delivered drug carriers and the gut microbiome, and underlying epithelial and immune tissues and cells. This review is focused on the properties of and methods for studying native gastrointestinal mucus and its interactions with intestinal lumen contents, including drug delivery systems, drugs, and bacteria. The properties of gastrointestinal mucus important to consider in its analysis are first presented, followed by a discussion of different experimental setups used to study gastrointestinal mucus. Applications of native intestinal mucus are then described, including experimental methods used to study mucus as a barrier to drug delivery and interactions with intestinal lumen contents that impact barrier properties. Given the significance of the microbiota in health and disease, its impact on drug delivery and drug metabolism, and the use of probiotics and microbe-based delivery systems, analysis of interactions of bacteria with native intestinal mucus is then reviewed. Specifically, bacteria adhesion to, motility within, and degradation of mucus is discussed. Literature noted is focused largely on applications of native intestinal mucus models as opposed to isolated mucins or reconstituted mucin gels.

Campylobacter jejuni: targeting host cells, adhesion, invasion, and survival

Campylobacter jejuni, causing strong enteritis, is an unusual bacterium with numerous peculiarities. Chemotactically controlled motility in viscous milieu allows targeted navigation to intestinal mucus and colonization. By phase variation, quorum sensing, extensive O-and N-glycosylation and use of the flagellum as type-3-secretion system C. jejuni adapts effectively to environmental conditions. C. jejuni utilizes proteases to open cell-cell junctions and subsequently transmigrates paracellularly. Fibronectin at the basolateral side of polarized epithelial cells serves as binding site for adhesins CadF and FlpA, leading to intracellular signaling, which again triggers membrane ruffling and reduced host cell migration by focal adhesion. Cell contacts of C. jejuni results in its secretion of invasion antigens, which induce membrane ruffling by paxillin-independent pathway. In addition to fibronectin-binding proteins, other adhesins with other target structures and lectins and their corresponding sugar structures are involved in host-pathogen interaction. Invasion into the intestinal epithelial cell depends on host cell structures. Fibronectin, clathrin, and dynein influence cytoskeletal restructuring, endocytosis, and vesicular transport, through different mechanisms. C. jejuni can persist over a 72-h period in the cell. Campylobacter-containing vacuoles, avoid fusion with lysosomes and enter the perinuclear space via dynein, inducing signaling pathways. Secretion of cytolethal distending toxin directs the cell into programmed cell death, including the pyroptotic release of proinflammatory substances from the destroyed cell compartments. The immune system reacts with an inflammatory cascade by participation of numerous immune cells. The development of autoantibodies, directed not only against lipooligosaccharides, but also against endogenous gangliosides, triggers autoimmune diseases. Lesions of the epithelium result in loss of electrolytes, water, and blood, leading to diarrhea, which flushes out mucus containing C. jejuni. Together with the response of the immune system, this limits infection time. Based on the structural interactions between host cell and bacterium, the numerous virulence mechanisms, signaling, and effects that characterize the infection process of C. jejuni, a wide variety of targets for attenuation of the pathogen can be characterized. The review summarizes strategies of C. jejuni for host-pathogen interaction and should stimulate innovative research towards improved definition of targets for future drug development. KEY POINTS: • Bacterial adhesion of Campylobacter to host cells and invasion into host cells are strictly coordinated processes, which can serve as targets to prevent infection. • Reaction and signalling of host cell depend on the cell type. • Campylobacter virulence factors can be used as targets for development of antivirulence drug compounds.

Genomic Island-Encoded Histidine Kinase and Response Regulator Coordinate Mannose Utilization with Virulence in Enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) is a highly adaptive pathogen and has acquired diverse genetic elements, such as genomic islands and prophages, via horizontal gene transfer to promote fitness in vivo. Two-component signaling systems (TCSs) allow bacteria to sense, respond to, and adapt to various environments. This study identified a putative two-component signaling system composed of the histidine kinase EDL5436 (renamed LmvK) and the response regulator EDL5428 (renamed LmvR) in EHEC. lmvK and lmvR along with EDL5429 to EDL5434 (EDL5429-5434) between them constitute the OI167 genomic island and are highly associated with the EHEC pathotype. EDL5429-5434 encode transporters and metabolic enzymes that contribute to growth on mannose and are directly upregulated by LmvK/LmvR in the presence of mannose, as revealed by quantitative PCR (qPCR) and DNase I footprint assays. Moreover, LmvR directly activates the expression of the type III secretion system in response to mannose and promotes the formation of attaching and effacing lesions on HeLa cells. Using human colonoid and mouse infection models, we show that lmvK and lmvR contributed greatly to adherence and microcolony (MC) formation ex vivo and colonization in vivo. Finally, RNA sequencing and chromatin immunoprecipitation coupled with sequencing analyses identified additional direct targets of LmvR, most of which are involved in metabolism. Given that mannose is a mucus-derived sugar that induces virulence and is preferentially used by EHEC during infection, our data revealed a previously unknown mechanism by which EHEC recognizes the host metabolic landscape and regulates virulence expression accordingly. Our findings provide insights into how pathogenic bacteria evolve by acquiring genetic elements horizontally to adapt to host environments. IMPORTANCE The gastrointestinal tract represents a complex and challenging environment for enterohemorrhagic Escherichia coli (EHEC). However, EHEC is a highly adaptable pathogen, requiring only 10 to 100 CFUs to cause infection. This ability was achieved partially by acquiring mobile genetic elements, such as genomic islands, that promote overall fitness. Mannose is an intestinal mucus-derived sugar that stimulates virulence and is preferentially used by EHEC during infection. Here, we characterize the OI167 genomic island of EHEC, which encodes a novel two-component signaling system (TCS) and transporters and metabolic enzymes (EDL5429-5434) involved in mannose utilization. The TCS directly upregulates EDL5429-5434 and genes encoding the type III secretion system in the presence of mannose. Moreover, the TCS contributes greatly to EHEC virulence ex vivo and in vivo. Our data demonstrate an elegant example in which EHEC strains evolve by acquiring genetic elements horizontally to recognize the host metabolic landscape and regulate virulence expression accordingly, leading to successful infections.

Role of mucus-bacteria interactions in Enterotoxigenic Escherichia coli (ETEC) H10407 virulence and interplay with human microbiome

The intestinal mucus layer has a dual role in human health constituting a well-known microbial niche that supports gut microbiota maintenance but also acting as a physical barrier against enteric pathogens. Enterotoxigenic Escherichia coli (ETEC), the major agent responsible for traveler's diarrhea, is able to bind and degrade intestinal mucins, representing an important but understudied virulent trait of the pathogen. Using a set of complementary in vitro approaches simulating the human digestive environment, this study aimed to describe how the mucus microenvironment could shape different aspects of the human ETEC strain H10407 pathophysiology, namely its survival, adhesion, virulence gene expression, interleukin-8 induction and interactions with human fecal microbiota. Using the TNO gastrointestinal model (TIM-1) simulating the physicochemical conditions of the human upper gastrointestinal (GI) tract, we reported that mucus secretion and physical surface sustained ETEC survival, probably by helping it to face GI stresses. When integrating the host part in Caco2/HT29-MTX co-culture model, we demonstrated that mucus secreting-cells favored ETEC adhesion and virulence gene expression, but did not impede ETEC Interleukin-8 (IL-8) induction. Furthermore, we proved that mucosal surface did not favor ETEC colonization in a complex gut microbial background simulated in batch fecal experiments. However, the mucus-specific microbiota was widely modified upon the ETEC challenge suggesting its role in the pathogen infectious cycle. Using multi-targeted in vitro approaches, this study supports the major role played by mucus in ETEC pathophysiology, opening avenues in the design of new treatment strategies.

Luminal and mucosa-associated caecal microbiota of chickens after experimental Campylobacter jejuni infection in the absence of Campylobacter-specific phages of group II and III

Campylobacteriosis is still the most commonly reported zoonosis in the European Union causing gastrointestinal disease in humans. One of the most common sources for these food-borne infections is broiler meat. Interactions between Campylobacter (C.) jejuni and the intestinal microbiota might influence Campylobacter colonization in chickens. The aim of the present study was to gain further knowledge about exclusive interactions of the host microbiota with C. jejuni in Campylobacter-specific phage-free chickens under standardized conditions and special biosafety precautions.Therefore, 12 artificially infected (C. jejuni inoculum with a challenge dose of 7.64 log₁₀ c.f.u.) and 12 control chickens of the breed Ross 308 were kept under special biosafety measures in an animal facility. At day 42 of life, microbiota studies were performed on samples of caecal digesta and mucus. No Campylobacter-specific phages were detected by real-time PCR analysis of caecal digesta of control or artificially infected chickens. Amplification of the 16S rRNA gene was performed within the hypervariable region V4 and subsequently sequenced with Illumina MiSeq platform. R (version 4.0.2) was used to compare the microbiota between C. jejuni-negative and C. jejuni-positive chickens. The factor chickens' infection status contributed significantly to the differences in microbial composition of mucosal samples, explaining 10.6 % of the microbiota variation (P=0.007) and in digesta samples, explaining 9.69 % of the microbiota variation (P=0.015). The strongest difference between C. jejuni-non-infected and C. jejuni-infected birds was observed for the family Peptococcaceae whose presence in C. jejuni-infected birds could not be demonstrated. Further, several genera of the family Ruminococcaceae appeared to be depressed in its abundance due to Campylobacter infection. A negative correlation was found between Christensenellaceae R-7 group and Campylobacter in C. jejuni-colonised chickens, both genera potentially competing for substrate. This makes Christensenellaceae R-7 group highly interesting for further studies that aim to find control options for Campylobacter infections and assess the relevance of this finding for chicken health and Campylobacter colonization.

Mucosal Environment Induces Phage Susceptibility in Streptococcus mutans

Pathogenic bacteria are attracted toward mucosa, as it is their way of entry into the body. However, we know surprisingly little about the phage-bacterium interactions in the mucosal environment. Here, we explored the effect of the mucosal environment on growth characteristics and phage-bacterium interactions in Streptococcus mutans, a causative agent of dental caries. We found that although mucin supplementation increased bacterial growth and survival, it decreased S. mutans biofilm formation. More importantly, the presence of mucin had a significant effect on S. mutans phage susceptibility. In two experiments done in Brain Heart Infusion Broth, phage M102 replication was detected only with 0.2% mucin supplementation. In 0.1 × Tryptic Soy Broth, 0.5% mucin supplementation led to a 4-log increase in phage titers compared with the control. These results suggest that the mucosal environment can have a major role in the growth, phage sensitivity, and phage resistance of S. mutans, and underline the importance of understanding the effect of mucosal environment on phage-bacterium interactions.

Mucus interaction to improve gastrointestinal retention and pharmacokinetics of orally administered nano-drug delivery systems

Oral delivery of therapeutics is the preferred route of administration due to ease of administration which is associated with greater patient medication adherence. One major barrier to oral delivery and intestinal absorption is rapid clearance of the drug and the drug delivery system from the gastrointestinal (GI) tract. To address this issue, researchers have investigated using GI mucus to help maximize the pharmacokinetics of the therapeutic; while mucus can act as a barrier to effective oral delivery, it can also be used as an anchoring mechanism to improve intestinal residence. Nano-drug delivery systems that use materials which can interact with the mucus layers in the GI tract can enable longer residence time, improving the efficacy of oral drug delivery. This review examines the properties and function of mucus in the GI tract, as well as diseases that alter mucus. Three broad classes of mucus-interacting systems are discussed: mucoadhesive, mucus-penetrating, and mucolytic drug delivery systems. For each class of system, the basis for mucus interaction is presented, and examples of materials that inform the development of these systems are discussed and reviewed. Finally, a list of FDA-approved mucoadhesive, mucus-penetrating, and mucolytic drug delivery systems is reviewed. In summary, this review highlights the progress made in developing mucus-interacting systems, both at a research-scale and commercial-scale level, and describes the theoretical basis for each type of system.

Mucin induces CRISPR-Cas defense in an opportunistic pathogen

Parasitism by bacteriophages has led to the evolution of a variety of defense mechanisms in their host bacteria. However, it is unclear what factors lead to specific defenses being deployed upon phage infection. To explore this question, we co-evolved the bacterial fish pathogen Flavobacterium columnare and its virulent phage V156 in presence and absence of a eukaryotic host signal (mucin) for sixteen weeks. The presence of mucin leads to a dramatic increase in CRISPR spacer acquisition, especially in low nutrient conditions where over 60% of colonies obtain at least one new spacer. Additionally, we show that the presence of a competitor bacterium further increases CRISPR spacer acquisition in F. columnare. These results suggest that ecological factors are important in determining defense strategies against phages, and that the phage-bacterium interactions on mucosal surfaces may select for the diversification of bacterial immune systems.

It is unknown what circumstances promote particular bacterial defenses against bacterial viruses (phages). Almeida & Hoikkala et al. show that mucin, derived from mucus, greatly accelerates CRISPR-Cas defenses against phage in an opportunistic pathogen.

Mucin induces CRISPR-Cas defense in an opportunistic pathogen

Parasitism by bacteriophages has led to the evolution of a variety of defense mechanisms in their host bacteria. However, it is unclear what factors lead to specific defenses being deployed upon phage infection. To explore this question, we co-evolved the bacterial fish pathogen Flavobacterium columnare and its virulent phage V156 in presence and absence of a eukaryotic host signal (mucin) for sixteen weeks. The presence of mucin leads to a dramatic increase in CRISPR spacer acquisition, especially in low nutrient conditions where over 60% of colonies obtain at least one new spacer. Additionally, we show that the presence of a competitor bacterium further increases CRISPR spacer acquisition in F. columnare. These results suggest that ecological factors are important in determining defense strategies against phages, and that the phage-bacterium interactions on mucosal surfaces may select for the diversification of bacterial immune systems.

Mucus and Mucins: The Underappreciated Host Defence System

The mucosal surfaces that form the boundary between the external environment and the underlying tissue are protected by a mucus barrier. Mucin glycoproteins, both secreted and cell surface mucins, are the major components of the barrier. They can exclude pathogens and toxins while hosting the commensal bacteria. In this review, we highlight the dynamic function of the mucins and mucus during infection, how this mucosal barrier is regulated, and how pathogens have evolved mechanisms to evade this defence system.

From Static to Dynamic: A Review on the Role of Mucus Heterogeneity in Particle and Microbial Transport

Mucus layers (McLs) are on the front line of the human defense system that protect us from foreign abiotic/biotic particles (e.g., airborne virus SARS-CoV-2) and lubricates our organs. Recently, the impact of McLs on human health (e.g., nutrient absorption and drug delivery) and diseases (e.g., infections and cancers) has been studied extensively, yet their mechanisms are still not fully understood due to their high variety among organs and individuals. We characterize these variances as the heterogeneity of McLs, which lies in the thickness, composition, and physiology, making the systematic research on the roles of McLs in human health and diseases very challenging. To advance mucosal organoids and develop effective drug delivery systems, a comprehensive understanding of McLs' heterogeneity and how it impacts mucus physiology is urgently needed. When the role of airway mucus in the penetration and transmission of coronavirus (CoV) is considered, this understanding may also enable a better explanation and prediction of the CoV's behavior. Hence, in this Review, we summarize the variances of McLs among organs, health conditions, and experimental settings as well as recent advances in experimental measurements, data analysis, and model development for simulations.

The barrier and beyond: Roles of intestinal mucus and mucin-type O-glycosylation in resistance and tolerance defense strategies guiding host-microbe symbiosis

Over the past two decades, our appreciation of the gut mucus has moved from a static lubricant to a dynamic and essential component of the gut ecosystem that not only mediates the interface between host tissues and vast microbiota, but regulates how this ecosystem functions to promote mutualistic symbioses and protect from microbe-driven diseases. By delving into the complex chemistry and biology of the mucus, combined with innovative in vivo and ex vivo approaches, recent studies have revealed novel insights into the formation and function of the mucus system, the O-glycans that make up this system, and how they mediate two major host-defense strategies - resistance and tolerance - to reduce damage caused by indigenous microbes and opportunistic pathogens. This current review summarizes these findings by highlighting the emerging roles of mucus and mucin-type O-glycans in influencing host and microbial physiology with an emphasis on host defense strategies against bacteria in the gastrointestinal tract.

Wolf in Sheep's Clothing: Clostridioides difficile Biofilm as a Reservoir for Recurrent Infections

The microbiota inhabiting the intestinal tract provide several critical functions to its host. Microorganisms found at the mucosal layer form organized three-dimensional structures which are considered to be biofilms. Their development and functions are influenced by host factors, host-microbe interactions, and microbe-microbe interactions. These structures can dictate the health of their host by strengthening the natural defenses of the gut epithelium or cause disease by exacerbating underlying conditions. Biofilm communities can also block the establishment of pathogens and prevent infectious diseases. Although these biofilms are important for colonization resistance, new data provide evidence that gut biofilms can act as a reservoir for pathogens such as Clostridioides difficile. In this review, we will look at the biofilms of the intestinal tract, their contribution to health and disease, and the factors influencing their formation. We will then focus on the factors contributing to biofilm formation in C. difficile, how these biofilms are formed, and their properties. In the last section, we will look at how the gut microbiota and the gut biofilm influence C. difficile biofilm formation, persistence, and transmission.

Tripartite relationship between gut microbiota, intestinal mucus and dietary fibers: towards preventive strategies against enteric infections

The human gut is inhabited by a large variety of microorganims involved in many physiological processes and collectively referred as to gut microbiota. Disrupted microbiome has been associated with negative health outcomes and especially could promote the onset of enteric infections. To sustain their growth and persistence within the human digestive tract, gut microbes and enteric pathogens rely on two main polysaccharide compartments, namely dietary fibers and mucus carbohydrates. Several evidences suggest that the three-way relationship between gut microbiota, dietary fibers and mucus layer could unravel the capacity of enteric pathogens to colonise the human digestive tract and ultimately lead to infection. The review starts by shedding light on similarities and differences between dietary fibers and mucus carbohydrates structures and functions. Next, we provide an overview of the interactions of these two components with the third partner, namely, the gut microbiota, under health and disease situations. The review will then provide insights into the relevance of using dietary fibers interventions to prevent enteric infections with a focus on gut microbial imbalance and impaired-mucus integrity. Facing the numerous challenges in studying microbiota-pathogen-dietary fiber-mucus interactions, we lastly describe the characteristics and potentialities of currently available in vitro models of the human gut.

Colonization of Clostridium butyricum in Rats and Its Effect on Intestinal Microbial Composition

Gut microorganisms participate in many physiological processes. In particular, Clostridium butyricum can modulate gut microorganisms and treat diseases. The colonization and persistence of strains in the gut contribute to beneficial effects, and the colonization by C. butyricum in the gut is currently unknown. We investigated the total intestinal contents of C. butyricum at 12 h, 24 h, 48 h, and four and six days using real-time reverse transcription-PCR, after oral administration of C. butyricum to rats for seven consecutive days. We assessed the bacterial community structure using Illumina MiSeq sequencing. The results showed that C. butyricum was mainly colonized in the colon. The total content of C. butyricum in the gut increased significantly at 12 h after administration. Exogenous C. butyricum could still be detected in the gut six days after administration. Administration of C. butyricum significantly enhanced gut microbial diversity. The relative abundance of short-chain fatty acid-producing bacterial genera was shown to be higher than that of the control group, and treatment with C. butyricum elevated Firmicutes and diminished Bacteroidetes phyla compared with to the control group. These findings laid the foundation for the study of probiotic colonization capacity and the improvement of microflora for the prevention of gut diseases.

Mucin-Degrading Microbes Release Monosaccharides That Chemoattract Clostridioides difficile and Facilitate Colonization of the Human Intestinal Mucus Layer

It is widely accepted that the pathogen Clostridioides difficile exploits an intestinal environment with an altered microbiota, but the details of these microbe-microbe interactions are unclear. Adherence and colonization of mucus has been demonstrated for several enteric pathogens and it is possible that mucin-associated microbes may be working in concert with C. difficile. We showed that C. difficile ribotype-027 adheres to MUC2 glycans and using fecal bioreactors, we identified that C. difficile associates with several mucin-degrading microbes. C. difficile was found to chemotax toward intestinal mucus and its glycan components, demonstrating that C. difficile senses the mucus layer. Although C. difficile lacks the glycosyl hydrolases required to degrade mucin glycans, coculturing C. difficile with the mucin-degrading Akkermansia muciniphila, Bacteroides thetaiotaomicron, and Ruminococcus torques allowed C. difficile to grow in media that lacked glucose but contained purified MUC2. Collectively, these studies expand our knowledge on how intestinal microbes support C. difficile.

Gastrointestinal biofilms in health and disease

Microorganisms colonize various ecological niches in the human habitat, as they do in nature. Predominant forms of multicellular communities called biofilms colonize human tissue surfaces. The gastrointestinal tract is home to a profusion of microorganisms with intertwined, but not identical, lifestyles: as isolated planktonic cells, as biofilms and in biofilm-dispersed form. It is therefore of major importance in understanding homeostatic and altered host-microorganism interactions to consider not only the planktonic lifestyle, but also biofilms and biofilm-dispersed forms. In this Review, we discuss the natural organization of microorganisms at gastrointestinal surfaces, stratification of microbiota taxonomy, biogeographical localization and trans-kingdom interactions occurring within the biofilm habitat. We also discuss existing models used to study biofilms. We assess the contribution of the host-mucosa biofilm relationship to gut homeostasis and to diseases. In addition, we describe how host factors can shape the organization, structure and composition of mucosal biofilms, and how biofilms themselves are implicated in a variety of homeostatic and pathological processes in the gut. Future studies characterizing biofilm nature, physical properties, composition and intrinsic communication could shed new light on gut physiology and lead to potential novel therapeutic options for gastrointestinal diseases.

Microbe-Driven Genotoxicity in Gastrointestinal Carcinogenesis

The intestinal epithelium serves as a barrier to discriminate the outside from the inside and is in constant exchange with the luminal contents, including nutrients and the microbiota. Pathogens have evolved mechanisms to overcome the multiple ways of defense in the mucosa, while several members of the microbiota can exhibit pathogenic features once the healthy barrier integrity of the epithelium is disrupted. This not only leads to symptoms accompanying the acute infection but may also contribute to long-term injuries such as genomic instability, which is linked to mutations and cancer. While for Helicobacter pylori a link between infection and cancer is well established, many other bacteria and their virulence factors have only recently been linked to gastrointestinal malignancies through epidemiological as well as mechanistic studies. This review will focus on those pathogens and members of the microbiota that have been linked to genotoxicity in the context of gastric or colorectal cancer. We will address the mechanisms by which such bacteria establish contact with the gastrointestinal epithelium-either via an existing breach in the barrier or via their own virulence factors as well as the mechanisms by which they interfere with host genomic integrity.

Investigating the Role of Mucin as Frontline Defense of Mucosal Surfaces against Mycobacterium avium Subsp. hominissuis

Mycobacterium avium is a human and animal pathogen that infects the host through the mucosal surfaces. Past work has demonstrated that the bacterium can interact with both the respiratory and gastrointestinal tracts. Those surfaces in the body are covered by a bilayer of a glycoprotein, mucin, which works as a physical barrier and a gel which contains antibacterial and antivirus properties. This current work shows that different strains of M. avium, in contrast to Escherichia coli, Pseudomonas aeruginosa, and Listeria monocytogenes, are not able to bind to mucins, MUC2 and MUC5b, the main mucins in the gastrointestinal and respiratory tracts, respectively. The lack of binding is due to the characteristics of the cell wall and is impaired by altering lipids, proteins, or glycolipids. M. avium, in contrast to E. coli, interacts with epithelial cells equally in the presence or absence of the mucin, suggesting that the cell wall of the pathogen can facilitate the bacterial movement through the mucin layer, towards the mucosal wall. In conclusion, the study has shown that M. avium can avoid the mucin barrier, which explains its ability to interact with the mucosal epithelium, even in absence of motion-related structures.

Application of a gut-immune co-culture system for the study of N-glycan-dependent host-pathogen interactions of Campylobacter jejuni

An in vitro gut-immune co-culture model with apical and basal accessibility, designed to more closely resemble a human intestinal microenvironment, was employed to study the role of the N-linked protein glycosylation pathway in Campylobacter jejuni pathogenicity. The gut-immune co-culture (GIC) was developed to model important aspects of the human small intestine by the inclusion of mucin-producing goblet cells, human enterocytes and dendritic cells, bringing together a mucus-containing epithelial monolayer with elements of the innate immune system. The utility of the system was demonstrated by characterizing host-pathogen interactions facilitated by N-linked glycosylation, such as host epithelial barrier functions, bacterial invasion and immunogenicity. Changes in human intestinal barrier functions in the presence of 11168 C. jejuni (wildtype) strains were quantified using GICs. The glycosylation-impaired strain 11168 ΔpglE was 100-fold less capable of adhering to and invading this intestinal model in cell infectivity assays. Quantification of inflammatory signaling revealed that 11168ΔpglE differentially modulated inflammatory responses in different intestinal microenvironments, suppressive in some but activating in others. Virulence-associated outer membrane vesicles produced by wildtype and 11168ΔpglE C. jejuni were shown to have differential composition and function, with both leading to immune system activation when provided to the gut-immune co-culture model. This analysis of aspects of C. jejuni infectivity in the presence and absence of its N-linked glycome is enabled by application of the gut-immune model, and we anticipate that this system will be applicable to further studies of C. jejuni and other enteropathogens of interest.

Taking Control: Campylobacter jejuni Binding to Fibronectin Sets the Stage for Cellular Adherence and Invasion

Campylobacter jejuni, a foodborne pathogen, is one of the most common bacterial causes of gastroenteritis in the world. Undercooked poultry, raw (unpasteurized) dairy products, untreated water, and contaminated produce are the most common sources associated with infection. C. jejuni establishes a niche in the gut by adhering to and invading epithelial cells, which results in diarrhea with blood and mucus in the stool. The process of colonization is mediated, in part, by surface-exposed molecules (adhesins) that bind directly to host cell ligands or the extracellular matrix (ECM) surrounding cells. In this review, we introduce the known and putative adhesins of the foodborne pathogen C. jejuni. We then focus our discussion on two C. jejuni Microbial Surface Components Recognizing Adhesive Matrix Molecule(s) (MSCRAMMs), termed CadF and FlpA, which have been demonstrated to contribute to C. jejuni colonization and pathogenesis. In vitro studies have determined that these two surface-exposed proteins bind to the ECM glycoprotein fibronectin (FN). In vivo studies have shown that cadF and flpA mutants exhibit impaired colonization of chickens compared to the wild-type strain. Additional studies have revealed that CadF and FlpA stimulate epithelial cell signaling pathways necessary for cell invasion. Interestingly, CadF and FlpA have distinct FN-binding domains, suggesting that the functions of these proteins are non-redundant. In summary, the binding of FN by C. jejuni CadF and FlpA adhesins has been demonstrated to contribute to adherence, invasion, and cell signaling.

Human Immunity Against Campylobacter Infection

Campylobacter is a worldwide foodborne pathogen, associated with human gastroenteritis. The efficient translocation of Campylobacter and its ability to secrete toxins into host cells are the 2 key features of Campylobacter pathophysiology which trigger inflammation in intestinal cells and contribute to the development of gastrointestinal symptoms, particularly diarrhoea, in humans. The purpose of conducting this literature review is to summarise the current understanding of: i) the human immune responses involved in the elimination of Campylobacter infection and ii) the resistance potential in Campylobacter against these immune responses. This review has highlighted that the intestinal epithelial cells are the preliminary cells which sense Campylobacter cells by means of their cell-surface and cytosolic receptors, activate various receptors-dependent signalling pathways, and recruit the innate immune cells to the site of inflammation. The innate immune system, adaptive immune system, and networking between these systems play a crucial role in bacterial clearance. Different cellular constituents of Campylobacter, mainly cell membrane lipooligosaccharides, capsule, and toxins, provide protection to Campylobacter against the human immune system mediated killing. This review has also identified gaps in knowledge, which are related to the activation of following during Campylobacter infection: i) cathelicidins, bactericidal permeability-increasing proteins, chemokines, and inflammasomes in intestinal epithelial cells; ii) siglec-7 receptors in dendritic cell; iii) acute phase proteins in serum; and iv) T-cell subsets in lymphoid nodules. This review evaluates the existing literature to improve the understanding of human immunity against Campylobacter infection and identify some of the knowledge gaps for future research.

"Candida Albicans Interactions With The Host: Crossing The Intestinal Epithelial Barrier"

Formerly a commensal organism of the mucosal surfaces of most healthy individuals, Candida albicans is an opportunistic pathogen that causes infections ranging from superficial to the more life-threatening disseminated infections, especially in the ever-growing population of vulnerable patients in the hospital setting. In these situations, the fungus takes advantage of its host following a disturbance in the host defense system and/or the mucosal microbiota. Overwhelming evidence suggests that the gastrointestinal tract is the main source of disseminated C. albicans infections. Major risk factors for disseminated candidiasis include damage to the mucosal intestinal barrier, immune dysfunction, and dysbiosis of the resident microbiota. A better understanding of C. albicans' interaction with the intestinal epithelial barrier will be useful for designing future therapies to avoid systemic candidiasis. In this review, we provide an overview of the current knowledge regarding the mechanisms of pathogenicity that allow the fungus to reach and translocate the gut barrier.

Essential Oils as an Intervention Strategy to Reduce Campylobacter in Poultry Production: A Review

Campylobacter is a major foodborne pathogen and can be acquired through consumption of poultry products. With 1.3 million United States cases a year, the high prevalence of Campylobacter within the poultry gastrointestinal tract is a public health concern and thus a target for the development of intervention strategies. Increasing demand for antibiotic-free products has led to the promotion of various alternative pathogen control measures both at the farm and processing level. One such measure includes utilizing essential oils in both pre- and post-harvest settings. Essential oils are derived from plant-based extracts, and there are currently over 300 commercially available compounds. They have been proposed to control Campylobacter in the gastrointestinal tract of broilers. When used in concentrations low enough to not influence sensory characteristics, essential oils have also been proposed to decrease bacterial contamination of the poultry product during processing. This review explores the use of essential oils, particularly thymol, carvacrol, and cinnamaldehyde, and their role in reducing Campylobacter concentrations both pre- and post-harvest. This review also details the suggested mechanisms of action of essential oils on Campylobacter.

Porcine Gastric Mucin Triggers Toxin Production of Enteropathogenic Bacillus cereus

Enteropathogenic Bacillus cereus causes foodborne infections due to the production of pore-forming enterotoxins in the intestine. Before that, spores have to be ingested, survive the stomach passage, and germinate. Thus, before reaching epithelial cells, B. cereus comes in contact with the intestinal mucus layer. In the present study, different aspects of this interaction were analyzed. Total RNA sequencing revealed major transcriptional changes of B. cereus strain F837/76 upon incubation with porcine gastric mucin (PGM), comprising genes encoding enterotoxins and further putative virulence factors, as well as proteins involved in adhesion to and degradation of mucin. Indeed, PGM was partially degraded by B. cereus via secreted, EDTA-sensitive proteases. The amount of enterotoxins detectable in culture media supplemented with PGM was also clearly increased. Tests of further strains revealed that enhancement of enterotoxin production upon contact with PGM is broadly distributed among B. cereus strains. Interestingly, evidence was found that PGM can also strain-specifically trigger germination of B. cereus spores and that vegetative cells actively move toward mucin. Overall, our data suggest that B. cereus is well adapted to the host environment due to massive transcriptome changes upon contact with PGM, attributing mucin an important and, thus far, neglected role in pathogenesis.

Genomic correlates of extraintestinal infection are linked with changes in cell morphology in Campylobacter jejuni

Campylobacter jejuni is the most common cause of bacterial diarrheal disease in the world. Clinical outcomes of infection can range from asymptomatic infection to life-threatening extraintestinal infections. This variability in outcomes for infected patients has raised questions as to whether genetic differences between C. jejuni isolates contribute to their likelihood of causing severe disease. In this study, we compare the genomes of ten C. jejuni isolates that were implicated in extraintestinal infections with reference gastrointestinal isolates, in order to identify unusual patterns of sequence variation associated with infection outcome. We identified a collection of genes that display a higher burden of uncommon mutations in invasive isolates compared with gastrointestinal close relatives, including some that have been previously linked to virulence and invasiveness in C. jejuni. Among the top genes identified were mreB and pgp1, which are both involved in determining cell shape. Electron microscopy confirmed morphological differences in isolates carrying unusual sequence variants of these genes, indicating a possible relationship between extraintestinal infection and changes in cell morphology.

Intestinal Microbiota as a Host Defense Mechanism to Infectious Threats

The intestinal microbiota is a complex microbial community, with diverse and stable populations hosted by the gastrointestinal tract since birth. This ecosystem holds multiple anti-infectious, anti-inflammatory, and immune modulating roles decisive for intestinal homeostasis. Among these, colonization resistance refers to the dynamic antagonistic interactions between commensals and pathogenic flora. Hence, gut bacteria compete for the same intestinal niches and substrates, while also releasing antimicrobial substances such as bacteriocines and changing the environmental conditions. Short chain fatty acids (SCFAs) generated in anaerobic conditions prompt epigenetic regulatory mechanisms that favor a tolerogenic immune response. In addition, the commensal flora is involved in the synthesis of bactericidal products, namely secondary biliary acids or antimicrobial peptides (AMPs) such as cathellicidin-LL37, an immunomodulatory, antimicrobial, and wound healing peptide. Gut microbiota is protected through symbiotic relations with the hosting organism and by quorum sensing, a specific cell-to-cell communication system. Any alterations of these relationships favor the uncontrollable multiplication of the resident pathobionts or external entero-pathogens, prompting systemic translocations, inflammatory reactions, or exacerbations of bacterial virulence mechanisms (T6SS, T3SS) and ultimately lead to gastrointestinal or systemic infections. The article describes the metabolic and immunological mechanisms through which the intestinal microbiota is both an ally of the organism against enteric pathogens and an enemy that favors the development of infections.

Unexpected differential metabolic responses of Campylobacter jejuni to the abundant presence of glutamate and fucose

INTRODUCTION

Campylobacter jejuni is the leading cause of foodborne bacterial enteritis in humans, and yet little is known in regard to how genetic diversity and metabolic capabilities among isolates affect their metabolic phenotype and pathogenicity.

OBJECTIVES

For instance, the C. jejuni 11168 strain can utilize both L-fucose and L-glutamate as a carbon source, which provides the strain with a competitive advantage in some environments and in this study we set out to assess the metabolic response of C. jejuni 11168 to the presence of L-fucose and L-glutamate in the growth medium.

METHODS

To achieve this, untargeted hydrophilic liquid chromatography coupled to mass spectrometry was used to obtain metabolite profiles of supernatant extracts obtained at three different time points up to 24 h.

RESULTS

This study identified both the depletion and the production and subsequent release of a multitude of expected and unexpected metabolites during the growth of C. jejuni 11168 under three different conditions. A large set of standards allowed identification of a number of metabolites. Further mass spectrometry fragmentation analysis allowed the additional annotation of substrate-specific metabolites. The results show that C. jejuni 11168 upon L-fucose addition indeed produces degradation products of the fucose pathway. Furthermore, methionine was faster depleted from the medium, consistent with previously-observed methionine auxotrophy.

CONCLUSIONS

Moreover, a multitude of not previously annotated metabolites in C. jejuni were found to be increased specifically upon L-fucose addition. These metabolites may well play a role in the pathogenicity of this C. jejuni strain.

Capacity to adhere to and invade human epithelial cells, as related to the presence of virulence genes in, motility of, and biofilm formation of Campylobacter jejuni strains isolated from chicken and cattle

Campylobacter jejuni is a zoonotic pathogen transmitted through the "farm to fork" route. Outbreaks are generally associated with the consumption of chicken meat; however, dairy cows, birds, wild and domestic food animals, and pets are other important sources. Currently, there are not enough data comparing the virulence of strains isolated from these reservoirs. In this study, we compared C. jejuni strains isolated from broiler chickens and dairy cattle by determining their ability to adhere to and invade in vitro human colonic epithelial cells in the T84 cell line with their motility, formation of biofilms, and presence of eight virulence genes. A Wilcoxon Rank Sum test was performed to establish the relationship between presence of the studied genes and cellular invasion and adhesion, as well as differences between the animal species of origin of the isolate. A Spearman correlation was performed to assess the relationship between invasion and motility, along with invasion and biofilm generation. The virB11 gene was positively associated with the adherence capacity of the strains (mean difference = 0.21, p = 0.006), and strains isolated from chickens showed a significant difference for adherence compared with strains isolated from cattle (p = 0.0001). Our results indicate that strains of C. jejuni have a difference in their adherence capacity depending on the animal reservoir from which they came, with chicken isolates displaying higher virulence than dairy cattle isolates.

The Interaction of the Gut Microbiota with the Mucus Barrier in Health and Disease in Human

Glycoproteins are major players in the mucus protective barrier in the gastrointestinal and other mucosal surfaces. In particular the mucus glycoproteins, or mucins, are responsible for the protective gel barrier. They are characterized by their high carbohydrate content, present in their variable number, tandem repeat domains. Throughout evolution the mucins have been maintained as integral components of the mucosal barrier, emphasizing their essential biological status. The glycosylation of the mucins is achieved through a series of biosynthetic pathways processes, which generate the wide range of glycans found in these molecules. Thus mucins are decorated with molecules having information in the form of a glycocode. The enteric microbiota interacts with the mucosal mucus barrier in a variety of ways in order to fulfill its many normal processes. How bacteria read the glycocode and link to normal and pathological processes is outlined in the review.

Mucus-Pathogen Interactions in the Gastrointestinal Tract of Farmed Animals

Gastrointestinal infections cause significant challenges and economic losses in animal husbandry. As pathogens becoming resistant to antibiotics are a growing concern worldwide, alternative strategies to treat infections in farmed animals are necessary in order to decrease the risk to human health and increase animal health and productivity. Mucosal surfaces are the most common route used by pathogens to enter the body. The mucosal surface that lines the gastrointestinal tract is covered by a continuously secreted mucus layer that protects the epithelial surface. The mucus layer is the first barrier the pathogen must overcome for successful colonization, and is mainly composed of densely glycosylated proteins called mucins. The vast array of carbohydrate structures present on the mucins provide an important setting for host-pathogen interactions. This review summarizes the current knowledge on gastrointestinal mucins and their role during infections in farmed animals. We examine the interactions between mucins and animal pathogens, with a focus on how pathogenic bacteria can modify the mucin environment in the gut, and how this in turn affects pathogen adhesion and growth. Finally, we discuss analytical challenges and complexities of the mucus-based defense, as well as its potential to control infections in farmed animals.

Structural studies and molecular dynamics simulations suggest a processive mechanism of exolytic lytic transglycosylase from Campylobacter jejuni

The bacterial soluble lytic transglycosylase (LT) breaks down the peptidoglycan (PG) layer during processes such as cell division. We present here crystal structures of the soluble LT Cj0843 from Campylobacter jejuni with and without bulgecin A inhibitor in the active site. Cj0843 has a doughnut shape similar but not identical to that of E. coli SLT70. The C-terminal catalytic domain is preceded by an L-domain, a large helical U-domain, a flexible linker, and a small N-terminal NU-domain. The flexible linker allows the NU-domain to reach over and complete the circular shape, using residues conserved in the Epsilonproteobacteria LT family. The inner surface of the Cj0843 doughnut is mostly positively charged including a pocket that has 8 Arg/Lys residues. Molecular dynamics simulations with PG strands revealed a potential functional role for this pocket in anchoring the negatively charged terminal tetrapeptide of the PG during several steps in the reaction including homing and aligning the PG strand for exolytic cleavage, and subsequent ratcheting of the PG strand to enhance processivity in degrading PG strands.

Dynamics of metatranscription in the inflammatory bowel disease gut microbiome

Inflammatory bowel disease (IBD) is a group of chronic diseases of the digestive tract that affects millions of people worldwide. Genetic, environmental and microbial factors have been implicated in the onset and exacerbation of IBD. However, the mechanisms associating gut microbial dysbioses and aberrant immune responses remain largely unknown. The integrative Human Microbiome Project seeks to close these gaps by examining the dynamics of microbiome functionality in disease by profiling the gut microbiomes of >100 individuals sampled over a 1-year period. Here, we present the first results based on 78 paired faecal metagenomes and metatranscriptomes, and 222 additional metagenomes from 59 patients with Crohn's disease, 34 with ulcerative colitis and 24 non-IBD control patients. We demonstrate several cases in which measures of microbial gene expression in the inflamed gut can be informative relative to metagenomic profiles of functional potential. First, although many microbial organisms exhibited concordant DNA and RNA abundances, we also detected species-specific biases in transcriptional activity, revealing predominant transcription of pathways by individual microorganisms per host (for example, by Faecalibacterium prausnitzii). Thus, a loss of these organisms in disease may have more far-reaching consequences than suggested by their genomic abundances. Furthermore, we identified organisms that were metagenomically abundant but inactive or dormant in the gut with little or no expression (for example, Dialister invisus). Last, certain disease-specific microbial characteristics were more pronounced or only detectable at the transcript level, such as pathways that were predominantly expressed by different organisms in patients with IBD (for example, Bacteroides vulgatus and Alistipes putredinis). This provides potential insights into gut microbial pathway transcription that can vary over time, inducing phenotypical changes that are complementary to those linked to metagenomic abundances. The study's results highlight the strength of analysing both the activity and the presence of gut microorganisms to provide insight into the role of the microbiome in IBD.

Interactions of Intestinal Bacteria with Components of the Intestinal Mucus

The human gut is colonized by a variety of large amounts of microbes that are collectively called intestinal microbiota. Most of these microbial residents will grow within the mucus layer that overlies the gut epithelium and will act as the first line of defense against both commensal and invading microbes. This mucus is essentially formed by mucins, a family of highly glycosylated protein that are secreted by specialize cells in the gut. In this Review, we examine how commensal members of the microbiota and pathogenic bacteria use mucus to their advantage to promote their growth, develop biofilms and colonize the intestine. We also discuss how mucus-derived components act as nutrient and chemical cues for adaptation and pathogenesis of bacteria and how bacteria can influence the composition of the mucus layer.

Use of Recombinant Mucin Glycoprotein to Assess the Interaction of the Gastric Pathogen Helicobacter pylori with the Secreted Human Mucin MUC5AC

There is intense interest in how bacteria interact with mucin glycoproteins in order to colonise mucosal surfaces. In this study, we have assessed the feasibility of using recombinant mucin glycoproteins to study the interaction of the gastric pathogen Helicobacter pylori with MUC5AC, a mucin which the organism exhibits a distinct tropism for. Stable clonal populations of cells expressing a construct encoding for a truncated version of MUC5AC containing N- and C-termini interspersed with two native tandem repeat sequences (N + 2TR + C) were generated. Binding of H. pylori to protein immunoprecipitated from cell lysates and supernatants was assessed. High molecular weight mucin could be detected in both cell lysates and supernatants of transfected cells. Recombinant protein formed high molecular weight oligomers, was both N and O glycosylated, underwent cleavage similar to native MUC5AC and was secreted from the cell. H. pylori bound better to secreted mucin than intracellular mucin suggesting that modifications on extracellular MUC5AC promoted binding. Lectin analysis demonstrated that secreted mucin was differentially glycosylated compared to intracellular mucin. H. pylori also bound to a recombinant C-terminus MUC5AC protein, but binding to this protein did not inhibit binding to the N + 2TR + C protein. This study demonstrates the feasibility of using recombinant mucins containing tandem repeat sequences to assess microbial mucin interactions.

Motility of Campylobacter concisus isolated from saliva, feces, and gut mucosal biopsies

Campylobacter concisus is an emerging pathogen associated with gastrointestinal disorders such as gastroenteritis and inflammatory bowel diseases (IBD), but the species is also found in healthy subjects. The heterogeneous genome of C. concisus increases the likelihood of varying virulence between strains. Flagella motility is a crucial virulence factor for the well-recognized Campylobacter jejuni; therefore, this study aimed to analyze the motility of C. concisus isolated from saliva, gut biopsies, and feces of patients with IBD, gastroenteritis, and healthy subjects. The motility zones of 63 isolates from 52 patients were measured after microaerobic growth in soft-agar plates for 72 hours. The motility of C. concisus was significantly lower than that of Campylobacter jejuni and Campylobacter fetus subsp. fetus. The motility of C. concisus varied between isolates (4-22 mm), but there was no statistical significant difference between isolates from IBD patients and healthy subjects (p = 0.14). A tendency of a larger motility zones was observed for IBD gut mucosa isolates, although it did not reach statistical significance (p = 0.13), and no difference was found between oral or fecal isolates between groups. In conclusion, the varying motility of C. concisus could not be related to disease outcome or colonization sites.

Methods to Assess the Direct Interaction of C. jejuni with Mucins

Studies of the interaction of bacteria with mucus-secreting cells can be complemented at a more mechanistic level by exploring the interaction of bacteria with purified mucins. Here we describe a far Western blotting approach to show how C. jejuni proteins separated by SDS PAGE and transferred to a membrane or slot blotted directly onto a membrane can be probed using biotinylated mucin. In addition we describe the use of novel mucin microarrays to assess bacterial interactions with mucins in a high-throughput manner.

Ex Vivo and In Vivo Mice Models to Study Blastocystis spp. Adhesion, Colonization and Pathology: Closer to Proving Koch's Postulates

Blastocystis spp. are widely prevalent extra cellular, non-motile anerobic protists that inhabit the gastrointestinal tract. Although Blastocystis spp. have been associated with gastrointestinal symptoms, irritable bowel syndrome and urticaria, their clinical significance has remained controversial. We established an ex vivo mouse explant model to characterize adhesion in the context of tissue architecture and presence of the mucin layer. Using confocal microscopy with tissue whole mounts and two axenic isolates of Blastocystis spp., subtype 7 with notable differences in adhesion to intestinal epithelial cells (IEC), isolate B (ST7-B) and isolate H (more adhesive, ST7-H), we showed that adhesion is both isolate dependent and tissue trophic. The more adhesive isolate, ST7-H was found to bind preferentially to the colon tissue than caecum and terminal ileum. Both isolates were also found to have mucinolytic effects. We then adapted a DSS colitis mouse model as a susceptible model to study colonization and acute infection by intra-caecal inoculation of trophic Blastocystis spp.cells. We found that the more adhesive isolate ST7-H was also a better colonizer with more mice shedding parasites and for a longer duration than ST7-B. Adhesion and colonization was also associated with increased virulence as ST7-H infected mice showed greater tissue damage than ST7-B. Both the ex vivo and in vivo models used in this study showed that Blastocystis spp. remain luminal and predominantly associated with mucin. This was further confirmed using colonic loop experiments. We were also successfully able to re-infect a second batch of mice with ST7-H isolates obtained from fecal cultures and demonstrated similar histopathological findings and tissue damage thereby coming closer to proving Koch’s postulates for this parasite.

Piggyback-the-Winner in host-associated microbial communities

Phages can exploit their bacterial hosts by lytic infection, when many viral particles are released at cell lysis, or by lysogeny, when phages integrate into the host's genome. We recently proposed a new dynamic model of bacteria-phage interactions in which lysogeny predominates at high microbial abundance and growth rates. This model, named Piggyback-the-Winner (PtW), contrasts to current accepted models on the frequency of lysis and lysogeny and predicts that phages integrate into their hosts' genomes as prophages when microbial abundances and growth rates are high. According to PtW, switching to the temperate life cycle reduces phage predation control on bacterial abundance and confers superinfection exclusion, preventing that a closely-related phage infects the same bacterial cell. Here we examine how PtW is important for metazoans. Specifically, we postulate that PtW and the recently described bacteriophage adherence to mucus (BAM) model are strongly interrelated and have an important role in the development of the microbiome. In BAM, phage produced by the microbiome attach to mucins and protect underlying epithelial cells from invading bacteria. Spatial structuring of the mucus creates a gradient of phage replication strategies consistent with PtW. We predict that lysogeny is favored at the top mucosal layer and lytic predation predominates in the bacteria-sparse intermediary layers. The lysogeny confers competitive advantage to commensals against niche invasion and the lytic infection eliminates potential pathogens from deeper mucus layers.

Colonic Expression of Genes Encoding Inflammatory Mediators and Gelatinases During Campylobacter Jejuni Infection of Conventional Infant Mice

Within 1 week following peroral Campylobacter jejuni infection, infant mice develop acute enteritis resolving thereafter. We here assessed colonic expression profiles of mediators belonging to the IL-23/IL-22/IL-18 axis and of matrix-degrading gelatinases MMP-2 and MMP-9 at day 6 post C. jejuni strain 81-176 infection. Whereas the pathogen readily colonized the intestines of infant IL-18^–/– mice only, colonic mucin-2 mRNA, a pivotal mucus constituent, was downregulated in IL-22^–/– mice and accompanied by increased expression of pro-inflammatory cytokines including IFN-γ, TNF, IL-17A, and IL-1β. Furthermore, in both naive and infected IL-22^–/– mice, colonic expression of IL-23p19 and IL-18 was lower as compared to wildtype mice, whereas, conversely, colonic IL-22 mRNA levels were lower in IL-18^–/– and colonic IL-18 expression lower in IL-23p19^–/– as compared to wildtype mice. Moreover, colonic expression of MMP-2 and MMP-9 and their endogenous inhibitor TIMP-1 were lower in IL-22^–/– as compared to wildtype mice at day 6 postinfection. In conclusion, mediators belonging of the IL-23/IL-22/IL-18 axis as well as the gelatinases MMP-2 and MMP-9 are involved in mediating campylobacteriosis of infant mice in a differentially regulated fashion.

Enteric Pathogens Exploit the Microbiota-generated Nutritional Environment of the Gut

Host bacterial associations have a profound impact on health and disease. The human gastrointestinal (GI) tract is inhabited by trillions of commensal bacteria that aid in the digestion of food and vitamin production and play crucial roles in human physiology. Disruption of these relationships and the structure of the bacterial communities that inhabit the gut can contribute to dysbiosis, leading to disease. This fundamental relationship between the host and microbiota relies on chemical signaling and nutrient availability and exchange. GI pathogens compete with the endogenous microbiota for a colonization niche (1, 2). The ability to monitor nutrients and combine this information with the host physiological state is important for the pathogen to precisely program the expression of its virulence repertoire. A major nutrient source is carbon, and although the impact of carbon nutrition on the colonization of the gut by the microbiota has been extensively studied, the extent to which carbon sources affect the regulation of virulence factors by invading pathogens has not been fully defined. The GI pathogen enterohemorrhagic E. coli (EHEC) gages sugar sources as an important cue to regulate expression of its virulence genes. EHEC senses whether it is in a gluconeogenic versus a glycolytic environment, as well as fluctuations of fucose levels to fine tune regulation of its virulence repertoire.

Intestinal Expression of Genes Encoding Inflammatory Mediators and Gelatinases During Arcobacter Butzleri Infection of Gnotobiotic Il-10 Deficient Mice

We have previously shown that Arcobacter butzleri induces intestinal, extra-intestinal, and systemic immune responses in perorally infected gnotobiotic IL-10(-/-) mice in a strain-dependent fashion. Here, we present a comprehensive survey of small and large intestinal expression profiles of inflammatory and regulatory mediators as well as of the matrix-degrading gelatinases MMP-2 and MMP-9 following murine A. butzleri infection. Gnotobiotic IL-10(-/-) mice were infected with A. butzleri strains CCUG 30485 or C1 of human and chicken origin, respectively. At day 6 following A. butzleri infection, mucin-2 mRNA, an integral part of the intestinal mucus layer, was downregulated in the colon, whereas TNF and IL-23p19 mRNA were upregulated in the ileum. Furthermore, IFN-γ, IL-17A, IL-1β, and IL-22 mRNA were upregulated in both colonic and ileal ex vivo biopsies at day 6 post strain CCUG 30485 infection. These changes were accompanied by downregulated colonic MMP-9 levels, whereas both MMP-2 and MMP-9 mRNA were upregulated in the ileum. In conclusion, these data indicate that A. butzleri infection induces changes in the expression of genes involved in pro-inflammatory and regulatory immune responses as well as in tissue degradation.

Identification of Novel Components Influencing Colonization Factor Antigen I Expression in Enterotoxigenic Escherichia coli

Colonization factors (CFs) mediate early adhesion of Enterotoxigenic Escherichia coli (ETEC) in the small intestine. Environmental signals including bile, glucose, and contact with epithelial cells have previously been shown to modulate CF expression in a strain dependent manner. To identify novel components modulating CF surface expression, 20 components relevant to the intestinal environment were selected for evaluation. These included mucin, bicarbonate, norepinephrine, lincomycin, carbon sources, and cations. Effects of individual components on surface expression of the archetype CF, CFA/I, were screened using a fractional factorial Hadamard matrix incorporating 24 growth conditions. As most CFs agglutinate erythrocytes, surface expression was evaluated by mannose resistant hemagglutination. Seven components, including porcine gastric mucin, lincomycin, glutamine, and glucose were found to induce CFA/I surface expression in vitro in a minimal media while five others were inhibitory, including leucine and 1,10-phenanthroline. To further explore the effect of components positively influencing CFA/I surface expression, a response surface methodology (RSM) was designed incorporating 36 growth conditions. The optimum concentration for each component was identified, thereby generating a novel culture media, SP1, for CFA/I expression. CFs closely related to CFA/I, including CS4 and CS14 were similarly induced in SP1 media. Other epidemiologically relevant CFs were also induced when compared to the level obtained in minimal media. These results indicate that although CF surface expression is complex and highly variable among strains, the CF response can be predicted for closely related strains. A novel culture media inducing CFs in the CF5a group was successfully identified. In addition, mucin was found to positively influence CF expression in strains expressing either CFA/I or CS1 and CS3, and may function as a common environmental cue.

Mucosal physical and chemical innate barriers: Lessons from microbial evasion strategies

The innate immune system has evolved since millions of years under a selective pressure. Among the different host mechanisms selected and conserved as a first line of defense, the gastrointestinal mucus layer constitutes an efficient physical and chemical barrier against invading microbes. Mucin glycoproteins and antimicrobial peptides are the major components of the mucus barrier, and evidences prove that they form an effective protection against most microbes. However, successful pathogens have evolved evasion strategies to circumvent this defense barrier. Here, we discuss the interactions between pathogens, mucins, and antimicrobial peptides, and the mechanisms that pathogens have developed to evade the innate defense systems of the intestinal mucosal barrier.

Identification of O-glycan Structures from Chicken Intestinal Mucins Provides Insight into Campylobactor jejuni Pathogenicity

The Gram-negative bacteria Campylobactor jejuni is the primary bacteria responsible for food poisoning in industrialized countries, and acute diarrheal illness is a leading cause of mortality among children in developing countries. C. jejuni are commensal in chickens. They are particularly abundant in the caecal crypts, and poultry products are commonly infected as a result of cross-contamination during processing. The interactions between C. jejuni and chicken intestinal tissues as well as the pathogenic molecular mechanisms of colonization in humans are unknown, but identifying these factors could provide potential targets to reduce the incidence of campylobacteriosis. Recently, purified chicken intestinal mucin was shown to attenuate adherence and invasion of C. jejuni in the human colorectal adenocarcinoma cell line HCT-8 in vitro, and this effect was attributed to mucin O-glycosylation. Mucins from different regions of the chicken intestine inhibited C. jejuni binding and internalization differentially, with large intestine>small intestine>caecum. Here, we use LC-MS to perform a detailed structural analysis of O-glycans released from mucins purified from chicken large intestine, small intestine, and caecum. The O-glycans identified were abundantly sulfated compared with the human intestines, and sulfate moieties were present throughout the chicken intestinal tract. Interestingly, alpha 1-2 linked fucose residues, which have a high binding affinity to C. jejuni, were identified in the small and large intestines. Additionally, N-glycolylneuraminic/N-acetylneuraminic acid containing structures present as Sd(a)-like epitopes were identified in large intestine samples but not small intestine or caecum. O-glycan structural characterization of chicken intestinal mucins provides insights into adherence and invasion properties of C. jejuni, and may offer prospective candidate molecules aimed at reducing the incidence of infection.

The mucus and mucins of the goblet cells and enterocytes provide the first defense line of the gastrointestinal tract and interact with the immune system

The gastrointestinal tract is covered by mucus that has different properties in the stomach, small intestine, and colon. The large highly glycosylated gel-forming mucins MUC2 and MUC5AC are the major components of the mucus in the intestine and stomach, respectively. In the small intestine, mucus limits the number of bacteria that can reach the epithelium and the Peyer's patches. In the large intestine, the inner mucus layer separates the commensal bacteria from the host epithelium. The outer colonic mucus layer is the natural habitat for the commensal bacteria. The intestinal goblet cells secrete not only the MUC2 mucin but also a number of typical mucus components: CLCA1, FCGBP, AGR2, ZG16, and TFF3. The goblet cells have recently been shown to have a novel gate-keeping role for the presentation of oral antigens to the immune system. Goblet cells deliver small intestinal luminal material to the lamina propria dendritic cells of the tolerogenic CD103(+) type. In addition to the gel-forming mucins, the transmembrane mucins MUC3, MUC12, and MUC17 form the enterocyte glycocalyx that can reach about a micrometer out from the brush border. The MUC17 mucin can shuttle from a surface to an intracellular vesicle localization, suggesting that enterocytes might control and report epithelial microbial challenge. There is communication not only from the epithelial cells to the immune system but also in the opposite direction. One example of this is IL10 that can affect and improve the properties of the inner colonic mucus layer. The mucus and epithelial cells of the gastrointestinal tract are the primary gate keepers and controllers of bacterial interactions with the host immune system, but our understanding of this relationship is still in its infancy.