Distinct effects of Vibrio cholerae haemagglutinin/protease on the structure and localization of the tight junction-associated proteins occludin and ZO-1

Cleavage of cell junction proteins as a host invasion strategy in leptospirosis

Infection and invasion are the prerequisites for developing the disease symptoms in a host. While the probable mechanism of host invasion and pathogenesis is known in many pathogens, very little information is available on Leptospira invasion/pathogenesis. For causing systemic infection Leptospira must transmigrate across epithelial barriers, which is the most critical and challenging step. Extracellular and membrane-bound proteases play a crucial role in the invasion process. An extensive search for the proteins experimentally proven to be involved in the invasion process through cell junction cleavage in other pathogens has resulted in identifying 26 proteins. The similarity searches on the Leptospira genome for counterparts of these 26 pathogenesis-related proteins identified at least 12 probable coding sequences. The proteins were either extracellular or membrane-bound with a proteolytic domain to cleave the cell junction proteins. This review will emphasize our current understanding of the pathogenic aspects of host cell junction-pathogenic protein interactions involved in the invasion process. Further, potential candidate proteins with cell junction cleavage properties that may be exploited in the diagnostic/therapeutic aspects of leptospirosis will also be discussed. KEY POINTS: • The review focussed on the cell junction cleavage proteins in bacterial pathogenesis • Cell junction disruptors from Leptospira genome are identified using bioinformatics • The review provides insights into the therapeutic/diagnostic interventions possible.

Border Control: The Role of the Microbiome in Regulating Epithelial Barrier Function

The gut mucosal epithelium is one of the largest organs in the body and plays a critical role in regulating the crosstalk between the resident microbiome and the host. To this effect, the tight control of what is permitted through this barrier is of high importance. There should be restricted passage of harmful microorganisms and antigens while at the same time allowing the absorption of nutrients and water. An increased gut permeability, or "leaky gut", has been associated with a variety of diseases ranging from infections, metabolic diseases, and inflammatory and autoimmune diseases to neurological conditions. Several factors can affect gut permeability, including cytokines, dietary components, and the gut microbiome. Here, we discuss how the gut microbiome impacts the permeability of the gut epithelial barrier and how this can be harnessed for therapeutic purposes.

Immune evasion and persistence in enteric bacterial pathogens

The major function of the mammalian immune system is to prevent and control infections caused by enteropathogens that collectively have altered human destiny. In fact, as the gastrointestinal tissues are the major interface of mammals with the environment, up to 70% of the human immune system is dedicated to patrolling them The defenses are multi-tiered and include the endogenous microflora that mediate colonization resistance as well as physical barriers intended to compartmentalize infections. The gastrointestinal tract and associated lymphoid tissue are also protected by sophisticated interleaved arrays of active innate and adaptive immune defenses. Remarkably, some bacterial enteropathogens have acquired an arsenal of virulence factors with which they neutralize all these formidable barriers to infection, causing disease ranging from mild self-limiting gastroenteritis to in some cases devastating human disease.

The emerging roles of bacterial proteases in intestinal diseases

Proteases are an evolutionarily conserved family of enzymes that degrade peptide bonds and have been implicated in several common gastrointestinal (GI) diseases. Although luminal proteolytic activity is important for maintenance of homeostasis and health, the current review describes recent advances in our understanding of how overactivity of luminal proteases contributes to the pathophysiology of celiac disease, irritable bowel syndrome, inflammatory bowel disease and GI infections. Luminal proteases, many of which are produced by the microbiota, can modulate the immunogenicity of dietary antigens, reduce mucosal barrier function and activate pro-inflammatory and pro-nociceptive host signaling. Increased proteolytic activity has been ascribed to both increases in protease production and decreases in inhibitors of luminal proteases. With the identification of strains of bacteria that are important sources of proteases and their inhibitors, the stage is set to develop drug or microbial therapies to restore protease balance and alleviate disease.

From intestinal colonization to systemic infections: Candida albicans translocation and dissemination

Candida species are the most prevalent cause of invasive fungal infections, of which Candida albicans is the most common. Translocation across the epithelial barrier into the bloodstream by intestinal-colonizing C. albicans cells serves as the main source for systemic infections. Understanding the fungal mechanisms behind this process will give valuable insights on how to prevent such infections and keep C. albicans in the commensal state in patients with predisposing conditions. This review will focus on recent developments in characterizing fungal translocation mechanisms, compare what we know about enteric bacterial pathogens with C. albicans, and discuss the different proposed hypotheses for how C. albicans enters and disseminates through the bloodstream immediately following translocation.

Pharmacokinetic Differences of Wuji Pill Components in Normal and Chronic Visceral Hypersensitivity Irritable Bowel Syndrome Rats Attributable to Changes in Tight Junction and Transporters

The Wuji pill, also called Wuji Wan (WJW), is an effective traditional medicine for the clinical treatment of irritable bowel syndrome (IBS). It is principally composed of Rhizoma Coptidis, Fructus Evodiae Rutaecarpae, and Radix Paeoniae Alba. There have been no reports on the pharmacokinetics of WJW on IBS. Because it is more meaningful to study pharmacokinetics in relation to specific pathological conditions, our study investigated the pharmacokinetic differences of five representative components (berberine, palmatine, evodiamine, rutaecarpine, and paeoniflorin) in normal rats and chronic visceral hypersensitivity IBS (CVH-IBS) model rats after single dose and multiple doses of WJW using ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Transmission electron microscopy, immunohistochemistry, and immunofluorescence were used to explore mechanisms behind the pharmacokinetic differences in terms of tight junction proteins (Occludin and ZO-1), myosin light chain kinase (MLCK), and transporters including P-glycoprotein (P-gp), multidrug resistance associated protein 1 (MRP1), and multidrug resistance associated protein 2 (MRP2) in rat colons. After a single dose, for all components except rutaecarpine, significant differences were observed between normal and model groups. Compared with normal group, T_1/2 and AUC_0-t of berberine and palmatine in model group increased significantly (562.5 ± 237.2 vs. 1,384.9 ± 712.4 min, 733.8 ± 67.4 vs. 1,532.4 ± 612.7 min; 5,443.0 ± 1,405.8 vs. 9,930.8 ± 2,304.5 min·ng/ml, 2,365.5 ± 410.6 vs. 3,527.0 ± 717.8 min·ng/ml), while Cl/F decreased (840.7 ± 250.8 vs. 397.3 ± 142.7 L/h/kg, 427.7 ± 89.4 vs. 288.9 ± 114.4 L/h/kg). C_max and AUC_0-t of evodiamine in model group increased significantly (1.4 ± 0.6 vs. 2.4 ± 0.7 ng/ml; 573 ± 45.3 vs. 733.9 ± 160.2 min·ng/ml), while T_1/2, T_max, Cl/F, and Vd/F had no significant difference. T_max and AUC_0-t of paeoniflorin in model group increased significantly (21.0 ± 8.2 vs. 80.0 ± 45.8 min; 15,428.9 ± 5,063.6 vs. 33,140.6 ± 5,613.9 min·ng/ml), while Cl/F decreased (110.5 ± 48.1 vs. 43.3 ± 9.5 L/h/kg). However, after multiple doses, all five components showed significant differences between normal and model groups. Moreover, these differences were related to tight junction damage and the differential expression of transporters in the colon, suggesting that dose adjustment might be required during administration of WJW in the clinical treatment of IBS.

Low potassium disrupt intestinal barrier and result in bacterial translocation

Background

Bacterial translocation was observed in critical illness and patients with chronic diseases such as liver cirrhosis and chronic kidney disease (CKD). Hypokalemia is a common complication in these diseases. Whether low potassium diet may increase intestinal permeability and result in bacterial translocation lack of evidence. The present study was aimed to investigate the potential effects of LK on intestinal permeability.

Methods

Grade 8-week-old male Bal B/C mice were randomly placed either on a normal potassium (NK) mouse chow or a low potassium (LK) diet for 28 days. Intestinal permeability and expression of tight junction proteins were compared between the two groups.

Results

Compared with the NK group, the mice in LK group had significantly lower serum potassium level, increased levels of plasmas endotoxin and plasma d-lactate. The bacterial translocation was higher and in occurred mainly in mesenteric lymph nodes (MLN), liver and spleen. The pathologic change of small intestine was obvious with thinner villus lamina propria, shorter crypt depth and thinner intestinal wall. Slight increases in the expression of proteins and mRNA levels of both claudin-1 and claudin-2 were observed in LK group.

Conclusions

Low potassium diet could increase intestinal permeability and thereby lead to bacterial translocation, which was suspected to result from impaired intestinal epithelial barrier and biological barrier.

Impact of Epithelial Cell Shedding on Intestinal Homeostasis

The gut barrier acts as a first line of defense in the body, and plays a vital role in nutrition and immunoregulation. A layer of epithelial cells bound together via intercellular junction proteins maintains intestinal barrier integrity. Based on a tight equilibrium between cell extrusion and cell restitution, the renewal of the epithelium (epithelial turnover) permits the preservation of cell numbers. As the last step within the epithelial turnover, cell shedding occurs due to the pressure of cell division and migration from the base of the crypt. During this process, redistribution of tight junction proteins enables the sealing of the epithelial gap left by the extruded cell, and thereby maintains barrier function. Disturbance in cell shedding can create transient gaps (leaky gut) or cell accumulation in the epithelial layer. In fact, numerous studies have described the association between dysregulated cell shedding and infection, inflammation, and cancer; thus epithelial cell extrusion is considered a key defense mechanism. In the gastrointestinal tract, altered cell shedding has been observed in mouse models of intestinal inflammation and appears as a potential cause of barrier loss in human inflammatory bowel disease (IBD). Despite the relevance of this process, there are many unanswered questions regarding cell shedding. The investigation of those mechanisms controlling cell extrusion in the gut will definitely contribute to our understanding of intestinal homeostasis. In this review, we summarized the current knowledge about intestinal cell shedding under both physiological and pathological circumstances.

Unraveling enterohemorrhagic Escherichia coli infection: the promising role of dietary compounds and probiotics in bacterial elimination and host innate immunity boosting

The innate immune system has developed sophisticated strategies to defense against infections. Host cells utilize the recognition machineries such as toll-like receptors and nucleotide binding and oligomerization domain-like receptors to identify the pathogens and alert immune system. However, some pathogens have developed tactics to evade host defenses, including manipulation of host inflammatory response, interference with cell death pathway, and highjack of phagocytosis signaling for a better survival and colonization in host. Enterohemorrhagic Escherichia coli (EHEC) is a notorious foodborne pathogen that causes severe tissue damages and gastrointestinal diseases, which has been reported to disturb host immune responses. Diverse bioactive compounds such as flavonoids, phenolic acids, alkaloids, saccharides, and terpenoids derived from food varieties and probiotics have been discovered and investigated for their capability of combating bacterial infections. Some of them serve as novel antimicrobial agents and act as immune boosters that harness host immune system. In this review, we will discuss how EHEC, specifically E. coli O157:H7, hijacks the host immune system and interferes with host signaling pathway; and highlight the promising role of food-derived bioactive compounds and probiotics in harnessing host innate immunity and eliminating E. coli O157:H7 infection with multiple strategies.

Tight Junctions as a Key for Pathogens Invasion in Intestinal Epithelial Cells

Tight junctions play a major role in maintaining the integrity and impermeability of the intestinal barrier. As such, they act as an ideal target for pathogens to promote their translocation through the intestinal mucosa and invade their host. Different strategies are used by pathogens, aimed at directly destabilizing the junctional network or modulating the different signaling pathways involved in the modulation of these junctions. After a brief presentation of the organization and modulation of tight junctions, we provide the state of the art of the molecular mechanisms leading to permeability breakdown of the gut barrier as a consequence of tight junctions’ attack by pathogens, including bacteria, viruses, fungi, and parasites.

The possible mechanism of the protective effect of a sulfated polysaccharide from Gracilaria Lemaneiformis against colitis induced by dextran sulfate sodium in mice

This study aimed to investigate the possible mechanism of the protective effect of a sulfated polysaccharide (SP) from Gracilaria Lemaneiformis against colitis induced by dextran sulfate sodium (DSS). Balb/c mice were gavaged with SP for four weeks, then colon tissue, cecal contents and feces were collected for further analysis. Results showed that SP was effective for inhibiting colon shortening and oedema forming. It could alleviate colonic inflammation via down-regulating the expression of tumor necrosis factor-α (TNF-α), interleukin (IL-6, IL-1β). Besides, it enhanced the intestinal barrier by up-regulating the expression of tight junction proteins Claudin-1 and Zonula occludens-1 (ZO-1) as well as Mucin (MUC-2). The increased expression of short chain fatty acid (SCFA) receptors including G protein-coupled receptor (GPR43, GPR109A) and olfactory receptor (Olfr78), and SCFA production in feces indicated that most of SCFA were absorbed in colon, which could play positive roles in ameliorating colitis. Furthermore, the results of gut microbiota showed that Enterorhabdus, Desulfovibrio, Alistipes, Bacteroides acidifaciens had closest correlations with the strongest protective effects against colitis. Therefore, SP could alleviate DSS-induced colitis via enhancing intestinal barrier, reducing inflammation, activating SCFA receptors and regulating gut microbiota. It could be developed as functional foods which is good for gut health.

The small intestine: barrier, permeability and microbiota

In recent years, there has been growing interest in the comprehension of the physiology of intestinal permeability and microbiota; and how these elements could influence the pathogenesis of diseases. The term intestinal permeability describes all the processes that allow the passage of molecules as water, electrolytes and nutrients through the intestinal barrier by the paracellular or the transcellular transport systems with several implications for self-tolerance and not-self immunity. An increased permeability might induce a more significant interaction of the immune system with unknown external antigens. This might favor the onset of several immune-related extra-intestinal diseases including coeliac disease, diabetes mellitus type 1, bronchial asthma and inflammatory bowel diseases. Furthermore, the intestinal permeability interacts every day with microbiota, the complex system of mutualistic inhabitants and commensal microorganisms living in the healthy gut. Microbiota is implicated in physiological functions by actively participating in digestion, absorption, synthesis of vitamins and protection from external aggressions. The critical site where these processes occur is the small intestine to which this updated review is dedicated. Understanding its anatomy, its barrier structure and permeability modulation and its microbiota composition is the essential skill to comprehend the complex pathogenesis of several - not only gastroenterological - diseases.

Virulence Regulation and Innate Host Response in the Pathogenicity of Vibrio cholerae

The human pathogen Vibrio cholerae is the causative agent of severe diarrheal disease known as cholera. Of the more than 200 "O" serogroups of this pathogen, O1 and O139 cause cholera outbreaks and epidemics. The rest of the serogroups, collectively known as non-O1/non-O139 cause sporadic moderate or mild diarrhea and also systemic infections. Pathogenic V. cholerae circulates between nutrient-rich human gut and nutrient-deprived aquatic environment. As an autochthonous bacterium in the environment and as a human pathogen, V. cholerae maintains its survival and proliferation in these two niches. Growth in the gastrointestinal tract involves expression of several genes that provide bacterial resistance against host factors. An intricate regulatory program involving extracellular signaling inputs is also controlling this function. On the other hand, the ability to store carbon as glycogen facilitates bacterial fitness in the aquatic environment. To initiate the infection, V. cholerae must colonize the small intestine after successfully passing through the acid barrier in the stomach and survive in the presence of bile and antimicrobial peptides in the intestinal lumen and mucus, respectively. In V. cholerae, virulence is a multilocus phenomenon with a large functionally associated network. More than 200 proteins have been identified that are functionally linked to the virulence-associated genes of the pathogen. Several of these genes have a role to play in virulence and/or in functions that have importance in the human host or the environment. A total of 524 genes are differentially expressed in classical and El Tor strains, the two biotypes of V. cholerae serogroup O1. Within the host, many immune and biological factors are able to induce genes that are responsible for survival, colonization, and virulence. The innate host immune response to V. cholerae infection includes activation of several immune protein complexes, receptor-mediated signaling pathways, and other bactericidal proteins. This article presents an overview of regulation of important virulence factors in V. cholerae and host response in the context of pathogenesis.

Phenotypic and Genotypic Properties of Vibrio cholerae non-O1, non-O139 Isolates Recovered from Domestic Ducks in Germany

Vibrio cholerae non-O1, non-O139 bacteria are natural inhabitants of aquatic ecosystems and have been sporadically associated with human infections. They mostly lack the two major virulence factors of toxigenic V. cholerae serogroups O1 and O139 strains, which are the causative agent of cholera. Non-O1, non-O139 strains are found in water bodies, sediments, and in association with other aquatic organisms. Occurrence of these bacteria in fecal specimens of waterfowl were reported, and migratory birds likely contribute to the long-distance transfer of strains. We investigated four V. cholerae non-O1, non-O139 isolates for phenotypic traits and by whole genome sequencing (WGS). The isolates were recovered from organs of domestic ducks with serious disease symptoms. WGS data revealed only a distant genetic relationship between all isolates. The isolates harbored a number of virulence factors found in most V. cholerae strains. Specific virulence factors of non-O1, non-O139 strains, such as the type III secretion system (TTSS) or cholix toxin, were observed. An interesting observation is that all isolates possess multifunctional autoprocessing repeats-in-toxin toxins (MARTX) closely related to the MARTX of toxigenic El Tor O1 strains. Different primary sequences of the abundant OmpU proteins could indicate a significant role of this virulence factor. Phenotypic characteristics such as hemolysis and antimicrobial resistance (AMR) were studied. Three isolates showed susceptibility to a number of tested antimicrobials, and one strain possessed AMR genes located in an integron. Knowledge of the environmental occurrence of V. cholerae non-O1, non-O139 in Germany is limited. The source of the infection of the ducks is currently unknown. In the context of the ‘One Health’ concept, it is desirable to study the ecology of V. cholerae non-O1, non-O139, as it cannot be excluded that the isolates possess zoonotic potential and could cause infections in humans.

Proton pump inhibitors enhance intestinal permeability via dysbiosis of gut microbiota under stressed conditions in mice

BACKGROUND

Intestinal permeability and psychological stress are considered the key mechanism(s) in functional dyspepsia (FD). Although proton pump inhibitors (PPIs) are commonly used for the treatment of FD, the effect of PPIs on intestinal permeability has not been elucidated. This study investigated the effect of PPI on intestinal permeability under stressed conditions.

METHODS

C57BL/6J mice were subjected to water avoidance stress (WAS) and administered rabeprazole (40 mg/kg) or vehicle treatment (VT). We then evaluated intestinal permeability both in vivo and ex vivo using plasma fluorescein isothiocyanate-dextran and by assessing the paracellular permeability and transepithelial electrical resistance (TEER) in an Ussing chamber, respectively. Furthermore, we evaluated the effect of PPI-treated fecal microbiota transplant (FMT) on intestinal permeability in vivo. Microbiota profiles of donor feces were assessed by 16S rRNA gene analysis using MiSeq and QIIME2.

KEY RESULTS

In the WAS treatment, PPI significantly enhanced intestinal permeability in vivo compared to that in VT. Moreover, PPI significantly increased paracellular permeability and decreased TEER in the duodenum and jejunum, respectively, compared to those in VT under stressed conditions. Moreover, both vasoactive intestinal peptide (VIP) receptor antagonist and ketotifen significantly reversed the effect of PPI on intestinal permeability. Furthermore, PPI-treated FMT significantly increased the intestinal permeability in vivo compared to that in vehicle-treated FMT. Proton pump inhibitors treatment altered the gut microbiota composition, indicating that PPI induced dysbiosis.

CONCLUSIONS AND INFERENCES

Under stressed conditions, PPI enhances intestinal permeability via dysbiosis of gut microbiota. Vasoactive intestinal peptide and mast cells are also implicated in the underlying mechanisms.

Vibrio cholerae non-O1 - the first reported case of keratitis in a healthy patient

Background

Vibrio cholerae non-O1 is a virulent pathogen that causes significant morbidity and mortality in humans. Herein, we report a case of corneal ulcer caused by this pathogen.

Case presentation

A 59-year-old fisherman with no systemic history was struck in the right eye by a marine shrimp and developed keratitis. Corneal scrapping culture revealed the presence of the V. cholerae non-O1, and its identification was confirmed by Analytical Profile Index 20E system and polymerase chain reaction. He was successfully treated with topical levofloxacin (0.3%) and fortified amikacin (12.5 mg/mL) for 2 weeks. The visual acuity recovered to 20/25 after treatment without complications.

Conclusions

This is the first case report of keratitis caused by V. cholerae non-O1 strain. Ocular injury by marine creatures and contaminated seawater can contribute to severe corneal ulcer. Early diagnosis can be achieved by meticulous history taking and a comprehensive laboratory workup. Simultaneously, an effective antibiotic therapy can lead to a positive outcome.

Environmental and Clinical Strains of Vibrio cholerae Non-O1, Non-O139 From Germany Possess Similar Virulence Gene Profiles

Vibrio cholerae is a natural inhabitant of aquatic ecosystems globally. Strains of the serogroups O1 and O139 cause the epidemic diarrheal disease cholera. In Northern European waters, V. cholerae bacteria belonging to other serogroups (designated non-O1, non-O139) are present, of which some strains have been associated with gastrointestinal infections or extraintestinal infections, like wound infections or otitis. For this study, environmental strains from the German coastal waters of the North Sea and the Baltic Sea were selected (100 strains) and compared to clinical strains (10 isolates) that were from patients who contracted the infections in the same geographical region. The strains were characterized by MLST and examined by PCR for the presence of virulence genes encoding the cholera toxin, the toxin-coregulated pilus (TCP), and other virulence-associated accessory factors. The latter group comprised hemolysins, RTX toxins, cholix toxin, pandemic islands, and type III secretion system (TTSS). Phenotypic assays for hemolytic activity against human and sheep erythrocytes were also performed. The results of the MLST analysis revealed a considerable heterogeneity of sequence types (in total 74 STs). The presence of virulence genes was also variable and 30 profiles were obtained by PCR. One profile was found in 38 environmental strains and six clinical strains. Whole genome sequencing (WGS) was performed on 15 environmental and 7 clinical strains that were ST locus variants in one, two, or three alleles. Comparison of WGS results revealed that a set of virulence genes found in some clinical strains is also present in most environmental strains irrespective of the ST. In few strains, more virulence factors are acquired through horizontal gene transfer (i.e., TTSS, genomic islands). A distinction between clinical and environmental strains based on virulence gene profiles is not possible for our strains. Probably, many virulence traits of V. cholerae evolved in response to biotic and abiotic pressure and serve adaptation purposes in the natural aquatic environment, but provide a prerequisite for infection of susceptible human hosts. These findings indicate the need for surveillance of Vibrio spp. in Germany, as due to global warming abundance of Vibrio will rise and infections are predicted to increase.

The pathogenicity characterization of non-O1 Vibrio cholerae and its activation on immune system in freshwater shrimp Macrobrachium nipponense

Outbreaks of mass mortalities among cultured Macrobrachium nipponense occurred in a commercial hatchery during the autumn of 2017 in Jiangsu province, P. R. China, and non-O1 Vibrio cholerae was isolated and identified as causal agents of M. nipponense, with a LD₅₀ value 4.09 × 10⁴ CFU/mL. Detection of virulence-associated genes by PCR indicated that XL1 was positive for Mp, HlyA, RtxA, OmpU, Ace, Zot and T6SS. Furthermore, the results of extracellular enzyme analysis revealed that the strain can produce lecithinase, amylase, gelatinase and hemolysin. Histopathological analysis revealed that the hepatic tubule lumen and the gap between the hepatic tubules became larger, and the brush border disappeared in the hepatopancreas. Quantitive real-time PCR (qRT-PCR) was undertaken to measure mRNA expression levels for thirteen immune related genes in M. nipponense after non-O1 V. cholerae infection. The transcriptional analysis of these immune related genes demonstrated that the expression levels of dorsal, relish, p38, crustin1, crustin2, crustin3, hemocyanin, i-lysozyme, anti-lipopolysaccharide factors 1, anti-lipopolysaccharide factors 2, prophenoloxidase were significantly up-regulated in hemolymph of M. nipponense post-infection. These results revealed varying expression profiles and clear transcriptional activation of these immune related genes in hemolymph, which will contribute to better understand the pathogenesis and host defensive system in non-O1 V. cholerae invasion.

Campylobacter jejuni enters gut epithelial cells and impairs intestinal barrier function through cleavage of occludin by serine protease HtrA

Campylobacter jejuni secretes HtrA (high temperature requirement protein A), a serine protease that is involved in virulence. Here, we investigated the interaction of HtrA with the host protein occludin, a tight junction strand component. Immunofluorescence studies demonstrated that infection of polarized intestinal Caco-2 cells with C. jejuni strain 81-176 resulted in a redistribution of occludin away from the tight junctions into the cytoplasm, an effect that was also observed in human biopsies during acute campylobacteriosis. Occludin knockout Caco-2 cells were generated by CRISPR/Cas9 technology. Inactivation of this gene affected the polarization of the cells in monolayers and transepithelial electrical resistance (TER) was reduced, compared to wild-type Caco-2 cells. Although tight junctions were still being formed, occludin deficiency resulted in a slight decrease of the tight junction plaque protein ZO-1, which was redistributed off the tight junction into the lateral plasma membrane. Adherence of C. jejuni to Caco-2 cell monolayers was similar between the occludin knockout compared to wild-type cells, but invasion was enhanced, indicating that deletion of occludin allowed larger numbers of bacteria to pass the tight junctions and to reach basal membranes to target the fibronectin receptor followed by cell entry. Finally, we discovered that purified C. jejuni HtrA cleaves recombinant occludin in vitro to release a 37 kDa carboxy-terminal fragment. The same cleavage fragment was observed in Western blots upon infection of polarized Caco-2 cells with wild-type C. jejuni, but not with isogenic ΔhtrA mutants. HtrA cleavage was mapped to the second extracellular loop of occludin, and a putative cleavage site was identified. In conclusion, HtrA functions as a secreted protease targeting the tight junctions, which enables the bacteria by cleaving occludin and subcellular redistribution of other tight junction proteins to transmigrate using a paracellular mechanism and subsequently invade epithelial cells.

Crossing the Intestinal Barrier via Listeria Adhesion Protein and Internalin A

The intestinal epithelial cell lining provides the first line of defense, yet foodborne pathogens such as Listeria monocytogenes can overcome this barrier; however, the underlying mechanism is not well understood. Though the host M cells in Peyer's patch and the bacterial invasion protein internalin A (InlA) are involved, L. monocytogenes can cross the gut barrier in their absence. The interaction of Listeria adhesion protein (LAP) with the host cell receptor (heat shock protein 60) disrupts the epithelial barrier, promoting bacterial translocation. InlA aids L. monocytogenes transcytosis via interaction with the E-cadherin receptor, which is facilitated by epithelial cell extrusion and goblet cell exocytosis; however, LAP-induced cell junction opening may be an alternative bacterial strategy for InlA access to E-cadherin and its translocation. Here, we summarize the strategies that L. monocytogenes employs to circumvent the intestinal epithelial barrier and compare and contrast these strategies with other enteric bacterial pathogens. Additionally, we provide implications of recent findings for food safety regulations.

Mechanisms by which gut microorganisms influence food sensitivities

Finely tuned mechanisms enable the gastrointestinal tract to break down dietary components into nutrients without mounting, in the majority of cases, a dysregulated immune or functional host response. However, adverse reactions to food have been steadily increasing, and evidence suggests that this process is environmental. Adverse food reactions can be divided according to their underlying pathophysiology into food intolerances, when, for instance, there is deficiency of a host enzyme required to digest the food component, and food sensitivities, when immune mechanisms are involved. In this Review, we discuss the clinical and experimental evidence for enteric infections and/or alterations in the gut microbiota in inciting food sensitivity. We focus on mechanisms by which microorganisms might provide direct pro-inflammatory signals to the host promoting breakdown of oral tolerance to food antigens or indirect pathways that involve the metabolism of protein antigens and other dietary components by gut microorganisms. Better understanding of these mechanisms will help in the development of preventive and therapeutic strategies for food sensitivities.

Comparative genomics for non-O1/O139 Vibrio cholerae isolates recovered from the Yangtze River Estuary versus V. cholerae representative isolates from serogroup O1

Vibriocholerae, which is autochthonous to estuaries worldwide, can cause human cholera that is still pandemic in developing countries. A number of V. cholerae isolates of clinical and environmental origin worldwide have been subjected to genome sequencing to address their phylogenesis and bacterial pathogenesis, however, little genome information is available for V. cholerae isolates derived from estuaries, particularly in China. In this study, we determined the complete genome sequence of V. cholerae CHN108B (non-O1/O139 serogroup) isolated from the Yangtze River Estuary, China and performed comparative genome analysis between CHN108B and other eight representative V. cholerae isolates. The 4,168,545-bp V. cholerae CHN108B genome (47.2% G+C) consists of two circular chromosomes with 3,691 predicted protein-encoding genes. It has 110 strain-specific genes, the highest number among the eight representative V. cholerae whole genomes from serogroup O1: there are seven clinical isolates linked to cholera pandemics (1937-2010) and one environmental isolate from Brazil. Various mobile genetic elements (such as insertion sequences, prophages, integrative and conjugative elements, and super-integrons) were identified in the nine V. cholerae genomes of clinical and environmental origin, indicating that the bacterium undergoes extensive genetic recombination via lateral gene transfer. Comparative genomics also revealed different virulence and antimicrobial resistance gene patterns among the V. cholerae isolates, suggesting some potential virulence factors and the rising development of resistance among pathogenic V. cholerae. Additionally, draft genome sequences of multiple V. cholerae isolates recovered from the Yangtze River Estuary were also determined, and comparative genomics revealed many genes involved in specific metabolism pathways, which are likely shaped by the unique estuary environment. These results provide additional evidence of V. cholerae genome plasticity and will facilitate better understanding of the genome evolution and pathogenesis of this severe water-borne pathogen worldwide.

Vibrio cholerae embraces two major evolutionary traits as revealed by targeted gene sequencing

Vibrio cholerae inhabits aquatic environments worldwide and has over 200 recognized serogroups classified by O-polysaccharide specificity. Here, we report that V. cholerae selects either of two genetic traits during their evolution. Sequencing of the specific gene locus MS6_A0927 revealed that 339 of 341 strains of V. cholerae and closely related Vibrio species originating from 34 countries over a century carried either metY (M) (~1,269 bp) or luxR-hchA (LH) (~1,600 bp) genes, and consequently those vibrios were separated into two clusters, M (45.4%) and LH (54.6%). Only two strains contained both M and LH in the same locus. Moreover, extensive polymorphisms in those genes were detected in M and LH with 79 and 46 sequence variations, respectively. V. cholerae O1 strains isolated from cholera outbreaks worldwide, and some non-O1 strains evolving from O1 via exchange of genes encoding cell surface polysaccharides possessed LH alleles. Analysis of polymorphisms in the gene locus implicated a high degree of genetic diversity and identical subpopulations among the V. cholerae species.

From clinical uncertainties to precision medicine: the emerging role of the gut barrier and microbiome in small bowel functional diseases

Over the last decade, remarkable progress has been made in the understanding of disease pathophysiology. Many new theories expound on the importance of emerging factors such as microbiome influences, genomics/omics, stem cells, innate intestinal immunity or mucosal barrier complexities. This has introduced a further dimension of uncertainty into clinical decision-making, but equally, may shed some light on less well-understood and difficult to manage conditions. Areas covered: Comprehensive review of the literature on gut barrier and microbiome relevant to small bowel pathology. A PubMed/Medline search from 1990 to April 2017 was undertaken and papers from this range were included. Expert commentary: The scenario of clinical uncertainty is well-illustrated by functional gastrointestinal disorders (FGIDs). The movement towards achieving a better understanding of FGIDs is expressed in the Rome IV guidelines. Novel diagnostic and therapeutic protocols focused on the GB and SB microbiome can facilitate diagnosis, management and improve our understanding of the underlying pathological mechanisms in FGIDs.

Vibrio parahaemolyticus- and V. alginolyticus-associated meningo-encephalitis in a bottlenose dolphin (Tursiops truncatus) from the Adriatic coast of Italy

A case of Vibrio parahaemolyticus- and V. alginolyticus-associated meningo-encephalitis in a bottlenose dolphin (Tursiops truncatus) found stranded along the Adriatic coast of Italy in 2016 is herein reported, along with a minireview on V. parahaemolyticus and V. alginolyticus infections in aquatic mammals. Macroscopically, two abscesses were found in the dolphin's forebrain, along with an extensive, bilateral, parasitic broncho-pneumonia. Histologically, a suppurative-to-pyogranulomatous meningo-encephalitis involved the brain but not the cerebellum. Microbiological investigations yielded isolation of V. parahaemolyticus and V. alginolyticus from the aforementioned abscesses and from the brain parenchyma, respectively, with simultaneous recovery of Shewanella algae from the heart and of Photobacterium damselae from a blowhole swab. Although V. parahaemolyticus and V. alginolyticus, which are widely distributed across marine ecosystems worldwide, likely played a role in the development of the suppurative meningo-encephalitis in this dolphin, we are not aware of previous isolations of any of these two bacteria neither from cetacean brain lesions, nor from abscesses in aquatic mammals.

Treatment with Entinostat Heals Experimental Cholera by Affecting Physical and Chemical Barrier Functions of Intestinal Epithelia

We have shown previously that oral treatment with sodium butyrate or phenylbutyrate in an experimental model of shigellosis improves clinical outcomes and induces the expression of the antimicrobial peptide CAP-18 in the large intestinal epithelia. In a subsequent study, we found that entinostat, an aroylated phenylenediamine compound, has similar therapeutic potential against shigellosis. In this study, we aimed to evaluate entinostat as a potential candidate for host-directed therapy against cholera in an experimental model. Vibrio cholerae-infected rabbits were treated with two different dose regimens of entinostat: either 0.5 mg twice daily for 2 days or 1 mg once daily for 2 days. The effects of treatment on clinical outcomes and V. cholerae shedding (CFU count in stool) were observed. Immunohistochemical analysis was carried out to assess CAP-18 expression in ileal and jejunal mucosae. The serum zonulin level was measured by an enzyme-linked immunosorbent assay (ELISA) to evaluate gut permeability. Infection of rabbits with V. cholerae downregulated CAP-18 expression in the ileal epithelium; the expression was replenished by oral treatment with entinostat at either dose regimen. The level of zonulin, a marker of gut permeability, in serum was upregulated after infection, and this upregulation was counteracted after treatment with entinostat. Entinostat treatment also led to recovery from cholera and a decline in the V. cholerae count in stool. In conclusion, the improved clinical outcome of cholera for rabbits treated with entinostat is associated with the induction of CAP-18 and the reduction of gut epithelial permeability.

The basolateral vesicle sorting machinery and basolateral proteins are recruited to the site of enteropathogenic E. coli microcolony growth at the apical membrane

Foodborne Enteropathogenic Escherichia coli (EPEC) infections of the small intestine cause diarrhea especially in children and are a major cause of childhood death in developing countries. EPEC infects the apical membrane of the epithelium of the small intestine by attaching, effacing the microvilli under the bacteria and then forming microcolonies on the cell surface. We first asked the question where on epithelial cells EPEC attaches and grows. Using models of polarized epithelial monolayers, we evaluated the sites of initial EPEC attachment to the apical membrane and found that EPEC preferentially attached over the cell-cell junctions and formed microcolonies preferentially where three cells come together at tricellular tight junctions. The ability of EPEC to adhere increased when host cell polarity was compromised yielding EPEC access to basolateral proteins. EPEC pedestals contain basolateral cytoskeletal proteins. Thus, we asked if attached EPEC causes reorganization the protein composition of the host cell plasma membrane at sites of microcolony formation. We found that EPEC microcolony growth at the apical membrane resulted in a local accumulation of basolateral plasma membrane proteins surrounding the microcolony. Basolateral marker protein aquaporin-3 localized to forming EPEC microcolonies. Components of the basolateral vesicle targeting machinery were re-routed. The Exocyst (Exo70) was recruited to individual EPEC as was the basolateral vesicle SNARE VAMP-3. Moreover, several Rab variants were also recruited to the infection site, and their dominant-negative equivalents were not. To quantitatively study the recruitment of basolateral proteins, we created a pulse of the temperature sensitive basolateral VSVG, VSVG3-SP-GFP, from the trans-Golgi Network. We found that after release from the TGN, significantly more VSVG3-SP-GFP accumulated at the site of microcolony growth than on equivalent membrane regions of uninfected cells. This suggests that trafficking of vesicles destined for the basolateral membrane are redirected to the apical site of microcolony growth. Thus, in addition to disrupting host cell fence function, local host cell plasma membrane protein composition is changed by altered protein trafficking and recruitment of basolateral proteins to the apical microcolony. This may aid EPEC attachment and subsequent microcolony growth.

Alterations in Intestinal Permeability: The Role of the "Leaky Gut" in Health and Disease

All species, including horses, suffer from alterations that increase intestinal permeability. These alterations, also known as "leaky gut," may lead to severe disease as the normal intestinal barrier becomes compromised and can no longer protect against harmful luminal contents including microbial toxins and pathogens. Leaky gut results from a variety of conditions including physical stressors, decreased blood flow to the intestine, inflammatory disease, and pathogenic infections, among others. Several testing methods exist to diagnose these alterations in both a clinical and research setting. To date, most research has focused on regulation of the host immune response due to the wide variety of factors that can potentially influence the intestinal barrier. This article serves to review the normal intestinal barrier, measurement of barrier permeability, pathogenesis and main causes of altered permeability, and highlight potential alternative therapies of leaky gut in horses while relating what has been studied in other species. Conditions resulting in barrier dysfunction and leaky gut can be a major cause of decreased performance and also death in horses. A better understanding of the intestinal barrier in disease and ways to optimize the function of this barrier is vital to the long-term health and maintenance of these animals.

Psychological stress exacerbates NSAID-induced small bowel injury by inducing changes in intestinal microbiota and permeability via glucocorticoid receptor signaling

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) are popular painkillers, but they have serious side effects, not only in the upper gastrointestinal tract but also in the small intestine. It is well known that psychological stress may exacerbate various gastrointestinal diseases. The aim of this study was to determine whether psychological stress exacerbates NSAID enteropathy and to determine the possible underlying mechanisms for this.

METHODS

Experiment 1: mice were exposed to water avoidance stress (WAS) or sham stress for 1 h per day for 8 consecutive days, and then enteropathy was induced by indomethacin. Experiment 2: cecal contents from stress (-) or (+) mice were transplanted into mice that had received antibiotics and in which NSAID enteropathy had been induced without WAS. Experiment 3: mifepristone, a glucocorticoid receptor antagonist, was injected before WAS for 8 days. Small intestinal injury, mRNA expression of TNFα, intestinal permeability, and the microbial community were assessed.

RESULTS

Psychological stress exacerbated NSAID enteropathy and increased intestinal permeability. Psychological stress induced changes in the ileal microbiota that were characterized by increases in the total number of bacteria and the proportion of Gram-negative bacteria. The increased susceptibility to NSAIDs and intestinal permeability due to WAS was transferable via cecal microbiota transplantation. The increased permeability and aggravation of NSAID enteropathy caused by WAS were blocked by the administration of mifepristone.

CONCLUSIONS

This study demonstrated a relationship between NSAID enteropathy and psychological stress, and showed the utility of studying the intestinal microbiota in order to elucidate the pathophysiology of NSAID enteropathy. It also showed the impact of stress on the intestinal microbiota and the mucosal barrier in gastrointestinal diseases.

The presence of bacteria within tissue provides insights into the pathogenesis of oral lichen planus

Oral lichen planus (OLP) is a chronic T cell-mediated mucocutaneous disease of unknown etiopathogenesis. Although various antigens have been considered, what actually triggers the inflammatory response of T cells is unknown. In the present study, we propose that intracellular bacteria present within tissues trigger T cell infiltration and provide target antigens. Sections of OLP (n = 36) and normal (n = 10) oral mucosal tissues were subjected to in situ hybridization using a universal probe targeting the bacterial 16S rRNA gene and immunohistochemistry with anti-CD3, anti-CD4, anti-CD8, and anti-macrophage-specific antibodies. Bacteria were abundant throughout the epithelium and the lamina propria of OLP tissues, which exhibited positive correlations with the levels of infiltrated CD3(+), CD4(+), and CD8(+) cells. Furthermore, bacteria were detected within the infiltrated T cells. Pyrosequencing analysis of the mucosal microbiota from OLP patients (n = 13) and control subjects (n = 11) revealed a decrease in Streptococcus and increases in gingivitis/periodontitis-associated bacteria in OLP lesions. Using the selected bacterial species, we demonstrated that certain oral bacteria damage the epithelial physical barrier, are internalized into epithelial cells or T cells, and induce production of T cell chemokines CXCL10 and CCL5. Our findings provide insights into the pathogenesis of OLP.

Vibrio cholerae hemagglutinin(HA)/protease: An extracellular metalloprotease with multiple pathogenic activities

Vibrio cholerae of serogroup O1 and O139, the etiological agent of the diarrheal disease cholera, expresses the extracellular Zn-dependent metalloprotease hemagglutinin (HA)/protease also reported as vibriolysin. This enzyme is also produced by non-O1/O139 (non-cholera) strains that cause mild, sporadic illness (i.e. gastroenteritis, wound or ear infections). Orthologs of HA/protease are present in other members of the Vibrionaceae family pathogenic to humans and fish. HA/protease belongs to the M4 neutral peptidase family and displays significant amino acid sequence homology to Pseudomonas aeruginosa elastase (LasB) and Bacillus thermoproteolyticus thermolysin. It exhibits a broad range of potentially pathogenic activities in cell culture and animal models. These activities range from the covalent modification of other toxins, the degradation of the protective mucus barrier and disruption of intestinal tight junctions. Here we review (i) the structure and regulation of HA/protease expression, (ii) its interaction with other toxins and the intestinal mucosa and (iii) discuss the possible role(s) of HA/protease in the pathogenesis of cholera.

Iron and zinc exploitation during bacterial pathogenesis

Ancient bacteria originated from metal-rich environments. Billions of years of evolution directed these tiny single cell creatures to exploit the versatile properties of metals in catalyzing chemical reactions and biological responses. The result is an entire metallome of proteins that use metal co-factors to facilitate key cellular process that range from the production of energy to the replication of DNA. Two key metals in this regard are iron and zinc, both abundant on Earth but not readily accessible in a human host. Instead, pathogenic bacteria must employ clever ways to acquire these metals. In this review we describe the many elegant ways these bacteria mine, regulate, and craft the use of two key metals (iron and zinc) to build a virulence arsenal that challenges even the most sophisticated immune response.

Gut permeability, its interaction with gut microflora and effects on metabolic health are mediated by the lymphatics system, liver and bile acid

There is evidence to link obesity (and metabolic syndrome) with alterations in gut permeability and microbiota. The underlying mechanisms have been questioned and have prompted this review. We propose that the gut barrier function is a primary driver in maintaining metabolic health with poor health being linked to ‘gut leakiness'. This review will highlight changes in intestinal permeability and how it may change gut microflora and subsequently affect metabolic health by influencing the functioning of major bodily organs/organ systems: the lymphatic system, liver and pancreas. We also discuss the likelihood that metabolic syndrome undergoes a cyclic worsening facilitated by an increase in intestinal permeability leading to gut dysbiosis, culminating in ongoing poor health leading to further exacerbated gut leakiness.

Signalling at tight junctions during epithelial differentiation and microbial pathogenesis

Tight junctions are a component of the epithelial junctional complex, and they form the paracellular diffusion barrier that enables epithelial cells to create cellular sheets that separate compartments with different compositions. The assembly and function of tight junctions are intimately linked to the actomyosin cytoskeleton and, hence, are under the control of signalling mechanisms that regulate cytoskeletal dynamics. Tight junctions not only receive signals that guide their assembly and function, but transmit information to the cell interior to regulate cell proliferation, migration and survival. As a crucial component of the epithelial barrier, they are often targeted by pathogenic viruses and bacteria, aiding infection and the development of disease. In this Commentary, we review recent progress in the understanding of the molecular signalling mechanisms that drive junction assembly and function, and the signalling processes by which tight junctions regulate cell behaviour and survival. We also discuss the way in which junctional components are exploited by pathogenic viruses and bacteria, and how this might affect junctional signalling mechanisms.

Host-pathogen interaction profiling using self-assembling human protein arrays

Host-pathogen protein interactions are fundamental to every microbial infection, yet their identification has remained challenging due to the lack of simple detection tools that avoid abundance biases while providing an open format for experimental modifications. Here, we applied the Nucleic Acid-Programmable Protein Array and a HaloTag-Halo ligand detection system to determine the interaction network of Legionella pneumophila effectors (SidM and LidA) with 10 000 unique human proteins. We identified known targets of these L. pneumophila proteins and potentially novel interaction candidates. In addition, we applied our Click chemistry-based NAPPA platform to identify the substrates for SidM, an effector with an adenylyl transferase domain that catalyzes AMPylation (adenylylation), the covalent addition of adenosine monophosphate (AMP). We confirmed a subset of the novel SidM and LidA targets in independent in vitro pull-down and in vivo cell-based assays, and provided further insight into how these effectors may discriminate between different host Rab GTPases. Our method circumvents the purification of thousands of human and pathogen proteins, and does not require antibodies against or prelabeling of query proteins. This system is amenable to high-throughput analysis of effectors from a wide variety of human pathogens that may bind to and/or post-translationally modify targets within the human proteome.

How bacterial pathogens colonize their hosts and invade deeper tissues

Bacterial pathogens have evolved a wide range of strategies to colonize and invade human organs, despite the presence of multiple host defense mechanisms. In this review, we will describe how pathogenic bacteria can adhere and multiply at the surface of host cells, how some bacteria can enter and proliferate inside these cells, and finally how pathogens may cross epithelial or endothelial host barriers and get access to internal tissues, leading to severe diseases in humans.

Non-O1/non-O139 Vibrio cholerae carrying multiple virulence factors and V. cholerae O1 in the Chesapeake Bay, Maryland

Non-O1/non-O139 Vibrio cholerae inhabits estuarine and coastal waters globally, but its clinical significance has not been sufficiently investigated, despite the fact that it has been associated with septicemia and gastroenteritis. The emergence of virulent non-O1/non-O139 V. cholerae is consistent with the recognition of new pathogenic variants worldwide. Oyster, sediment, and water samples were collected during a vibrio surveillance program carried out from 2009 to 2012 in the Chesapeake Bay, Maryland. V. cholerae O1 was detected by a direct fluorescent-antibody (DFA) assay but was not successfully cultured, whereas 395 isolates of non-O1/non-O139 V. cholerae were confirmed by multiplex PCR and serology. Only a few of the non-O1/non-O139 V. cholerae isolates were resistant to ampicillin and/or penicillin. Most of the isolates were sensitive to all antibiotics tested, and 77 to 90% carried the El Tor variant hemolysin gene hlyAET, the actin cross-linking repeats in toxin gene rtxA, the hemagglutinin protease gene hap, and the type 6 secretion system. About 19 to 21% of the isolates carried the neuraminidase-encoding gene nanH and/or the heat-stable toxin (NAG-ST), and only 5% contained a type 3 secretion system. None of the non-O1/non-O139 V. cholerae isolates contained Vibrio pathogenicity island-associated genes. However, ctxA, ace, or zot was present in nine isolates. Fifty-five different genotypes showed up to 12 virulence factors, independent of the source of isolation, and represent the first report of both antibiotic susceptibility and virulence associated with non-O1/non-O139 V. cholerae from the Chesapeake Bay. Since these results confirm the presence of potentially pathogenic non-O1/non-O139 V. cholerae, monitoring for total V. cholerae, regardless of serotype, should be done within the context of public health.

The tyrosine kinase BceF and the phosphotyrosine phosphatase BceD of Burkholderia contaminans are required for efficient invasion and epithelial disruption of a cystic fibrosis lung epithelial cell line

Bacterial tyrosine kinases and their cognate protein tyrosine phosphatases are best known for regulating the biosynthesis of polysaccharides. Moreover, their roles in the stress response, DNA metabolism, cell division, and virulence have also been documented. The aim of this study was to investigate the pathogenicity and potential mechanisms of virulence dependent on the tyrosine kinase BceF and phosphotyrosine phosphatase BceD of the cystic fibrosis opportunistic pathogen Burkholderia contaminans IST408. The insertion mutants bceD::Tp and bceF::Tp showed similar attenuation of adhesion and invasion of the cystic fibrosis lung epithelial cell line CFBE41o- compared to the parental strain B. contaminans IST408. In the absence of bceD or bceF genes, B. contaminans also showed a reduction in the ability to translocate across polarized epithelial cell monolayers, demonstrated by a higher transepithelial electrical resistance, reduced flux of fluorescein isothiocyanate-labeled bovine serum albumin, and higher levels of tight junction proteins ZO-1, occludin, and claudin-1 present in monolayers exposed to these bacterial mutants. Furthermore, bceD::Tp and bceF::Tp mutants induced lower levels of interleukin-6 (IL-6) and IL-8 release than the parental strain. In conclusion, although the mechanisms of pathogenicity dependent on BceD and BceF are not understood, these proteins contribute to the virulence of Burkholderia by enhancement of cell attachment and invasion, disruption of epithelial integrity, and modulation of the proinflammatory response.

Klebsiella pneumoniae translocates across the intestinal epithelium via Rho GTPase- and phosphatidylinositol 3-kinase/Akt-dependent cell invasion

Klebsiella pneumoniae is an important pathogen that causes hospital-acquired septicemia and is associated with the recent emergence of community-acquired pyogenic liver abscess (PLA). Clinical typing suggests that K. pneumoniae infections originate from the gastrointestinal reservoir. However, the underlying mechanism remains unknown. Here, we have sought to determine how K. pneumoniae penetrates the intestinal barrier. We identified that bacteremia and PLA clinical isolates adhered to and invaded intestinal epithelial cells. Internalization of K. pneumoniae in three different human colonic cell lines was visualized by confocal microscopy and three-dimensional (3D) imaging. Using a Transwell system, we demonstrated that these K. pneumoniae isolates translocated across a polarized Caco-2 monolayer. No disruptions of transepithelial electrical resistance and altered distribution of tight junction protein ZO-1 or occludin were observed. Therefore, K. pneumoniae appeared to penetrate the intestinal epithelium via a transcellular pathway. Using specific inhibitors, we characterized the host signaling pathways involved. Inhibition by cytochalasin D and nocodazole suggested that actin and microtubule cytoskeleton were both important for K. pneumoniae invasion. A Rho inhibitor, ML141, LY294002, and an Akt1/2 inhibitor diminished K. pneumoniae invasion in a dose-dependent manner, indicating that Rho family GTPases and phosphatidylinositol 3-kinase (PI3K)/Akt signaling were required. By a mouse model of gastrointestinal colonization, in vivo invasion of K. pneumoniae into colonic epithelial cells was demonstrated. Our results present evidence to describe a possible mechanism of gastrointestinal translocation for K. pneumoniae. Cell invasion by manipulating host machinery provides a pathway for gut-colonized K. pneumoniae cells to penetrate the intestinal barrier and access extraintestinal locations to cause disease.

Intestinal permeability--a new target for disease prevention and therapy

Data are accumulating that emphasize the important role of the intestinal barrier and intestinal permeability for health and disease. However, these terms are poorly defined, their assessment is a matter of debate, and their clinical significance is not clearly established. In the present review, current knowledge on mucosal barrier and its role in disease prevention and therapy is summarized. First, the relevant terms 'intestinal barrier' and 'intestinal permeability' are defined. Secondly, the key element of the intestinal barrier affecting permeability are described. This barrier represents a huge mucosal surface, where billions of bacteria face the largest immune system of our body. On the one hand, an intact intestinal barrier protects the human organism against invasion of microorganisms and toxins, on the other hand, this barrier must be open to absorb essential fluids and nutrients. Such opposing goals are achieved by a complex anatomical and functional structure the intestinal barrier consists of, the functional status of which is described by 'intestinal permeability'. Third, the regulation of intestinal permeability by diet and bacteria is depicted. In particular, potential barrier disruptors such as hypoperfusion of the gut, infections and toxins, but also selected over-dosed nutrients, drugs, and other lifestyle factors have to be considered. In the fourth part, the means to assess intestinal permeability are presented and critically discussed. The means vary enormously and probably assess different functional components of the barrier. The barrier assessments are further hindered by the natural variability of this functional entity depending on species and genes as well as on diet and other environmental factors. In the final part, we discuss selected diseases associated with increased intestinal permeability such as critically illness, inflammatory bowel diseases, celiac disease, food allergy, irritable bowel syndrome, and--more recently recognized--obesity and metabolic diseases. All these diseases are characterized by inflammation that might be triggered by the translocation of luminal components into the host. In summary, intestinal permeability, which is a feature of intestinal barrier function, is increasingly recognized as being of relevance for health and disease, and therefore, this topic warrants more attention.

Intestinal barrier function and the brain-gut axis

The luminal-mucosal interface of the intestinal tract is the first relevant location where microorganism-derived antigens and all other potentially immunogenic particles face the scrutiny of the powerful mammalian immune system. Upon regular functioning conditions, the intestinal barrier is able to effectively prevent most environmental and external antigens to interact openly with the numerous and versatile elements that compose the mucosal-associated immune system. This evolutionary super system is capable of processing an astonishing amount of antigens and non-immunogenic particles, approximately 100 tons in one individual lifetime, only considering food-derived components. Most important, to develop oral tolerance and proper active immune responses needed to prevent disease and inflammation, this giant immunogenic load has to be managed in a way that physiological inflammatory balance is constantly preserved. Adequate functioning of the intestinal barrier involves local and distant regulatory networks integrating the so-called brain-gut axis. Along this complex axis both brain and gut structures participate in the processing and execution of response signals to external and internal changes coming from the digestive tract, using multidirectional pathways to communicate. Dysfunction of brain-gut axis facilitates malfunctioning of the intestinal barrier, and vice versa, increasing the risk of uncontrolled immunological reactions that may trigger mucosal and brain low-grade inflammation, a putative first step to the initiation of more permanent gut disorders. In this chapter, we describe the structure, function and interactions of intestinal barrier, microbiota and brain-gut axis in both healthy and pathological conditions.

Immunohistological characterization of intercellular junction proteins in rhesus macaque intestine

Epithelial junctions play an important role in regulating paracellular permeability and intercellular adhesion. It has been reported that changes in the density of epithelial junctions and/or distribution pattern can contribute to various gastrointestinal (GI) disorders. In this study, we investigated the distribution of the tight junction (Claudins. 1, 3, 4, 5, 7, 10, Zonula Occludens (ZO-1), Occludin), adherens junction (E-cadherin), desmosome (Desmoglein 2, Desmocollin 2) and gap junction (Connexin 43) proteins in the jejunum, ileum and colonic epithelium of healthy rhesus macaques (RM) using immunofluorescence labeling. While proteins in these respective junctions were expressed throughout the jejunum, ileum and colon of RM, we observed differential labeling in epithelial cells from these sites. Claudins 1, 3, 4, 7, E-cadherin and Desmoglein 2 were distributed in the respective intercellular junctions with additional labeling in the lateral membrane of epithelial cells in both small and large intestine. However, claudin 5, claudin 10, ZO-1 and occludin showed uniform distribution in the intercellular junctions of crypt and surface epithelial cells of the intestine. Desmocollin 2 localized predominantly in the upper two thirds along the lateral membrane while desmoglein 2 was distributed along the entire lateral membrane of intestinal epithelial cells. In contrast, connexin 43 exhibited punctate lateral labeling in crypt epithelial cells of the small and large intestine. Our results show diverse localization of epithelial intercellular junction proteins along the intestinal tract of RM. These findings may correlate with differences in paracellular permeability and adhesion along the intestinal tract and could correlate with pathologic disease in these regions of the intestine.

Cleavage of transmembrane junction proteins and their role in regulating epithelial homeostasis

Epithelial tissues form a selective barrier that separates the external environment from the internal tissue milieu. Single epithelial cells are densely packed and associate via distinct intercellular junctions. Intercellular junction proteins not only control barrier properties of the epithelium but also play an important role in regulating epithelial homeostasis that encompasses cell proliferation, migration, differentiation and regulated shedding. Recent studies have revealed that several proteases target epithelial junction proteins during physiological maturation as well as in pathologic states such as inflammation and cancer. This review discusses mechanisms and biological consequences of transmembrane junction protein cleavage. The influence of junction protein cleavage products on pathogenesis of inflammation and cancer is discussed.