Proteolytic activity of the Bacteroides fragilis enterotoxin causes fluid secretion and intestinal damage in vivo

Nontoxigenic Bacteroides fragilis: A double-edged sword

The contribution of commensal microbes to human health and disease is unknown. Bacteroides fragilis (B. fragilis) is an opportunistic pathogen and a common colonizer of the human gut. Nontoxigenic B. fragilis (NTBF) and enterotoxigenic B. fragilis (ETBF) are two kinds of B. fragilis. NTBF has been shown to affect the host immune system and interact with gut microbes and pathogenic microbes. Previous studies indicated that certain strains of B. fragilis have the potential to serve as probiotics, based on their observed relationship with the immune system. However, several recent studies have shown detrimental effects on the host when beneficial gut bacteria are found in the digestive system or elsewhere. In some pathological conditions, NTBF may have adverse reactions. This paper presents a comprehensive analysis of NTBF ecology from the host-microbe perspective, encompassing molecular disease mechanisms analysis, bacteria-bacteria interaction, bacteria-host interaction, and the intricate ecological context of the gut. Our review provides much-needed insights into the precise application of NTBF.

Dissecting Gut-Microbial Community Interactions using a Gut Microbiome-on-a-Chip

While the human gut microbiota has a significant impact on gut health and disease, understanding of the roles of gut microbes, interactions, and collective impact of gut microbes on various aspects of human gut health is limited by the lack of suitable in vitro model system that can accurately replicate gut-like environment and enable the close visualization on causal and mechanistic relationships between microbial constitutents and the gut. , In this study, we present a scalable Gut Microbiome-on-a-Chip (GMoC) with great imaging capability and scalability, providing a physiologically relevant dynamic gut-microbes interfaces. This chip features a reproducible 3D stratified gut epithelium derived from Caco-2 cells (µGut), mimicking key intestinal architecture, functions, and cellular complexity, providing a physiolocially relevant gut environment for microbes residing in the gut. Incorporating tumorigenic bacteria, enterotoxigenic Bacteroides fragilis (ETBF), into the GMoC enable the observation of pathogenic behaviors of ETBF, leading to µGut disruption and pro-tumorigenic signaling activations. Pre-treating the µGut with a beneficial gut microbe Lactobacillus spp., effectively prevent ETBF-mediated gut pathogenesis, preserving the healthy state of the µGut through competition-mediated colonization resistance. The GMoC holds potential as a valuable tool for exploring unknown roles of gut microbes in microbe-induced pathogenesis and microbe-based therapeutic development.

A new strategy for treating colorectal cancer: Regulating the influence of intestinal flora and oncolytic virus on interferon

Colorectal cancer (CRC) has the third highest incidence and the second highest mortality in the world, which seriously affects human health, while current treatments methods for CRC, including systemic therapy, preoperative radiotherapy, and surgical local excision, still have poor survival rates for patients with metastatic disease, making it critical to develop new strategies for treating CRC. In this article, we found that the gut microbiota can modulate the signaling pathways of cancer cells through direct contact with tumor cells, generate inflammatory responses and oxidative stress through interactions between the innate and adaptive immune systems, and produce diverse metabolic combinations to trigger specific immune responses and promote the initiation of systemic type I interferon (IFN-I) and anti-viral immunity. In addition, oncolytic virus-mediated immunotherapy for regulating oncolytic virus can directly lyse tumor cells, induce the immune activity of the body, interact with interferon, inhibit the anti-viral effect of IFN-I, and enhance the anti-tumor effect of IFN-II. Interferon plays an important role in the anti-tumor process. We put forward that exploring the effects of intestinal flora and oncolytic virus on interferon to treat CRC is a promising therapeutic option.

The gut microbiota of people with asthma influences lung inflammation in gnotobiotic mice

The gut microbiota in early childhood is linked to asthma risk, but may continue to affect older patients with asthma. Here, we profile the gut microbiota of 38 children (19 asthma, median age 8) and 57 adults (17 asthma, median age 28) by 16S rRNA sequencing and find individuals with asthma harbored compositional differences from healthy controls in both adults and children. We develop a model to aid the design of mechanistic experiments in gnotobiotic mice and show enterotoxigenic Bacteroides fragilis (ETBF) is more prevalent in the gut microbiota of patients with asthma compared to healthy controls. In mice, ETBF, modulated by community context, can increase oxidative stress in the lungs during allergic airway inflammation (AAI). Our results provide evidence that ETBF affects the phenotype of airway inflammation in a subset of patients with asthma which suggests that therapies targeting the gut microbiota may be helpful tools for asthma control.

Interaction between microbiota and immunity and its implication in colorectal cancer

Colorectal cancer (CRC) is one of the leading causes of cancer-related death in the world. Besides genetic causes, colonic inflammation is one of the major risk factors for CRC development, which is synergistically regulated by multiple components, including innate and adaptive immune cells, cytokine signaling, and microbiota. The complex interaction between CRC and the gut microbiome has emerged as an important area of current CRC research. Metagenomic profiling has identified a number of prominent CRC-associated bacteria that are enriched in CRC patients, linking the microbiota composition to colitis and cancer development. Some microbiota species have been reported to promote colitis and CRC development in preclinical models, while a few others are identified as immune modulators to induce potent protective immunity against colitis and CRC. Mechanistically, microbiota regulates the activation of different immune cell populations, inflammation, and CRC via crosstalk between innate and adaptive immune signaling pathways, including nuclear factor kappa B (NF-κB), type I interferon, and inflammasome. In this review, we provide an overview of the potential interactions between gut microbiota and host immunity and how their crosstalk could synergistically regulate inflammation and CRC, thus highlighting the potential roles and mechanisms of gut microbiota in the development of microbiota-based therapies to prevent or alleviate colitis and CRC.

Multi-omics analyses of the ulcerative colitis gut microbiome link Bacteroides vulgatus proteases with disease severity

Ulcerative colitis (UC) is driven by disruptions in host-microbiota homoeostasis, but current treatments exclusively target host inflammatory pathways. To understand how host-microbiota interactions become disrupted in UC, we collected and analysed six faecal- or serum-based omic datasets (metaproteomic, metabolomic, metagenomic, metapeptidomic and amplicon sequencing profiles of faecal samples and proteomic profiles of serum samples) from 40 UC patients at a single inflammatory bowel disease centre, as well as various clinical, endoscopic and histologic measures of disease activity. A validation cohort of 210 samples (73 UC, 117 Crohn's disease, 20 healthy controls) was collected and analysed separately and independently. Data integration across both cohorts showed that a subset of the clinically active UC patients had an overabundance of proteases that originated from the bacterium Bacteroides vulgatus. To test whether B. vulgatus proteases contribute to UC disease activity, we first profiled B. vulgatus proteases found in patients and bacterial cultures. Use of a broad-spectrum protease inhibitor improved B. vulgatus-induced barrier dysfunction in vitro, and prevented colitis in B. vulgatus monocolonized, IL10-deficient mice. Furthermore, transplantation of faeces from UC patients with a high abundance of B. vulgatus proteases into germfree mice induced colitis dependent on protease activity. These results, stemming from a multi-omics approach, improve understanding of functional microbiota alterations that drive UC and provide a resource for identifying other pathways that could be inhibited as a strategy to treat this disease.

Evaluation of the Effects of Different Bacteroides vulgatus Strains against DSS-Induced Colitis

Although the strain-dependent effects of Bacteroides vulgatus on alleviating intestinal inflammatory diseases have been demonstrated, the literature has rarely focused on the underlying causes of this effect. In this study, we selected four B. vulgatus strains (FTJS5K1, FTJS7K1, FSDTA11B14, and FSDLZ51K1) with different genomic characteristics and evaluated their protective roles against dextran sulfate sodium- (DSS-) induced colitis. Compared to the other three tested strains, B. vulgatus 7K1 more strongly ameliorated the DSS-induced weight loss, shortening of the colon length, increased disease activity index scores, colonic tissue injury, and immunomodulatory disorder. In contrast, B. vulgatus 51K1 significantly worsened the DSS-induced alterations in the tumor necrosis factor-alpha (TNF-α) concentration and colonic histopathology. A comparative genomic analysis of B. vulgatus 7K1 and 51K1 showed that the beneficial effects of B. vulgatus 7K1 may be associated with some of its specific genes involved in the production of short-chain fatty acids or capsular polysaccharides and enhancement of its survivability in the gut. In conclusion, these findings indicate that the supplementation of B. vulgatus 7K1 is a potentially efficacious intervention for alleviating colitis and provides scientific support for the screening of probiotics with anticolitis effect.

Microbiome in Colorectal Cancer: How to Get from Meta-omics to Mechanism?

Mounting evidence from metagenomic analyses suggests that a state of pathological microbial imbalance or dysbiosis is prevalent in the gut of patients with colorectal cancer. Several bacterial taxa have been identified of which representative isolate cultures interact with human cancer cells in vitro and trigger disease pathways in animal models. However, how the complex interrelationships in dysbiotic communities may be involved in cancer pathogenesis remains a crucial question. Here, we provide a survey of current knowledge of the gut microbiome in colorectal cancer. Moving beyond observational studies, we outline new experimental approaches for gaining ecosystem-level mechanistic understanding of the gut microbiome's role in cancer pathogenesis.

Wnt/β-Catenin Signaling as a Molecular Target by Pathogenic Bacteria

The Wnt/β-catenin signaling pathway is crucial to regulate cell proliferation and polarity, cell determination, and tissue homeostasis. The activation of Wnt/β-catenin signaling is based on the interaction between Wnt glycoproteins and seven transmembrane receptors-Frizzled (Fzd). This binding promotes recruitment of the scaffolding protein Disheveled (Dvl), which results in the phosphorylation of the co-receptor LRP5/6. The resultant molecular complex Wnt-Fzd-LRP5/6-Dvl forms a structural region for Axin interaction that disrupts Axin-mediated phosphorylation/degradation of the transcriptional co-activator β-catenin, thereby allowing it to stabilize and accumulate in the nucleus where it activates the expression of Wnt-dependent genes. Due to the prominent physiological function, the Wnt/β-catenin signaling must be strictly controlled because its dysregulation, which is caused by different stimuli, may lead to alterations in cell proliferation, apoptosis, and inflammation-associated cancer. The virulence factors from pathogenic bacteria such as Salmonella enterica sv Typhimurium, Helicobacter pylori, Mycobacterium tuberculosis, Pseudomonas aeruginosa, Citrobacter rodentium, Clostridium difficile, Bacteroides fragilis, Escherichia coli, Haemophilus parasuis, Lawsonia intracellularis, Shigella dysenteriae, and Staphylococcus epidermidis employ a variety of molecular strategies to alter the appropriate functioning of diverse signaling pathways. Among these, Wnt/β-catenin has recently emerged as an important target of several virulence factors produced by bacteria. The mechanisms used by these factors to interfere with the activity of Wnt/β-catenin is diverse and include the repression of Wnt inhibitors' expression by the epigenetic modification of histones, blocking Wnt-Fzd ligand binding, activation or inhibition of β-catenin nuclear translocation, down- or up-regulation of Wnt family members, and inhibition of Axin-1 expression that promotes β-catenin activity. Such a variety of mechanisms illustrate an evolutionary co-adaptation of eukaryotic molecular signaling to a battery of soluble or structural components synthesized by pathogenic bacteria. This review gathers the recent efforts to elucidate the mechanistic details through which bacterial virulence factors modulate Wnt/β-catenin signaling and its physiological consequences concerning the inflammatory response and cancer.

Detection of the Bacteroides fragilis toxin gene in sheep with and without small intestinal adenocarcinoma

Aims: To determine if presence of the Bacteroides fragilis toxin (bft) gene, a molecular marker of colonic carriage of entertoxigenic Bacteroides fragilis (ETBF) in humans, was associated with a finding of small intestinal adenocarcinomas (SIA) in sheep in New Zealand. Methods: Samples of jejunal tissue were collected from the site of tumours and from grossly normal adjacent tissue in 20 sheep, in different consignments, diagnosed with SIA based on gross examination of viscera following slaughter. Two jejunal samples were also collected from a control sheep in the same consignment that had no gross evidence of SIA. A PCR assay was used to detect the presence of the bft gene in the samples. Results: Of the sheep with SIA, the bft gene was amplified from one or both samples from 7/20 (35%) sheep, and in sheep that had no gross evidence of SIA the bft gene was amplified from at least one sample in 11/20 (55%) sheep (RR 0.61; 95% CI = 0.30-1.25; p = 0.34). Of 11 positive samples analysed, ETBF subtype bft-1 was detected in one, bft-2 was detected in 10, and none were bft-3. Conclusions and Clinical Relevance: There was a high prevalence of detection of the bft gene in both SIA-affected and non-affected sheep, but there was no apparent association between carriage of ETBF, evidenced by detection of the bft gene, and the presence of SIA. ETBF are increasingly implicated in the aetiology of human colorectal cancer, raising the possibility that sheep may provide a zoonotic reservoir of this potentially carcinogenic bacterium. Abbreviation: Bft: Bacteroides fragilis toxin; ETBF: Enterotoxigenic Bacteroides fragilis; SIA: Small intestinal adenocarcinoma.

Mycobacterium tuberculosis Zinc Metalloprotease-1 Assists Mycobacterial Dissemination in Zebrafish

Zinc metalloprotease-1 (Zmp1) from Mycobacterium tuberculosis (M.tb), the tuberculosis (TB) causing bacillus, is a virulence factor involved in inflammasome inactivation and phagosome maturation arrest. We earlier reported that Zmp1 was secreted under granuloma-like stress conditions, induced Th2 cytokine microenvironment and was highly immunogenic in TB patients as evident from high anti-Zmp1 antibody titers in their sera. In this study, we deciphered a new physiological role of Zmp1 in mycobacterial dissemination. Exogenous treatment of THP-1 cells with 500 nM and 1 μM of recombinant Zmp1 (rZmp1) resulted in necrotic cell death. Apart from inducing secretion of necrotic cytokines, TNFα, IL-6, and IL-1β, it also induced the release of chemotactic chemokines, MCP-1, MIP-1β, and IL-8, suggesting its likely function in cell migration and mycobacterial dissemination. This was confirmed by Gap closure and Boyden chamber assays, where Zmp1 treated CHO or THP-1 cells showed ∼2 fold increased cell migration compared to the untreated cells. Additionally, Zebrafish-M. marinum based host–pathogen model was used to study mycobacterial dissemination in vivo. Td-Tomato labeled M. marinum (TdM. marinum) when injected with rZmp1 showed increased dissemination to tail region from the site of injection as compared to the untreated control fish in a dose-dependent manner. Summing up these observations along with the earlier reports, we propose that Zmp1, a multi-faceted protein, when released by mycobacteria in granuloma, may lead to necrotic cell damage and release of chemotactic chemokines by surrounding infected macrophages, attracting new immune cells, which in turn may lead to fresh cellular infections, thus assisting mycobacterial dissemination.

Peptide Sequence Region That is Essential for the Interactions of the Enterotoxigenic Bacteroides fragilis Metalloproteinase II with E-cadherin

Bacteroides fragilis is a valuable anaerobic commensal and an essential component of the gut microbiome in humans. The presence of a short pathogenicity island in the genome is predominantly associated with the enterotoxigenic strains of B. fragilis. Metallopro-teinase II (MPII) and fragilysin (FRA) are the structurally related enzymes encoded by the pathogenicity island in the enterotoxigenic strains. Accordingly, there is a significant overlap between the cleavage preferences of MPII and FRA. These proteinases, however, are counter-transcribed in the bacterial genome suggesting their distinct and specialized functions in the course of infection. It is well established that FRA directly cleaves E-cadherin, a key protein of the cell-to-cell adhesion junctions in the intestinal epithelium. Counterintuitively, MPII directly binds to, rather than cleaves, E-cadherin. Structural modeling suggested that a potential E-cadherin binding site involves the C-terminal -helical region of the MPII catalytic domain. The sequence of this region is different in MPII and FRA. Here, we employed substitution mutagenesis of this C-terminal -helical region to isolate the MPII mutants with the potentially inactivated E-cadherin binding site. Overall, as a result of our modeling, mutagenesis and binding studies, we determined that the C-terminal ten residue segment is essential for the binding of MPII, but not of FRA3, to E-cadherin, and that the resulting MPII•E-cadherin complex does not impair E-cadherin-dependent cell-to-cell contacts. It is possible to envision that the putative cleavage targets of MPII should be explored not only on the host cell surface but also in B. fragilis.

Distinct interactions with cellular E-cadherin of the two virulent metalloproteinases encoded by a Bacteroides fragilis pathogenicity island

Bacteroides fragilis causes the majority of Gram-negative anaerobic infections in the humans. The presence of a short, 6-kb, pathogenicity island in the genome is linked to enterotoxigenic B. fragilis (ETBF). The role of the enterotoxin in B. fragilis virulence, however, remains to be determined, as the majority of clinical isolates lack ETBF genes and healthy individuals carry enterotoxin-positive B. fragilis. The island encodes secretory metalloproteinase II (MPII) and one of three homologous enterotoxigenic fragilysin isoenzymes (FRA; also termed B. fragilis toxin or BFT). The secretory metalloproteinases expressed from the genes on the B. fragilis pathogenicity island may have pathological importance within the gut, not linked to diarrhea. MPII and FRA are counter-transcribed in the bacterial genome, implying that regardless of their structural similarity and overlapping cleavage preferences these proteases perform distinct and highly specialized functions in the course of B. fragilis infection. The earlier data by us and others have demonstrated that FRA cleaves cellular E-cadherin, an important adherens junction protein, and weakens cell-to-cell contacts. Using E-cadherin-positive and E-cadherin-deficient cancer cells, and the immunostaining, direct cell binding and pull-down approaches, we, however, demonstrated that MPII via its catalytic domain efficiently binds, rather than cleaves, E-cadherin. According to our results, E-cadherin is an adherens junction cellular receptor, rather than a proteolytic target, of the B. fragilis secretory MPII enzyme. As a result of the combined FRA and MPII proteolysis, cell-to-cell contacts and adherens junctions are likely to weaken further.

Bacteroides fragilis subverts mucosal biology: from symbiont to colon carcinogenesis

The human body comprises fewer host cells than bacterial cells, most of which are obligate anaerobes residing in the gut. The symbiont Bacteroides fragilis constitutes a relatively small proportion (up to 1%-2%) of cultured fecal bacteria, but colonizes most humans. There are 2 classes of B. fragilis distinguished by their ability to secrete a zinc-dependent metalloprotease toxin, B. fragilis toxin (BFT). Strains that do not secrete BFT are nontoxigenic B. fragilis (NTBF), and those that do are called enterotoxigenic B. fragilis (ETBF). ETBF can induce clinical pathology, including inflammatory diarrhea, although asymptomatic colonization may be common. Intestinal inflammation is mediated by BFT, as yet the only known virulence factor of ETBF. Recent experimental evidence demonstrating that ETBF-driven colitis promotes colon tumorigenesis has generated interest in the potential contribution of ETBF to human colon carcinogenesis. Critical questions about the epidemiology of chronic, subclinical human colonization with ETBF and its impact on the biology of the colon need to be addressed.

Structural and functional diversity of metalloproteinases encoded by the Bacteroides fragilis pathogenicity island

Bacteroides fragilis causes the majority of anaerobic infections in humans. The presence of a pathogenicity island in the genome discriminates pathogenic and commensal B. fragilis strains. The island encodes metalloproteinase II (MPII), a potential virulence protein, and one of three homologous fragilysin isozymes (FRA; also termed B. fragilis toxin or BFT). Here, we report biochemical data on the structural-functional characteristics of the B. fragilis pathogenicity island proteases by reporting the crystal structure of MPII at 2.13 Å resolution, combined with detailed characterization of the cleavage preferences of MPII and FRA3 (as a representative of the FRA isoforms), identified using a high-throughput peptide cleavage assay with 18 583 substrate peptides. We suggest that the evolution of the MPII catalytic domain can be traced to human and archaebacterial proteinases, whereas the prodomain fold is a feature specific to MPII and FRA. We conclude that the catalytic domain of both MPII and FRA3 evolved differently relative to the prodomain, and that the prodomain evolved specifically to fit the B. fragilis pathogenicity. Overall, our data provide insights into the evolution of cleavage specificity and activation mechanisms in the virulent metalloproteinases.

Enterotoxigenic Bacteroides fragilis

Bacteroides fragilis is a minor component of the microbial flora of the intestine but the most frequent disease--causing anaerobe. Virulence characteristics are its capsule, which induces abscess formation, and the production of fragilysin, a Zn-metalloprotease. This toxin's action is to hydrolyze the extracellular domain of E-cadherin, the effect of which is to disrupt intercellular adhesion and thus increase permeability of the epithelium, causing intracellular redistribution of actin with morphologic changes to the cells and release of beta-catenin, which translocates to the nucleus and ultimately increases cellular proliferation. Clinically, enterotoxigenic B. fragilis is linked to secretory diarrhea, particularly in children. Preliminary evidence suggests that enterotoxigenic B. fragilis may also be linked to inflammatory bowel disease and colon cancer.

Enterotoxigenic Bacteroides fragilis: a rogue among symbiotes

Enterotoxigenic Bacteroides fragilis (ETBF) strains are strains of B. fragilis that secrete a 20-kDa heat-labile zinc-dependent metalloprotease toxin termed the B. fragilis toxin (BFT). BFT is the only recognized virulence factor specific for ETBF. ETBF strains are associated with inflammatory diarrheal disease in children older than 1 year of age and in adults; limited data suggest an association of ETBF colonization with inflammatory bowel disease flare-ups and colorectal cancer. ETBF secretes one of three highly related BFT isoforms. The relationship between BFT isoform and disease expression is unknown. Although the mechanism of action of BFT is incompletely understood, available data suggest that BFT binds to a specific intestinal epithelial cell receptor, stimulating intestinal cell signal transduction pathways that result in cell morphology changes, cleavage of E-cadherin, reduced colonic barrier function, and increased epithelial cell proliferation and cytokine expression (such as the proinflammatory chemokine interleukin-8). Together, the data suggest that in some hosts, ETBF acts via secretion of BFT to induce colitis. However, the full spectrum of clinical disease related to ETBF and the impact of chronic ETBF colonization on the host remain to be defined.

Association of enterotoxigenic Bacteroides fragilis infection with inflammatory diarrhea

BACKGROUND

Diarrheal illnesses remain a leading cause of morbidity and mortality globally, with increasing recognition of long-term sequelae, including postinfectious irritable bowel syndrome and growth faltering, as well as cognitive deficits in children. Identification of specific etiologic agents is often lacking. In vitro and in vivo data suggest that enterotoxigenic Bacteroides fragilis (ETBF) may contribute to the burden of colonic inflammatory diarrheal disease. The study goal was to investigate the pathogenesis of ETBF diarrheal illnesses.

METHODS

We performed an observational study of children and adults with acute diarrheal illnesses in Dhaka, Bangladesh, from January 2004 through November 2005, to define the clinical presentation, intestinal inflammatory responses, and systemic and intestinal antibody responses to ETBF. Other enteric pathogens were also evaluated.

RESULTS

ETBF was identified to cause a clinical syndrome with marked abdominal pain and nonfebrile inflammatory diarrhea in both children (age, >1 year) and adults. Fecal leukocytes, lactoferrin, and proinflammatory cytokines (interleukin 8, tumor necrosis factor-alpha)-as well as B. fragilis toxin systemic antitoxin responses-increased rapidly in ETBF-infected patients. Evidence of intestinal inflammation often persisted for at least 3 weeks, despite antibiotic therapy.

CONCLUSIONS

ETBF infection is a newly recognized cause of inflammatory diarrhea in children and adults. Future studies are needed to evaluate the role of ETBF in persistent colonic inflammation and other morbid sequelae of acute diarrheal disease.

Induction of persistent colitis by a human commensal, enterotoxigenic Bacteroides fragilis, in wild-type C57BL/6 mice

Enterotoxigenic Bacteroides fragilis (ETBF) causes diarrhea and is implicated in inflammatory bowel diseases and colorectal cancer. The only known ETBF virulence factor is the Bacteroides fragilis toxin (BFT), which induces E-cadherin cleavage, interleukin-8 secretion, and epithelial cell proliferation. A murine model for ETBF has not been characterized. Specific pathogen-free (SPF) C57BL/6J or germfree 129S6/SvEv mice were orally inoculated with wild-type ETBF (WT-ETBF) strains, a nontoxigenic WT strain of B. fragilis (WT-NTBF), WT-NTBF overexpressing bft (rETBF), or WT-NTBF overexpressing a biologically inactive mutated bft (rNTBF). In SPF and germfree mice, ETBF caused colitis but was lethal only in germfree mice. Colonic histopathology demonstrated mucosal thickening with inflammatory cell infiltration, crypt abscesses, and epithelial cell exfoliation, erosion, and ulceration. SPF mice colonized with rETBF mimicked WT-ETBF, whereas rNTBF caused no histopathology. Intestinal epithelial E-cadherin was rapidly cleaved in vivo in WT-ETBF-colonized mice and in vitro in intestinal tissues cultured with purified BFT. ETBF mice colonized for 16 months exhibited persistent colitis. BFT did not directly induce lymphocyte proliferation, dendritic cell stimulation, or Toll-like receptor activation. In conclusion, WT-ETBF induced acute then persistent colitis in SPF mice and rapidly lethal colitis in WT germfree mice. Our data support the hypothesis that chronic colonization with the human commensal ETBF can induce persistent, subclinical colitis in humans.

Inhibition of apoptosis in Bacteroides fragilis enterotoxin-stimulated intestinal epithelial cells through the induction of c-IAP-2

Enterotoxigenic Bacteroides fragilis produces an approximately 20-kDa heat-labile enterotoxin (BFT) that plays an essential role in generating mucosal inflammation. Although it is well known that proinflammatory signals are expressed in BFT-stimulated intestinal epithelial cells, cell death processes have not been elucidated. BFT induced apoptosis in HT-29 cells, but the apoptosis was first apparent 36 h after stimulation. During the early period of BFT stimulation, expression of cellular inhibitor of apoptosis protein-2 (c-IAP2) increased, and inhibition of c-IAP2 augmented the apoptotic cell death. Inhibition of BFT-induced COX-2 expression decreased prostaglandin E(2) (PGE(2)) production, which led not only to a decrease of c-IAP2 activity but also to an enhancement of DNA fragmentation in the early period of BFT stimulation. Furthermore, apoptosis inhibition through PGE(2) and c-IAP2 was mainly regulated by a p38 mitogen-activated protein kinase (MAPK). These results suggest that the inhibition of apoptosis may be mediated by a sequential pathway, including MAPK, COX-2, PGE(2) and c-IAP2, in the early period of stimulation. The delay in the onset of epithelial cell apoptosis after enterotoxigenic B. fragilis infection may be important to the host since it can provides sufficient time for epithelial cells to generate signals for the activation of mucosal inflammation and it may increase the chances of bacterial colonization.

Bacteroides fragilis toxin stimulates intestinal epithelial cell shedding and gamma-secretase-dependent E-cadherin cleavage

Enterotoxigenic Bacteroides fragilis - organisms that live in the colon - secrete a metalloprotease toxin, B. fragilis toxin. This toxin binds to a specific intestinal epithelial cell receptor and stimulates cell proliferation, which is dependent, in part, on E-cadherin degradation and beta-catenin-T-cell-factor nuclear signaling. Gamma-secretase (or presenilin-1) is an intramembrane cleaving protease and is a positive regulator of E-cadherin cleavage and a negative regulator of beta-catenin signaling. Here we examine the mechanistic details of toxin-initiated E-cadherin cleavage. B. fragilis toxin stimulated shedding of cell membrane proteins, including the 80 kDa E-cadherin ectodomain. Shedding of this domain required biologically active toxin and was not mediated by MMP-7, ADAM10 or ADAM17. Inhibition of gamma-secretase blocked toxin-induced proteolysis of the 33 kDa intracellular E-cadherin domain causing cell membrane retention of a distinct beta-catenin pool without diminishing toxin-induced cell proliferation. Unexpectedly, gamma-secretase positively regulated basal cell proliferation dependent on the beta-catenin-T-cell-factor complex. We conclude that toxin induces step-wise cleavage of E-cadherin, which is dependent on toxin metalloprotease and gamma-secretase. Our results suggest that differentially regulated beta-catenin pools associate with the E-cadherin-gamma-secretase adherens junction complex; one pool regulated by gamma-secretase is important to intestinal epithelial cell homeostasis.

Bacteroides fragilis enterotoxin induces cyclooxygenase-2 and fluid secretion in intestinal epithelial cells through NF-kappaB activation

Bacteroides fragilis produces an approximately 20-kDa heat-labile toxin (B. fragilis enterotoxin, BFT) which is known to be associated with diarrhea. To determine whether cyclooxygenase (COX)-2, via NF-kappaB activation, can contribute to BFT-induced diarrhea, the relationship between COX-2 expression and fluid secretion in BFT-stimulated human intestinal epithelial cells was examined. BFT stimulation increased the expression of COX-2, but not COX-1, in human intestinal epithelial cells. Suppression of the NF-kappaB signal significantly decreased COX-2 expression in response to BFT stimulation. Prostaglandin E2 (PGE2) levels were increased in parallel with COX-2 expression, and, conversely, PGE2 production was significantly inhibited when COX-2 or NF-kappaB activities were suppressed using COX-2 small interfering RNA (siRNA), p65 NF-kappaB subunit siRNA, or a retrovirus encoding the IkappaBalpha superrepressor. In addition, a selective COX-2 inhibitor, NS-398, significantly inhibited the increased cAMP level induced by BFT stimulation. Furthermore, a selective COX-2 inhibitor prevented BFT-induced PGE2 production and ileal fluid secretion in a mouse ileal loop model. These results suggest that the secretory response to BFT stimulation may be mediated by the production of PGE2, through NF-kappaB activation and the up-regulation of COX-2 in intestinal epithelial cells.

Evaluation of the pathogenicity of the Bacteroides fragilis toxin gene subtypes in gnotobiotic mice

Enterotoxigenic Bacteroides fragilis (ETBF) strains produce a metalloprotease toxin (BFT) related to diarrheal disease in animals, young children, and adults. Three different isoforms of the enterotoxin, designated BFT-1, BFT-2, and BFT-3, have been identified and sequenced. In the present study, the pathogenicity of the ETBF strains carrying bft-1 or bft-2 was evaluated. Each toxin gene subtype of ETBF (bft-1 or bft-2) was intragastrically monoassociated to germ-free mice during 10 days and histopathological data from intestines and liver compared with those from mice monoassociated to a non-enterotoxigenic B. fragilis. Histopathological alterations were observed in all groups of animals related to ETBF. These alterations were characterized mainly by ulceration, edema, and inflammatory infiltration in intestine. However, these lesions were slightly more severe in mice monoassociated with bft-2 subtype. No alteration or lesion was observed in animals associated with the non-enterotoxigenic B. fragilis. In conclusion, strains harboring bft-1 or bft-2 gene subtypes were able to induce histopathological alterations in intestine of a gnotobiotic mice model and it could explain the effect produced for the enterotoxin.

Enterotoxigenicity of mature 45-kilodalton and processed 35-kilodalton forms of hemagglutinin protease purified from a cholera toxin gene-negative Vibrio cholerae non-O1, non-O139 strain

Cholera toxin gene-negative Vibrio cholerae non-O1, non-O139 strain PL-21 is the etiologic agent of cholera-like syndrome. Hemagglutinin protease (HAP) is one of the major secretory proteins of PL-21. The mature 45-kDa and processed 35-kDa forms of HAP were purified in the presence and absence of EDTA from culture supernatants of PL-21. Enterotoxigenicities of both forms of HAP were tested in rabbit ileal loop (RIL), Ussing chamber, and tissue culture assays. The 35-kDa HAP showed hemorrhagic fluid response in a dose-dependent manner in the RIL assay. Histopathological examination of 20 microg of purified protease-treated rabbit ileum showed the presence of erythrocytes and neutrophils in the upper part of the villous lamina propria. Treatment with 40 microg of protease resulted in gross damage of the villous epithelium with inflammation, hemorrhage, and necrosis. The 35-kDa form of HAP, when added to the lumenal surface of rat ileum loaded in an Ussing chamber, showed a decrease in the intestinal short-circuit current and a cell rounding effect on HeLa cells. The mature 45-kDa form of HAP showed an increase in intestinal short-circuit current in an Ussing chamber and a cell distending effect on HeLa cells. These results show that HAP may play a role in the pathogenesis of PL-21.

Comparison of fecal microflora in children with atopic eczema/dermatitis syndrome according to IgE sensitization to food

Atopic eczema/dermatitis syndrome (AEDS) commonly often arises during early infancy. In several intervention studies a beneficial influence on AEDS course of certain intestinal bacteria, administered as 'probiotics', has been described. To evaluate the possible role of the natural intestinal microflora in children with allergic eczema/dermatitis syndrome regarding immediate type hypersensitivity to food allergens, children with food allergy (AAEDS, n = 68) have been compared with children without detectable food allergy (NAEDS, n = 25). All children (n = 93) in preschool age, mean age of 2.6 (+/-1.8) years, diagnosed with AEDS who were treated as inpatients in 2003 in a dermatological hospital were included. The correlation between fecal microflora, parasites and specific immunoglobulin E (IgE) antibodies against common food allergens was analyzed. A similar composition of intestinal microflora in children with AAEDS and NAAEDS was found. The food allergens that were most frequently detected were egg white, cow milk, casein, peanut and hazelnut. Furthermore, a significant association between IgE sensitization against important food allergens and components of the fecal microflora could not be demonstrated. With aging changes occur in the intestinal microbiota [Proteus/Klebsiella and age (rho = -0.607) and Enterococcus and age (rho = -0.428)]. In two subjects of the AAEDS group Blastocystis hominis was found. The composition of natural intestinal microflora in children with AAEDS and NAAEDS was similar. Hence, there is no evidence of a role of the intestinal microflora with regard to the development of infant (food) allergy in children with AEDS. The possible consequences for allergic diseases later in life require further investigation.

Mitogen-activated protein kinase and activator protein-1 dependent signals are essential for Bacteroides fragilis enterotoxin-induced enteritis

The approximately 20-kDa heat-labile toxin produced by enterotoxigenic Bacteroides fragilis is known to be associated with the development of enteritis. However, the molecular mechanism involved is not yet fully understood. In this study, we assessed whether B. fragilis enterotoxin (BFT)-induced enteritis is related to mitogen-activated protein kinase (MAPK) signaling pathways. In human colon epithelial cells, BFT activated three major MAPK cascades. The activation of p38 was sustained for a relatively long period, while the stimulation of extracellular signal-regulated kinases (ERK) and c-Jun N-terminal kinase (JNK) was transient. BFT stimulation also activated AP-1 signals composed of c-Jun/c-Fos heterodimers. The p38 inhibitor SB203580 and the ERK inhibitor U0126 reduced not only AP-1 activity, but also decreased IL-8 and MCP-1 expression. In addition, the overexpression of superrepressors for c-Jun and Ras induced by BFT stimulation decreased the levels of IL-8 and MCP-1 production. Furthermore, SB203580 prevented BFT-induced colitis in the mouse ileum, as evidenced by significant decreases in villous destruction, neutrophil infiltration, and mucosal congestion. These results suggest that a pathway, including Ras, MAPK, and subsequent AP-1 activation, is required for IL-8 and MCP-1 expression in intestinal epithelial cells exposed to BFT, and can be involved in the development of enteritis.

Induction of colonic transmural inflammation by Bacteroides fragilis: implication of matrix metalloproteinases

BACKGROUND

Commensal bacteria are implicated in the pathophysiology of intestinal inflammation, but the precise pathogenetic mechanisms are not known. We hypothesized that Bacteroides fragilis-produced metalloproteinases (MMPs) are responsible for bacterial migration through the intestinal wall and transmural inflammation.

AIM

To investigate the role of bacterial-MMP activity in an experimental model of colitis induced by the intramural injection of bacteria.

METHODS

Suspensions of viable B. fragilis or Escherichia coli were injected into the colonic wall, and the effect of the MMP inhibitor (phenantroline) on histologic lesion scores was tested. MMP activity in bacterial suspensions was measured by azocoll assay.

RESULTS

The inoculation with B. fragilis induced chronic inflammatory lesions that were preferentially located in the subserosa, whereas inoculation with E. coli induced acute-type inflammatory reactions, evenly distributed in both the submucosa and subserosa. Treatment with phenantroline significantly decreased subserosal lesion scores in rats inoculated with B. fragilis, but not in rats inoculated with E. coli. Bacterial suspensions of B. fragilis showed MMP activity, but E. coli suspensions did not. Sonication of B. fragilis reduced MMP activity and virulence to induce serosal lesions.

CONCLUSION

Our data suggest that bacterial MMPs may be implicated in the serosal migration of B. fragilis and in the induction of transmural inflammation.

Bacteroides fragilis enterotoxin induces intestinal epithelial cell secretion of interleukin-8 through mitogen-activated protein kinases and a tyrosine kinase-regulated nuclear factor-kappaB pathway

Enterotoxigenic Bacteroides fragilis (ETBF) secretes a 20-kDa metalloprotease toxin termed B. fragilis toxin (BFT). ETBF disease in animals is associated with an acute inflammatory response in the intestinal mucosa, and lethal hemorrhagic colitis may occur in rabbits. In this study, we confirmed recent reports (J. M. Kim, Y. K. Oh, Y. J. Kim, H. B. Oh, and Y. J. Cho, Clin. Exp. Immunol. 123:421-427, 2001; L. Sanfilippo, C. K. Li, R. Seth, T. J. Balwin, M. J. Menozzi, and Y. R. Mahida, Clin. Exp. Immunol. 119:456-463, 2000) that purified BFT stimulates interleukin-8 (IL-8) secretion by human intestinal epithelial cells (HT29/C1 cells) and demonstrate that stimulation of IL-8 production is dependent on biologically active BFT and independent of serum. Induction of IL-8 mRNA expression occurs rapidly and ceases by 6 h after BFT treatment, whereas IL-8 secretion continues to increase for at least 18 h. Our data suggest that BFT-stimulated IL-8 secretion involves tyrosine kinase-dependent activation of nuclear factor-kappaB (NF-kappaB) as well as activation of the mitogen-activated protein kinases (MAPKs), p38 and extracellular signal-related kinase. Simultaneous activation of NF-kappaB and MAPKs appears necessary for secretion of IL-8 by HT29/C1 cells treated with BFT.

Microbial-gut interactions in health and disease. Epithelial cell responses

Intestinal epithelial cells are unique in that they represent the only host cells that are constantly interacting with a very large bacterial population in the lumen. The single monolayer of epithelial cells consists of subpopulations with distinct functions that include protection against luminal microorganisms. Although the microbial flora remains to be fully characterized, its normal relationship with the host intestinal epithelial cells appears to be predominantly symbiotic or commensal. The molecular complexity of the epithelial-microbial relationship has been shown in studies that have examined the establishment of the resident bacteria in germ-free mice. Recent work has also demonstrated the ability of resident bacteria to enhance epithelial protective responses. The mechanisms by which epithelial cells may avoid pro-inflammatory responses to resident microorganisms, while retaining the capacity to respond to pathogens, are also being characterized.

Detection of non-enterotoxigenic and enterotoxigenic Bacteroides fragilis in stool samples from children in São Paulo, Brazil

Non-enterotoxigenic bacteria of the Bacteroides fragilis group and enterotoxigenic B. fragilis were identified from children with and without aqueous acute diarrhea. In this study, 170 stool samples from 96 children with and 74 without diarrhea were analyzed. Enterotoxin production and the toxin gene detection were detected by cytotoxicity assay on HT-29/C1 cells and by PCR, respectively. B. fragilis species was prevalent in both groups and enterotoxigenic B. fragilis strains were isolated from two children with diarrhea. More studies are important to evaluate the role of each bacteria of the B. fragilis group, including enterotoxigenic strains play in the diarrheal processes in children.

Nuclear factor-kappa B activation pathway in intestinal epithelial cells is a major regulator of chemokine gene expression and neutrophil migration induced by Bacteroides fragilis enterotoxin

Although intestinal epithelial cells are known to up-regulate the expression of several chemokine genes in response to the stimulation with B. fragilis enterotoxin (BFT), there has been little understanding on the cellular mechanisms of BFT-induced mucosal inflammation. To test whether nuclear transcriptional factor-kappa B (NF-kappaB) is involved in the process, we stimulated intestinal epithelial cells with BFT, and evaluated the signalling NF-kappaB pathways. BFT increased signals of NF-kappaB in HT-29 and T84 epithelial cell lines as well as primary human colon epithelial cells. NF-kappaB molecules activated by BFT stimulation were composed of p65 and p50 heterodimers. In contrast, BFT decreased the signals of IkappaBalpha and IkappaB epsilon, as assessed by immunoblot. Super-repressors of IkappaBalpha, IkappaB kinase (IKK)beta, and NF-kappaB inducing kinase (NIK) inhibited an up-regulated transcription of downstream target gene (CXCL8) of NF-kappaB. Moreover, blocking the activation of NF-kappaB by MG-132 or antisense p50 oligonucleotide transfection resulted in down-regulated expression of chemokines such as CXCL1, CXCL8, and CCL2 in BFT-stimulated HT-29 cells. In addition, NF-kappaB inhibition suppressed the BFT-induced neutrophil transepithelial migration in T84 cells. These results indicate that NF-kappaB can be a central regulator of chemokine gene expression in BFT-stimulated intestinal epithelial cells and may be an important regulator of neutrophil migration.

MMPs and TIMPs--an historical perspective

There are currently 25 known vertebrate matrix metalloproteinases (MMPs) and 4 tissue inhibitors of metalloproteinases (TIMPs). This article reviews these proteases from an historical perspective in terms of who discovered each protein, when the sequence was established, when action on protein substrates was demonstrated, and what names have been used. A similar approach is taken for the TIMPS, and their multiple functions in addition to protease inhibition are emphasized. MMPs from invertebrates, plants, and bacteria are also discussed. This review is an outgrowth and update of a chapter by the same name originally published in Matrix Metalloproteinase Protocols, pp. 1-23, edited by I. M. Clark and published by Humana Press in 2001.

Aberrant composition of gut microbiota of allergic infants: a target of bifidobacterial therapy at weaning?

BACKGROUND

Recent data have outlined a relationship between the composition of the intestinal microflora and allergic inflammation, and demonstrated the competence of probiotics in downregulation of such inflammation.

AIMS

Our aims were to characterise the relationship between gut microbes and the extent of allergic sensitisation and to assess whether the efficacy of bifidobacterial supplementation in the treatment of allergy could relate to modulation of the intestinal microbiota.

METHODS

This randomised study included 21 infants with early onset atopic eczema of whom eight were intolerant (highly sensitised group (HSG)) and 13 tolerant (sensitised group (SG)) to extensively hydrolysed whey formula (EHF). In the SG, six were weaned to EHF without (placebo group (PG)) and seven to EHF with Bifidobacterium lactis Bb-12 supplementation (bifidobacteria treated group (BbG)). The faecal microflora of infants in the HSG was analysed only before weaning whereas in the SG the faecal microflora was analysed both before and after weaning.

RESULTS

Infants in the HSG had greater numbers of lactobacilli/enterococci than those in the SG. Serum total IgE concentration correlated directly with Escherichia coli counts in all infants and with bacteroides counts in the HSG, indicating that the presence of these bacteria is associated with the extent of atopic sensitisation. The effect of supplementation was characterised as a decrease in the numbers of Escherichia coli and protection against an increase in bacteroides numbers during weaning.

CONCLUSIONS

These data indicate that bifidobacterial supplementation appears to modify the gut microbiota in a manner that may alleviate allergic inflammation. Further studies are needed to confirm this conclusion.

Diversity of the metalloprotease toxin produced by enterotoxigenic Bacteroides fragilis

Enterotoxigenic Bacteroides fragilis (ETBF) strains produce a 20-kDa zinc metalloprotease toxin (BFT) associated with diarrheal disease of animals, young children, and adults. BFT stimulates secretion in intestinal loops in vivo and modifies epithelial cell morphology in vitro. The B. fragilis toxin (bft) gene from ETBF strain 86-5443-2-2 (piglet; bft-2) revealed significant nucleotide and predicted amino acid differences when compared to the bft gene from ETBF strain VPI 13784 (lamb; bft-1). This study compares BFT-1 and BFT-2, respectively, produced by ETBF strains VPI 13784 and 86-5443-2-2 purified using the Van Tassell method (38) and a modified purification scheme described herein. Multiple differences in the protein toxins produced by these ETBF strains were identified. First, purified BFT-1 eluted from a high-resolution anion-exchange column (Mono Q) at 0.22 +/- 0.005 M NaC1 versus 0.18 +/- 0.001 M NaC1 for BFT-2 (P < 0.001). Second, BFT-1 and BFT-2 exhibited different electrophoretic mobilities on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reverse-phase fast protein liquid chromatography. Third, each BFT reacted with greater specificity to homologous rather than heterologous antisera. Fourth, BFT-2 had modest, but consistently, greater biological activity than BFT-1 when tested on HT29/C1 cells (P < or = 0.01). Together, these data indicate that these ETBF strains produce two distinct isotypes of BFT, termed BFT-1 (VPI 13784 BFT) and BFT-2 (86-5443-2-2 BFT) to recognize the order in which the proteins were purified and genetic sequences identified. The modified purification scheme described in this report yields about two to three times more purified BFT protein than previous protocols and is less time consuming.

Bacteroides ovatus as the predominant commensal intestinal microbe causing a systemic antibody response in inflammatory bowel disease

To clarify what bacterial species of commensal intestinal microbes are recognized as the antigens that induce a serum antibody response in patients with inflammatory bowel disease (IBD), 72 subjects consisting of 12 Crohn's disease patients, 30 ulcerative colitis patients, and 30 healthy volunteers were examined for their titers of serum antibody to these intestinal bacteria. In IBD patients, as a result, significant elevations of both the immunoglobulin G (IgG) and IgA titers to Bacteroides ovatus were found. Immunoblotting showed that a definite 19.5-kDa band of B. ovatus was bound to the serum antibody raised in IBD patients. It was thus concluded that B. ovatus causes serum antibody responses in IBD patients, and a 19.5-kDa molecule of this bacterium appears to be the responsible antigen, although the role of this event in pathogenesis remains unclear.

The toxins of Bacteroides fragilis

Bacteroides fragilis are both key commensals and important human pathogens. Particular strains of B. fragilis, termed enterotoxigenic B. fragilis (ETBF), are recently identified enteric pathogens of children and adults. These strains are distinguished by secretion of a 20kDa metalloprotease toxin (B. fragilis toxin or BFT), the first recognized and only established toxin to date for B. fragilis. Three isotypes of BFT are encoded by distinct bft loci contained within a 6kb chromosomal region unique to ETBF strains termed the B. fragilis pathogenicity island (BfPAI). Experimental studies have suggested that the cellular target for BFT is E-cadherin, the primary protein of the zonula adherens. It is postulated that BFT cleavage of E-cadherin is critical in precipitating the intracellular events culminating in the two established activities for BFT; namely, stimulation of secretion in ligated intestinal segments in several animal species and alteration of cellular morphology only in epithelial cells that retain the ability to polarize and form a tight junctional complex. Future studies will be directed to characterizing in greater detail both the molecular genetics of the BFT toxin and the precise steps in its cellular mechanism of action.

The cell envelope-bound metalloprotease (camelysin) from Bacillus cereus is a possible pathogenic factor

A novel membrane proteinase of the nosocomial important bacteria species Bacillus cereus (synonyms: camelysin, CCMP) was purified up to homogeneity as was shown by mass spectrometry in its amphiphilic form. Camelysin is a neutral metalloprotease with a molecular mass of 19 kDa. Its unique N-terminus Phe-Phe-Ser-Asp-Lys-Glu-Val-Ser-Asn-Asn-Thr-Phe-Ala-Ala-Gly-Thr-Leu-Asp-Leu-Thr-Leu-Asn-Pro-Lys-Thr-Leu-Val-Asp-(Ile-Lys-Asp)- was not detected in the protein data bases during BLAST searches, but in the partially sequenced genome of Bacillus anthracis, coding for an unknown protein. Cleavage sites of the membrane proteinase for the insulin A- and B-chains were determined by mass spectrometry and N-terminal sequencing. Camelysin prefers cleavage sites in front of aliphatic and hydrophilic amino acid residues (-OH, -SO3H, amido group), avoiding bulky aromatic residues. The internally quenched fluorogenic substrates of the matrix metalloproteases 2 and 7 were cleaved with the highest efficiency at the Leu-decrease-Gly or Leu-decrease-Ala bond with the smaller residue in the P1' position. The protein specificity is broad--all various kinds of casein were cleaved as well as acid-soluble collagen, globin and ovalbumin; intact insulin was destroyed only to a low extent. Actin, collagen type I, fibrinogen, fibrin, alpha2-antiplasmin and alpha1-antitrypsin were cleaved. The protease formed SDS-stable complexes with Glu-plasminogen and antithrombin III, visible after SDS electrophoresis by gold staining and Western blot. The CCMP-plasminogen complex caused a partial activation of plasminogen to plasmin. Camelysin interacts with proteins of the blood coagulation cascade and could facilitate the penetration of fibrin clots and of the extracellular matrix during bacterial invasion.

Polarized secretion of CXC chemokines by human intestinal epithelial cells in response to Bacteroides fragilis enterotoxin: NF-kappa B plays a major role in the regulation of IL-8 expression

Enterotoxigenic B. fragilis, which produces a approximately 20 kD heat-labile toxin (BFT), has been associated with diarrhoeal diseases and mucosal inflammation. To determine if epithelial cells can contribute to BFT-induced inflammation, we assessed the expression of CXC chemokines by BFT-stimulated human intestinal epithelial cells. BFT stimulation increased expression of the neutrophil chemoattractant and activators ENA-78, GRO-alpha, and IL-8. Up-regulated chemokine mRNA expression was paralleled by increased protein levels. Activation of the IL-8 and NF-kappa B transcriptional reporters was inhibited in cells cotransfected with the I kappa B kinase beta and IkB alpha superrepressor plasmids. Whereas lactate dehydrogenase, which was used to monitor cell lysis, was released predominantly from the apical surface, CXC chemokines were predominantly secreted from the basolateral surface of BFT-treated epithelial cells. The basolateral secretion of CXC chemokines from BFT-stimulated colon epithelial cells suggests that these chemokines can contribute to the inflammatory cell infiltrate in the underlying intestinal mucosa.

Production of a mouse antiserum to Bacteroides fragilis enterotoxin using a recombinant enterotoxin precursor

The precursor of the Bacteroides fragilis metalloprotease enterotoxin was cloned and expressed in Escherichia coli, which was not able to process the precursor into the biologically active enterotoxin. Mouse antiserum elicited to the recombinant precursor reacted with the purified enterotoxin and with a crude enterotoxin preparation from an enterotoxigenic strain. The antiserum neutralized the cytotoxic activity of the enterotoxin in HT-29 cells.

Fragilysin, the enterotoxin from Bacteroides fragilis, enhances the serum antibody response to antigen co-administered by the intranasal route

Fragilysin, an extracellular zinc metalloprotease produced by enterotoxigenic strains of the anaerobic bacterium Bacteroides fragilis, disrupts the paracellular barrier by cleavage of the intercellular proteins between epithelial cells resulting in fluid secretion. Intranasal immunization of mice with fragilysin and co-administered ovalbumin (Ova) resulted in an Ova-specific serum IgG response that was over 18000-fold higher than Ova alone, as well as detectable levels of serum IgA. Serum IgG titers were comparable with those seen when whole cholera toxin was used as the adjuvant, although the responses obtained with fragilysin showed more variability between mice. Metalloproteases to which fragilysin is structurally related were ineffective as mucosal adjuvants. Our results and similar studies with enterotoxins that affect the paracellular barrier suggest that alteration of mucosal permeability may play an important role in the mechanisms of adjuvanticity.

Bacteroides fragilis toxin rearranges the actin cytoskeleton of HT29/C1 cells without direct proteolysis of actin or decrease in F-actin content

Enterotoxigenic strains of B. fragilis associated with childhood diarrhea produce a 20 kD zinc metalloprotease toxin (BFT). BFT is reported to cleave G-actin in vitro and also causes dramatic rounding and rearrangement of the F-actin cytoskeleton in human intestinal epithelial cell lines (HT29) and HT29/C1). To test the hypothesis that the proteolysis of cellular actin by BFT in vivo may contribute to these alterations in morphology and cytoskeletal architecture, we assessed the F-actin content and the arrangement of the F- and G-actin cytoskeleton in BFT-treated HT29/C1 cells by spectrofluorimetry, confocal microscopy, and immunoblotting. BFT-treated cells were compared to cells treated with C. difficile toxin A (CDA) or cytochalasin D. Using spectrofluorimetric quantification, the F-actin content of BFT- and cytochalasin D-treated cells was unchanged in contrast to a significant decrease in CDA-treated cells. By confocal microscopy, the arrangement of F- and G-actin in all treated cells was markedly different than control cells. There was no change in the immunoblotting pattern of actin in the Triton-soluble or -insoluble cellular fractions of BFT-treated HT29/C1 cells. We conclude that BFT alters the F- and G-actin cytoskeletal architecture of HT29/C1 cells without direct proteolysis of actin or decrease in F-actin content.