Environment as a Critical Factor for the Pathogenesis and Outcome of Gastrointestinal Disease: Experimental and Human Inflammatory Bowel Disease and Helicobacter-Induced Gastritis

What we need to know about the germ-free animal models

The gut microbiota (GM), as a forgotten organ, refers to the microbial community that resides in the gastrointestinal tract and plays a critical role in a variety of physiological activities in different body organs. The GM affects its targets through neurological, metabolic, immune, and endocrine pathways. The GM is a dynamic system for which exogenous and endogenous factors have negative or positive effects on its density and composition. Since the mid-twentieth century, laboratory animals are known as the major tools for preclinical research; however, each model has its own limitations. So far, two main models have been used to explore the effects of the GM under normal and abnormal conditions: the isolated germ-free and antibiotic-treated models. Both methods have strengths and weaknesses. In many fields of host-microbe interactions, research on these animal models are known as appropriate experimental subjects that enable investigators to directly assess the role of the microbiota on all features of physiology. These animal models present biological model systems to either study outcomes of the absence of microbes, or to verify the effects of colonization with specific and known microbial species. This paper reviews these current approaches and gives advantages and disadvantages of both models.

Interfering With Inflammation: Heterogeneous Effects of Interferons in Graft-Versus-Host Disease of the Gastrointestinal Tract and Inflammatory Bowel Disease

The intestine can be the target of several immunologically mediated diseases, including graft-versus-host disease (GVHD) and inflammatory bowel disease (IBD). GVHD is a life-threatening complication that occurs after allogeneic hematopoietic stem cell transplantation. Involvement of the gastrointestinal tract is associated with a particularly high mortality. GVHD development starts with the recognition of allo-antigens in the recipient by the donor immune system, which elicits immune-mediated damage of otherwise healthy tissues. IBD describes a group of immunologically mediated chronic inflammatory diseases of the intestine. Several aspects, including genetic predisposition and immune dysregulation, are responsible for the development of IBD, with Crohn’s disease and ulcerative colitis being the two most common variants. GVHD and IBD share multiple key features of their onset and development, including intestinal tissue damage and loss of intestinal barrier function. A further common feature in the pathophysiology of both diseases is the involvement of cytokines such as type I and II interferons (IFNs), amongst others. IFNs are a family of protein mediators produced as a part of the inflammatory response, typically to pathogens or malignant cells. Diverse, and partially paradoxical, effects have been described for IFNs in GVHD and IBD. This review summarizes current knowledge on the role of type I, II and III IFNs, including basic concepts and controversies about their functions in the context of GVHD and IBD. In addition, therapeutic options, research developments and remaining open questions are addressed.

Helicobacter pylori promote inflammation and host defense through the cagA-dependent activation of mTORC1

Mechanistic target of rapamycin complex 1 (mTORC1) functions as regulating different cellular processes, including cell growth, proliferation, motility, survival, metabolism, autophagy, and protein transcription. Recently, it also found to be associated with many infections and inflammatory diseases, playing complex roles in pathogens growth and inflammation regulation. However, the regulation mechanism of mTORC1 in gastric epithelial cells and its role in Helicobacter pylori (H. pylori) infection and related gastritis remain unclear. Here, we identified that the phosphorylation of mechanistic target of rapamycin (mTOR) and the expression of DEP domain-containing mTOR-interacting protein (DEPTOR) was increased in gastric mucosa of H. pylori-infected patients and mice, as well as in H. pylori-infected gastric epithelial cells, which were largely depended on H. pylori cagA. The expression of DEPTOR was regulated via mTORC1, but, in turn, inhibited mTORC1. Knockdown mTOR significantly decreased expression and secretion of cytokines tumor necrosis factor-α, interleukin-1β, and interleukin-6, chemokines CCL7 and CXCL16, and antimicrobial peptide LL37 in vitro, while knockdown DEPTOR had the opposite effect. Similar observations were made using mTOR knockout (KO) mice in vivo, moreover. The gastric inflammation was attenuated, while the bacterial burden was increased in mTOR KO mice during H. pylori infection. These findings supported H. pylori promote gastritis and inhibit bacterial colonization through the cagA-dependent activation of mTORC1.

Analysis of Cdcs1 colitogenic effects in the hematopoietic compartment reveals distinct microbiome interaction and a new subcongenic interval active in T cells

Disease activity in Interleukin-10-deficient (Il10^-/-) mice, a model for IBD, depends on genetic background and microbiome composition. B6.129P2/JZtm-Il10^tm1Cgn (B6-Il10^-/-) mice are partially resistant to colitis, whereas mice carrying the Cdcs1^C3Bir haplotype on chromosome 3, B6.Cg-Il10^tm1CgnMMU3(D3Mit11-D3Mit348)/JZtm (BC-R3-Il10^-/-), are susceptible. This study was performed to clarify Cdcs1 and candidate gene effects on the colitogenic potential of hematopoietic cells using bone marrow (BM) and T-cell transfer models. Acute and chronic graft versus host reaction was excluded by high-density genotyping, in vitro and in vivo approaches. BM-chimeras were created with animals housed in two barriers (I and II) with distinct microbiota composition as identified by sequencing. BM-chimeras of all groups developed comparable moderate-to-severe colitis in Barrier I, however, in Barrier II only recipients of BC-R3-Il10^-/- BM. Subsequent adoptive T cell transfers pointed to a new subcongenic interval within Cdcs1 affecting their colitogenic potential. Transfers excluded Larp7 and Alpk1 but highlighted Ifi44 as potential candidate genes. In this model-system, colitis development after cell transfer heavily depends on microbiome, though Cdcs1 acts mainly independently in hematopoietic cells. A new subcongenic interval, provisionally named Cdcs1.4, modifies colitogenic T cell function. Within this locus, Ifi44 represents an important candidate gene for colitis expression.

The Protective Role of Type I Interferons in the Gastrointestinal Tract

The immune system of the gastrointestinal (GI) tract manages the significant task of recognizing and eliminating pathogens while maintaining tolerance of commensal bacteria. Dysregulation of this delicate balance can be detrimental, resulting in severe inflammation, intestinal injury, and cancer. Therefore, mechanisms to relay important signals regulating cell growth and immune reactivity must be in place to support GI homeostasis. Type I interferons (IFN-I) are a family of pleiotropic cytokines, which exert a wide range of biological effects including promotion of both pro- and anti-inflammatory activities. Using animal models of colitis, investigations into the regulation of intestinal epithelium inflammation highlight the role of IFN-I signaling during fine modulation of the immune system. The intestinal epithelium of the gut guides the immune system to differentiate between commensal and pathogenic microbiota, which relies on intimate links with the IFN-I signal-transduction pathway. The current paradigm depicts an IFN-I-induced antiproliferative state in the intestinal epithelium enabling cell differentiation, cell maturation, and proper intestinal barrier function, strongly supporting its role in maintaining baseline immune activity and clearance of damaged epithelia or pathogens. In this review, we will highlight the importance of IFN-I in intestinal homeostasis by discussing its function in inflammation, immunity, and cancer.

A Review of Applied Aspects of Dealing with Gut Microbiota Impact on Rodent Models

The gut microbiota (GM) affects numerous human diseases, as well as rodent models for these. We will review this impact and summarize ways to handle this challenge in animal research. The GM is complex, with the largest fractions being the gram-positive phylum Firmicutes and the gram-negative phylum Bacteroidetes. Other important phyla are the gram-negative phyla Proteobacteria and Verrucomicrobia, and the gram-positive phylum Actinobacteria. GM members influence models for diseases, such as inflammatory bowel diseases, allergies, autoimmunity, cancer, and neuropsychiatric diseases. GM characterization of all individual animals and incorporation of their GM composition in data evaluation may therefore be considered in future protocols. Germfree isolator-housed rodents or rodents made virtually germ free by antibiotic cocktails can be used to study diverse microbial influences on disease expression. Through subsequent inoculation with selected strains or cocktails of microbes, new "defined flora" models can yield valuable knowledge on the impact of the GM, and of specific GM members and their interactions, on important disease phenotypes and mechanisms. Rodent husbandry and microbial quality assurance practices will be important to ensure and confirm appropriate and research relevant GM.

The Mammalian Microbiome and Its Importance in Laboratory Animal Research

In this issue are assembled 10 fascinating, well-researched papers that describe the emerging field centered on the microbiome of vertebrate animals and how these complex microbial populations play a fundamental role in shaping homeostasis of the host. The content of the papers will deal with bacteria and, because of relative paucity of information on these organisms, will not include discussions on viruses, fungus, protozoa, and parasites that colonize various animals. Dissecting the number and interactions of the 500-1000 bacterial species that can inhabit the intestines of animals is made possible by advanced DNA sequencing methods, which do not depend on whether the organism can be cultured or not. Laboratory animals, particularly rodents, have proven to be an indispensable component in not only understanding how the microbiome aids in digestion and protects the host against pathogens, but also in understanding the relationship of various species of bacteria to development of the immune system. Importantly, this research elucidates purported mechanisms for how the microbiome can profoundly affect initiation and progression of diseases such as type 1 diabetes, metabolic syndromes, obesity, autoimmune arthritis, inflammatory bowel disease, and irritable bowel syndrome. The strengths and limitations of the use of germfree mice colonized with single species of bacteria, a restricted flora, or most recently the use of human-derived microbiota are also discussed.

Antibiotic-treated versus germ-free rodents for microbiota transplantation studies

We recently investigated the applicability of antibiotic-treated recipient mice for transfer of different gut microbiota profiles. With this addendum we elaborate on perspectives and limitations of using antibiotics as an alternative to germ-free (GF) technology in microbial transplantation studies, and we speculate on the housing effect. It is possible to transfer host phenotypes via fecal transplantation to antibiotic-treated animals, but problems with reproducibility, baseline values, and antibiotic resistance genes should be considered. GF animals maintained in isolators still seem to be the best controlled models for long-term microbial transplantation, but antibiotic-treated recipients are also commonly utilized. We identify a need for systematic experiments investigating the stability of microbial transplantations by addressing 1) the recipient status as either GF, antibiotic-treated or specific pathogen free and 2) different levels of protected housing systems. In addition, the developmental effect of microbes on host physiological functions should be evaluated in the different scenarios.

A Multihit Model: Colitis Lessons from the Interleukin-10-deficient Mouse

Complex mechanisms are pulling the strings to initiate the development of inflammatory bowel disease. Current evidence indicates that an interaction of genetic susceptibilities (polymorphisms), environmental factors, and the host microbiota leads to a dysregulation of the mucosal immune system. In the past decades, the interleukin-10-deficient mouse has served as an excellent model to mirror the multifactorial nature of this disease. Here, we want to review in detail the interplay of the genetic factors, immune aspects, and especially summarize and discuss the role of the microbiota contributing to colitis development in the interleukin-10-deficient mouse model of inflammatory bowel disease as a multihit model.

Mapping colitis susceptibility in mouse models: distal chromosome 3 contains major loci related to Cdcs1

Inflammatory bowel disease (IBD) summarizes a group of chronic intestinal disorders with Crohn's disease and ulcerative colitis being most prominent. Though much effort is put into identification of causative factors, its etiology is still not understood. Risk factors for disease development include genetic predisposition and environmental triggers. Crucial for identification and analysis of relevant factors are mouse models. Experimental IBD in mice occurs spontaneously or is induced by chemicals, cell transfer, pathogens, or genetic mutation. These models were utilized for analyzing genetic contribution to disease and genotype-environmental interactions. In these studies, a variety of modifier loci were identified, thereby demonstrating the complexity of disease. A major contribution of distal chromosome 3 was independently replicated in several studies. The first colitogenic QTL in this region was detected using the IL-10-deficient mouse model and called cytokine deficiency-induced colitis susceptibility (Cdcs)1. This quantitative trait locus contains at least three subintervals with independent genetic factors. This locus or defined subintervals were replicated in at least seven studies, using models based on dysregulation of innate or adaptive immunity or pathogen control. In this review we illustrate the various models used for genetic mapping of susceptibility to experimental IBD and display Cdcs1-related loci as well as the mechanism of their contribution identified so far.

Strain-specific colitis susceptibility in IL10-deficient mice depends on complex gut microbiota-host interactions

BACKGROUND

Colitis susceptibility in Il10(-/-) mice depends on genetic background and microbiota composition. A major genetic locus mediating colitis susceptibility, Cdcs1, was transferred from susceptible C3Bir-Il10(-/-) to resistant B6-Il10(-/-) mice, resulting in susceptible congenic BC-R3-Il10(-/-) mice. The aim of this study was to determine the impact of microbiota on this differential colitis susceptibility using a Helicobacter hepaticus infection model.

METHODS

Parental C3Bir-Il10(-/-) , B6-Il10(-/-) , and congenic BC-R3-Il10(-/-) mice were inoculated with H. hepaticus and analyzed for inflammation. In parental Il10(-/-) mice, microbiota composition was determined by terminal restriction fragment length polymorphism (T-RFLP) and quantitative polymerase chain reaction (qPCR).

RESULTS

Most severe inflammation was observed in C3Bir-Il10(-/-) in the cecum, in BC-R3-Il10(-/-) in cecum and colon, and, unexpectedly, in B6-Il10(-/-) in the colon. C3Bir-Il10(-/-) and BC-R3-Il10(-/-) secreted significantly more interferon-gamma (IFNγ) and interleukin (IL)17 than B6-Il10(-/-) . T-RFLP analyses in C3Bir-Il10(-/-) and B6-Il10(-/-) mice revealed 1) a significant impact of H. hepaticus infection on species richness and diversity, and 2) strain differences in microbiota composition only after H. hepaticus infection. qPCR revealed higher numbers of Clostridia leptum and Bacteroides spp. in the cecum of infected C3Bir-Il10(-/-) mice, and Lactobacillus spp. in B6-Il10(-/-) mice.

CONCLUSIONS

Cdcs1 modifies the response to H. hepaticus infection. However, this infection alone does not reflect the original response to a complex colitogenic biota. H. hepaticus-induced inflammation altered intestinal microbiota in a mouse strain-specific manner. Bacteroides spp. became more abundant in susceptible C3Bir-Il10(-/-) , lactobacilli in B6-Il10(-/-) mice. Therefore, both host immune response and differential compositional changes of microbiota play a role in strain-specific colitis susceptibility in Il10(-/-) mice.

Time to include the gut microbiota in the hygienic standardisation of laboratory rodents

The gut microbiota (GM) composition and its impact on animal experiments has become currently dramatically relevant in our days: (1) recent progress in metagenomic technologies, (2) the availability of large scale quantitative analyses to characterize even subtle phenotypes, (3) the limited diversity of laboratory rodent GM due to strict barriers at laboratory animal vendors, and (4) the availability of up to 300.000 different transgenic mouse strains from different sources displaying a huge variety in their GM composition. In this review the GM is described as a variable in animal experiments which need to be reduced for scientific as well as ethical reasons, and strategies how to implement this in routine diagnostic procedures are proposed. We conclude that we have both enough information available to state that the GM has an essential impact on animal models, as well as the methods available to start dealing with these impacts.

Complete killing of Caenorhabditis elegans by Burkholderia pseudomallei is dependent on prolonged direct association with the viable pathogen

Background

Burkholderia pseudomallei is the causative agent of melioidosis, a disease of significant morbidity and mortality in both human and animals in endemic areas. Much remains to be known about the contributions of genotypic variations within the bacteria and the host, and environmental factors that lead to the manifestation of the clinical symptoms of melioidosis.

Methodology/Principal Findings

In this study, we showed that different isolates of B. pseudomallei have divergent ability to kill the soil nematode Caenorhabditis elegans. The rate of nematode killing was also dependent on growth media: B. pseudomallei grown on peptone-glucose media killed C. elegans more rapidly than bacteria grown on the nematode growth media. Filter and bacteria cell-free culture filtrate assays demonstrated that the extent of killing observed is significantly less than that observed in the direct killing assay. Additionally, we showed that B. pseudomallei does not persistently accumulate within the C. elegans gut as brief exposure to B. pseudomallei is not sufficient for C. elegans infection.

Conclusions/Significance

A combination of genetic and environmental factors affects virulence. In addition, we have also demonstrated that a Burkholderia-specific mechanism mediating the pathogenic effect in C. elegans requires proliferating B. pseudomallei to continuously produce toxins to mediate complete killing.

Protease-activated receptor-1 down-regulates the murine inflammatory and humoral response to Helicobacter pylori

BACKGROUND & AIMS

Helicobacter pylori infection results in a diversity of pathologies, from asymptomatic gastritis to adenocarcinoma. The reason for these diverse outcomes is multifactorial and includes host factors that regulate severity of Helicobacter-induced gastritis. Protease-activated receptors (PAR) are environmental sensors that can detect tissue damage and pathogens. Whereas PAR-2 has proinflammatory activity and PAR-1 can protect the gastric mucosa against chemical damage, neither has previously been examined for their potential roles in regulating Helicobacter pathogenesis.

METHODS

PAR-1(-/-), PAR-2(-/-), and wild-type mice were infected with H pylori for up to 2 months then colonization levels determined by colony-forming assay, gastritis by histology, and serum antibody levels by enzyme-linked immunosorbent assay. Responsiveness of primary epithelial cells to PAR-1 activation was assessed by calcium mobilization assay. Primary epithelial cells, macrophages, and dendritic cells were cocultured with H pylori and nuclear factor (NF)-kappaB, and cytokine secretion was determined by enzyme-linked immunosorbent assay.

RESULTS

Two months postinfection, H pylori levels were significantly reduced in PAR-1(-/-) and increased in PAR-2(-/-) mice. This effect on colonization was inversely correlated with inflammation severity. Infection of PAR-1(-/-) mice induced an increased serum antibody response. Primary epithelial cells were activated by a PAR-1-activating peptide. H pylori stimulation of primary epithelial cells, but not macrophages or dendritic cells, from PAR-1(-/-) mice induced increased levels of NF-kappaB and the proinflammatory cytokine macrophage-inflammatory protein (MIP)-2. PAR-1 also down-regulated MIP-2 secretion in response to cag pathogenicity island activity.

CONCLUSIONS

PAR-1 protects the host against severe Helicobacter-induced gastritis. This may be mediated by suppressing the production of proinflammatory cytokines such as MIP-2.

Analysis of Cd14 as a genetic modifier of experimental inflammatory bowel disease (IBD) in mice

BACKGROUND AND AIM

By combining QTL and gene expression analyses, we have previously identified Cd14 as a potential candidate gene contributing to the differential IBD susceptibility of C3H/HeJBir (C3/J)-Il10(-/-) mice [carrying IBD-resistance alleles at this QTL (Cdcs6)] and C57BL/6J (B6)-Il10(-/-) mice, corroborating studies that showed an association of a CD14-promoter polymorphism with Crohn's disease and ulcerative colitis. The aim of the present study was to analyze the molecular mechanisms leading to differential intestinal expression of Cd14 and its contribution to IBD development.

METHODS

Intestinal CD14 expression was assessed by FACS, immunohistochemistry, and ELISA on supernatants of primary epithelial cell and tissue cultures. RAW264.7 cells were stimulated with LPS and PGN in the presence or absence of CD14. Cd14 alleles were sequenced and promoters cloned for luciferase assays in transfected RAW264.7 cells. The severity of typhlocolitis between Cd14(-/-) and wild-type mice was compared in 2 distinct mouse models of IBD (acute DSS and Il10(-/-) ).

RESULTS

In the gut, CD14 was detected mainly in its soluble form (sCD14), with higher expression in C3/J-Il10(-/-) mice. Polymorphisms in C3/J mice caused higher activity of the Cd14 promoter (luciferase assays). Intestinal sCD14 concentrations influenced the LPS and PGN responses of RAW264.7 cells. In vivo, genetic deletion of Cd14 aggravated colitis in both mouse models of IBD.

CONCLUSIONS

Our study shows that Cd14-promoter polymorphisms affect CD14 expression and confirms the protective effect of CD14 against experimental IBD, potentially mediated by TLR2- and TLR4-dependent effects on intestinal barrier function. These findings support the concept that human CD14-promoter polymorphisms contribute to disease development.

Helicobacter-based mouse models of digestive system carcinogenesis

Animal models are necessary to reproduce the complex host, microbial and environmental influences associated with infectious carcinogenesis of the digestive system. Today, mouse models are preferred by most researchers because of cost efficiencies, rapid reproduction, choice of laboratory reagents, and availability of genetically engineered mutants to study specific gene functions in vivo. Mouse models have validated the once-provocative hypothesis that Helicobacter pylori infection is a major risk factor for gastric carcinoma, dispelling early skepticism over the pathogenic nature of this organism in the human stomach. Enterohepatic Helicobacter spp. induce inflammatory bowel disease and colorectal carcinoma in susceptible mouse strains, permitting study of host immunity and microbial factors at the cellular and molecular level. H. hepaticus is the only proven infectious hepatocarcinogen of mice and has been used to explore mechanisms of inflammation-associated liver cancer as seen in human chronic viral hepatitis. For example, this model was used to identify for the first time a potential mechanism for male-predominant liver cancer risk independent of circulating sex hormones. Helicobacter-based mouse models of digestive system carcino-genesis are used to investigate the basic biology of inflammation-associated human cancers and to evaluate therapeutic interventions at the discovery level. Because of exciting advances in genetic engineering of mice, in vivo imaging, and system-wide genomics and proteomics, these models will provide even more information in the future. This chapter introduces the mouse as a model species; summarizes important models of inflammation-associated cancer incited by murine Helicobacter infection; and describes methods for the collection, sampling, and histologic grading of mouse digestive system tissues.

CpG motifs of bacterial DNA exert protective effects in mouse models of IBD by antigen-independent tolerance induction

BACKGROUND & AIMS

Prophylactic treatment of mice with CpG motifs of bacterial DNA protects from experimental inflammatory bowel disease, at least partly via induction of inhibitory T-cells. The aim of this study was to elucidate whether these CpG-dependent protective effects require presence of bacterial flora suggesting antigen-specific regulatory activity.

METHODS

Germ-free BALB/c and IL-10(-/-) mice were treated with CpG-oligodeoxynucleotides (ODN), control-ODN, or PBS. CD4(+)CD62L(+) cells of these mice were transferred into SCID recipients. CpG-ODN-treated germ-free IL-10(-/-) mice were transferred into colitogenic environment. Monoclonal antibodies were used to neutralize TGF-beta and IFN-alpha/beta during CpG-ODN treatment. CD4(+)CD62L(+) cells of donors were evaluated for cytokine secretion and FOXP3, PD-1, and CD25 expression.

RESULTS

Compared to PBS or control-ODN treatment, CpG-ODN application to germ-free donors led to decreased intestinal inflammation as indicated by histology, decreased proinflammatory cytokines, and increased IL-10 secretion. Protection was also observed after cotransfer of cells from PBS and CpG-ODN treated donors. Anti-TGF-beta and anti-INF-alpha/beta partly reversed the protective CpG-ODN effect. CpG-ODN-treated germ-free IL-10(-/-) mice transferred into colitogenic environment developed significantly less colitis than controls but not recipients of IL-10(-/-)CD4(+)CD62L(+)cells. CD4(+)CD62L(+)cells of CpG-treated germ-free animals displayed increased expression of regulatory markers.

CONCLUSIONS

Even without pre-existence of bacterial flora CpG-ODN exposition induces tolerance, indicating that CpG-ODN-induced regulatory T-cells are not bacterial antigen specific. TGF-beta and IFN-alpha/beta play major roles in induction of regulatory cells, and although IL10-independent mechanisms play a role in CpG-ODN protection, this cytokine likely is important for the effector mechanism of CpG-ODN-induced regulatory T-cells.

Probiotic and prebiotic influence beyond the intestinal tract

Probiotics and prebiotics have long been appreciated for their positive influences on gut health. Research on the mechanisms and effects of these agents shows that their impact reaches beyond the intestine. Effects on the microecology and pathology of the oral cavity, stomach, and vaginal tract have been observed. Likely mediated through immune influences, systemic effects such as reduced severity of colds or other respiratory conditions, impact on allergy incidence and symptoms, and reduced absences from work or daycare have also been noted. These observations, among others, suggest a broader spectrum of influence than commonly considered for these unique substances.

Sensitivity to Escherichia coli Nissle 1917 in mice is dependent on environment and genetic background

Escherichia coli Nissle 1917 (EcN) is a well-characterized probiotic bacterium. Although genomic comparisons of EcN with the uropathogenic E. coli strain CFT073 revealed high degrees of similarity, EcN is generally considered a non-pathogenic organism. However, as recent evidence suggests that EcN is capable of inducing inflammatory responses in host intestinal epithelial cells, we aimed to investigate potential pathogenic properties of EcN in an in vivo model using various germ-free (GF) mouse strains. With the exception of C3H/HeJZtm mice, which carry a defective toll-like receptor (TLR)4-allele, no lesions were obvious in mice of different strains orally inoculated with EcN for 1 week, although organ cultures (blood, lung, mesenteric lymph node, pancreas, spleen, liver and kidney) tested positive to various degrees. C3H/HeJZtm mice inoculated with EcN became clinically ill and the majority died or had to be euthanized. Organs of all gnotobiotic C3H/HeJZtm mice were positive for EcN by culture; major histological findings were moderate to severe pyogranulomatous serositis, typhlitis and pancreatitis. Histological findings were corroborated by highly elevated tumour necrosis factor (TNF) serum levels. Lesions were not detected in specified pathogen free maintained C3H/HeJZtm mice, GF C3H/HeJ mice lacking the interleukin-10 gene, or GF C3H/HeJZtm mice that were inoculated with E. coli K12 strain MG1655 as a control. In addition, mild histological lesions were detected in Ztm:NMRI mice 3 months after oral inoculation with EcN. This study shows that EcN is capable of displaying a virulent phenotype in GF C3H/HeJZtm mice. Whether this phenotype is linked to the bacterium's probiotic nature should be the focus of further studies.

Microbial diversity of inflamed and noninflamed gut biopsy tissues in inflammatory bowel disease

BACKGROUND

Inflammatory bowel disease (IBD) is a chronic gastrointestinal condition without any known cause or cure. An imbalance in normal gut biota has been identified as an important factor in the inflammatory process.

METHODS

Fifty-eight biopsies from Crohn's disease (CD, n = 10), ulcerative colitis (UC, n = 15), and healthy controls (n = 16) were taken from a population-based case-control study. Automated ribosomal intergenic spacer analysis (ARISA) and terminal restriction fragment length polymorphisms (T-RFLP) were used as molecular tools to investigate the intestinal microbiota in these biopsies.

RESULTS

ARISA and T-RFLP data did not allow a high level of clustering based on disease designation. However, if clustering was done based on the inflammation criteria, the majority of biopsies grouped either into inflamed or noninflamed groups. We conducted statistical analyses using incidence-based species richness and diversity as well as the similarity measures. These indices suggested that the noninflamed tissues form an intermediate population between controls and inflamed tissue for both CD and UC. Of particular interest was that species richness increased from control to noninflamed tissue, and then declined in fully inflamed tissue.

CONCLUSIONS

We hypothesize that there is a recruitment phase in which potentially pathogenic bacteria colonize tissue, and once the inflammation sets in, a decline in diversity occurs that may be a byproduct of the inflammatory process. Furthermore, we suspect that a better knowledge of the microbial species in the noninflamed tissue, thus before inflammation sets in, holds the clues to the microbial pathogenesis of IBD.