This review explores our current understanding of the complex interaction between environmental risk factors, genetic traits and the development of inflammatory bowel disease. The primacy of environmental risk factors is illustrated by the rapid increase in the incidence of the disease worldwide. We discuss how the gut microbiota is the proximate environmental risk factor for subsequent development of inflammatory bowel disease. The evolving fields of virome and mycobiome studies will further our understanding of the full potential of the gut microbiota in disease pathogenesis. Manipulating the gut microbiota is a promising therapeutic avenue.

BackgroundOverweight and metabolic problems now add to the burden of illness in patients with Inflammatory Bowel Disease. We aimed to determine if a program of aerobic and resistance exercise could safely achieve body composition changes in patients with Inflammatory Bowel Disease.MethodsA randomized, cross-over trial of eight weeks combined aerobic and resistance training on body composition assessed by Dual Energy X-ray Absorptiometry was performed. Patients in clinical remission and physically inactive with a mean age of 25 ± 6.5 years and Body Mass Index of 28.9 ± 3.8 were recruited from a dedicated Inflammatory Bowel Disease clinic. Serum cytokines were quantified, and microbiota assessed using metagenomic sequencing.ResultsImproved physical fitness was demonstrated in the exercise group by increases in median estimated VO2max (Baseline: 43.41mls/kg/min; post-intervention: 46.01mls/kg/min; p = 0.03). Improvement in body composition was achieved by the intervention group (n = 13) with a median decrease of 2.1% body fat compared with a non-exercising group (n = 7) (0.1% increase; p = 0.022). Lean tissue mass increased by a median of 1.59 kg and fat mass decreased by a median of 1.52 kg in the exercising group. No patients experienced a deterioration in disease activity scores during the exercise intervention. No clinically significant alterations in the α- and β-diversity of gut microbiota and associated metabolic pathways were evident.ConclusionsModerate-intensity combined aerobic and resistance training is safe in physically unfit patients with quiescent Inflammatory Bowel Disease and can quickly achieve favourable body compositional changes without adverse effects.Trial registrationThe study was registered at ClinicalTrials.gov; Trial number: NCT02463916.Electronic supplementary materialThe online version of this article (10.1186/s12876-019-0952-x) contains supplementary material, which is available to authorized users.

ObjectiveThe microbiome contributes to the pathogenesis of inflammatory bowel disease (IBD) but the relative contribution of different lifestyle and environmental factors to the compositional variability of the gut microbiota is unclear.DesignHere, we rank the size effect of disease activity, medications, diet and geographic location of the faecal microbiota composition (16S rRNA gene sequencing) in patients with Crohn’s disease (CD; n=303), ulcerative colitis (UC; n = 228) and controls (n=161), followed longitudinally (at three time points with 16 weeks intervals).ResultsReduced microbiota diversity but increased variability was confirmed in CD and UC compared with controls. Significant compositional differences between diseases, particularly CD, and controls were evident. Longitudinal analyses revealed reduced temporal microbiota stability in IBD, particularly in patients with changes in disease activity. Machine learning separated disease from controls, and active from inactive disease, when consecutive time points were modelled. Geographic location accounted for most of the microbiota variance, second to the presence or absence of CD, followed by history of surgical resection, alcohol consumption and UC diagnosis, medications and diet with most (90.3%) of the compositional variance stochastic or unexplained.ConclusionThe popular concept of precision medicine and rational design of any therapeutic manipulation of the microbiota will have to contend not only with the heterogeneity of the host response, but also with widely differing lifestyles and with much variance still unaccounted for.

Studies of inflammatory bowel disease (IBD) have been inconclusive in relating microbiota with distribution of inflammation. We report microbiota, host transcriptomics, epigenomics and genetics from matched inflamed and non-inflamed colonic mucosa [50 Crohn's disease (CD); 80 ulcerative colitis (UC); 31 controls]. Changes in community-wide and within-patient microbiota are linked with inflammation, but we find no evidence for a distinct microbial diagnostic signature, probably due to heterogeneous host-microbe interactions, and show only marginal microbiota associations with habitual diet. Epithelial DNA methylation improves disease classification and is associated with both inflammation and microbiota composition. Microbiota sub-groups are driven by dominant Enterbacteriaceae and Bacteroides species, representative strains of which are pro-inflammatory in vitro, are also associated with immune-related epigenetic markers. In conclusion, inflamed and non-inflamed colonic segments in both CD and UC differ in microbiota composition and epigenetic profiles.

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BackgroundAlteration of the gut microbiota by repeated antibiotic treatment increases susceptibility to Clostridioides difficile infection. Faecal microbiota transplantation from donors with a normal microbiota effectively treats C. difficile infection.MethodsThe study involved 10 patients with recurrent C. difficile infection, nine of whom received transplants from individual donors and one who received a donor unit from a stool bank (OpenBiome).ResultsAll individuals demonstrated enduring post-transplant resolution of C. difficile- associated diarrhoea. Faecal microbiota diversity of recipients significantly increased, and the composition of the microbiota resembled that of the donor. Patients with C. difficile infection exhibited significantly lower faecal levels of secondary/ bile acids and higher levels of primary bile acids. Levels of secondary bile acids were restored in all transplant recipients, but to a lower degree with the OpenBiome transplant. The abundance increased of bacterial genera known from previous studies to confer resistance to growth and germination of C. difficile. These were significantly negatively associated with primary bile acid levels and positively related with secondary bile acid levels. Although reduced levels of the short chain fatty acids, butyrate, propionate and acetate, have been previously reported, here we report elevations in SCFA, pyruvic and lactic fatty acids, saturated, ω-6, monounsaturated, ω-3 and ω-6 polyunsaturated fatty acids (PUFA) in C. difficile infection. This potentially indicates one or a combination of increased dietary FA intake, microbial modification of FAs or epithelial cell damage and inflammatory cell recruitment. No reversion to donor FA profile occurred post-FMT but ω-3 to ω-6 PUFA ratios were altered in the direction of the donor. Archaeal metabolism genes were found in some samples post FMT.ConclusionA consistent metabolic signature was identified in the post-transplant microbiota, with reduced primary bile acids and substantial restoration of secondary bile acid production capacity. Total FA levels were unchanged but the ratio of inflammatory to non-inflammatory FAs decreased.Electronic supplementary materialThe online version of this article (10.1186/s12876-018-0860-5) contains supplementary material, which is available to authorized users.

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