Effects of scFOS on the composition of fecal microbiota and anxiety in patients with irritable bowel syndrome: a randomized, double blind, placebo controlled study.

BACKGROUND: Short-chain fructooligosaccharides (scFOS) have beneficial effects in subjects with minor digestive complaints, but the potential mechanisms involved have not been elucidated. The aim of the study was to evaluate changes in rectal sensitivity related to the clinical effects of scFOS in a selected group of patients with irritable bowel syndrome (IBS) and rectal hypersensitivity. METHODS: In 79 IBS patients (defined by Rome III criteria) with rectal hypersensitivity (defined as discomfort threshold ≤44 g) a parallel, placebo-controlled, randomized, and double-blind study was performed to assess the effects of dietary supplementation (5 g d-1 ) with scFOS vs placebo for 4 weeks on rectal sensitivity (primary outcome: tolerance to increasing wall tension applied by a tensostat), clinical outcomes (IBS, anxiety/depression and quality of life scores) and composition of fecal microbiota. KEY RESULTS: Rectal discomfort threshold, and IBS and quality of life scores, significantly improved during treatment, but in a similar manner in both scFOS and placebo groups; a post-hoc analysis showed that the effect of scFOS on rectal sensitivity was more pronounced in constipation-predominant-IBS patients (P=.051 vs placebo). Contrary with placebo, scFOS significantly reduced anxiety scores and increased fecal Bifidobacteria (P<.05 for both) without modifying other bacterial groups. CONCLUSIONS & INTERFENCES: The effect of scFOS on anxiety may be related to modulation of the gut microbiota; demonstration of effects of scFOS on rectal sensitivity may require higher doses and may depend on the IBS subgroup.

The hypersensitivity to colonic distension of IBS patients can be transferred to rats through their fecal microbiota.

BACKGROUND: Alterations of intestinal microbiota and hypersensitivity to colonic distension are two features of the irritable bowel syndrome (IBS). However, the role of intestinal microbiota in visceral hypersensitivity of IBS patients is far to be established. The aim of our study was to determine whether the intestinal microbiota is involved in the visceral hypersensitivity in IBS. METHODS: The painful response to colorectal distension and colonic mucosal parameters were assessed in gnotobiotic rats. Germfree (GF) rats were inoculated with the fecal microbiota from IBS patients characterized by hypersensitivity to colorectal distension (IBS HMA rats) or from non-hypersensitive healthy volunteers (Healthy HMA rats). Conventional rats were studied as normosensitivity control. Fecal microbial analyses were carried out in human and HMA rats fecal samples using cultural and molecular approaches. KEY RESULTS: The microbial dysbiosis of the IBS gut microbiota (more sulfate-reducing bacteria and Enterobacteriaceae and less bifidobacteria) could be maintained in gnotobiotic rats. The number of abdominal contractions in response to colorectal distensions was significantly higher in IBS HMA rats than in healthy HMA rats. No difference was observed between healthy HMA and conventional rats. Colorectal compliance, epithelial paracellular permeability, and density of colonic mucosal mast cells were similar in the three groups of rats. CONCLUSIONS & INFERENCES: We herein showed that sensitivity to colonic distension of IBS patients can be transferred to rats by the fecal microbiota. Mucosal alterations associated with microbiota transfer are not involved in this hypersensitivity. The altered IBS microbiota may have important role in the hypersensitivity characterizing IBS patients through specific bacterial metabolites.

Functional dysbiosis within the gut microbiota of patients with constipated-irritable bowel syndrome.

BACKGROUND: The role of the gut microbiota in patho-physiology of irritable bowel syndrome (IBS) is suggested by several studies. However, standard cultural and molecular methods used to date have not revealed specific and consistent IBS-related groups of microbes. AIM: To explore the constipated-IBS (C-IBS) gut microbiota using a function-based approach. METHODS: The faecal microbiota from 14 C-IBS women and 12 sex-match healthy subjects were examined through a combined strictly anaerobic cultural evaluation of functional groups of microbes and fluorescent in situ hybridisation (16S rDNA gene targeting probes) to quantify main groups of bacteria. Starch fermentation by C-IBS and healthy faecal samples was evaluated in vitro. RESULTS: In C-IBS, the numbers of lactate-producing and lactate-utilising bacteria and the number of H(2) -consuming populations, methanogens and reductive acetogens, were at least 10-fold lower (P < 0.05) compared with control subjects. Concomitantly, the number of lactate- and H(2) -utilising sulphate-reducing population was 10 to 100 fold increased in C-IBS compared with healthy subjects. The butyrate-producing Roseburia - E. rectale group was in lower number (0.01 < P < 0.05) in C-IBS than in control. C-IBS faecal microbiota produced more sulphides and H(2) and less butyrate from starch fermentation than healthy ones. CONCLUSIONS: A major functional dysbiosis was observed in constipated-irritable bowel syndrome gut microbiota, reflecting altered intestinal fermentation. Sulphate-reducing population increased in the gut of C-IBS and were accompanied by alterations in other microbial groups. This could be responsible for changes in the metabolic output and enhancement in toxic sulphide production which could in turn influence gut physiology and contribute to IBS pathogenesis.

[Fermentative metabolism by the human gut microbiota]. / Activités métaboliques du microbioteintestinal humain.

The human large intestine is colonized by a complex community of microorganisms, largely composed of strictly anaerobic bacteria with numerous physiological functions which impact on the host nutrition and health. Among these functions, the fermentation of substrates is of major importance for host health through the production of a wide variety of metabolites. The metabolic functions of the human gut microbiota are correlated with the nature of the substrates available for fermentation in the colon. These substrates are from exogenous (dietary fibers that are mainly plant polysaccharides) and endogenous (produced by the host and represent important source of nitrogen) sources. The metabolites produced from the microbial fermentation process in the gut are mainly absorbed and used by the host. Most of them have health benefits, but some may also have deleterious effects. The gut microbiota should thus be considered in relation to its environment, including dietary food and host factors. The interactions between food, intestinal microbiota and the host are fundamental to the maintenance of homeostasis in the ecosystem. Any disruption of this equilibrium could modify the functionality of the gut microbiota and lead to a pathological state.

Dietary fibre degradation and fermentation by two xylanolytic bacteria Bacteroides xylanisolvens XB1A and Roseburia intestinalis XB6B4 from the human intestine.

AIMS: To characterize fibre degradation, colonization and fermentation, and xylanase activity of two xylanolytic bacteria Bacteroides xylanisolvens XB1A(T) and Roseburia intestinalis XB6B4 from the human colon. METHODS AND RESULTS: The bacteria grew well on all the substrates chosen to represent dietary fibres: wheat and corn bran, pea, cabbage and leek fibres, and also on purified xylans. Roseburia intestinalis colonized the substrates more efficiently than Bact. xylanisolvens. For the two bacteria, 80-99% of the total xylanase activity was associated with the cells whatever the substrate and time of growth. Optimal specific activities of cells were obtained on oat spelt xylan; they were higher than those previously measured for xylanolytic bacteria from the human gut. Roseburia intestinalis produced high molecular mass xylanases (100-70 kDa), while Bact. xylanisolvens produced lower molecular mass enzymes, including a cell-associated xylanase of 37 kDa. CONCLUSIONS: The two bacteria display very high xylanolytic activity on the different substrates. Differences were observed on substrate attachment and enzyme systems, suggesting that the two species occupy different niches within the gut microbiota. SIGNIFICANCE AND IMPACT OF THE STUDY: This study characterizes xylan degradation by two major species of the human intestine.

Interspecies H2 transfer in cellulose degradation between fibrolytic bacteria and H2-utilizing microorganisms from the human colon.

Interspecies H2 transfer between two newly isolated fibrolytic strains (18P13 and 18P16) and H2-utilizing methanogen or acetogen from the human colon was investigated during in vitro cellulose degradation. Both H2-consuming microorganisms utilized efficiently H2 produced from cellulose fermentation by the fibrolytic species. H2 utilization by Methanobrevibacter smithii did not change the metabolism and the cellulolytic activity of strain 18P16 whereas it induced a metabolic shift in strain 18P13. However, this metabolic shift was not associated with enhancement of cellulose degradation. In contrast, an increase in cellulose breakdown was observed when strain 18P13 was cultivated with Ruminococcus hydrogenotrophicus. This stimulating effect could be attributed to both the autotrophic and the heterotrophic metabolism of the acetogen in the coculture.