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.

Cellulose-degrading microorganisms involved in the breakdown of plant cell wall material in the human gut remain rather unexplored despite their role in intestinal fermentation. Microcrystalline cellulose-degrading bacteria were previously identified in faeces of methane-excreting individuals, whereas these microorganisms were undetectable in faecal samples from non-methane excretors. This suggested that the structure and activity of the cellulose-degrading community differ in methane- and non-methane-excreting individuals. The purpose of this study was to characterize in depth this cellulose-degrading community in individuals of both CH(4) statuses using both culture-dependent and molecular methods. A new real-time PCR analysis was developed to enumerate microcrystalline cellulose-degrading ruminococci and used to confirm the predominance of these hydrolytic ruminococci in methane excretors. Culture-dependent methods using cell wall spinach (CWS) residue revealed the presence of CWS-degrading microorganisms in all individuals. Characterization of CWS-degrading isolates further showed that the main cellulose-degrading bacteria belong essentially to Bacteroidetes in non-methane-excreting subjects, while they are predominantly represented by Firmicutes in methane-excreting individuals. This taxonomic diversity was associated with functional diversity: the ability to degrade different types of cellulose and to produce H(2) from fermentation differed depending on the species. The structure of the cellulolytic community was shown to vary depending on the presence of methanogens in the human gut.

A strictly anaerobic, cellulolytic strain, designated 18P13 T , was isolated from a human faecal sample. Cells were Gram-positive non-motile cocci. Strain 18P13 T was able to degrade microcrystalline cellulose but the utilization of soluble sugars was restricted to cellobiose. Acetate and succinate were the major end products of cellulose and cellobiose fermentation. 16S rRNA gene sequence analysis revealed that the isolate belonged to the genus Ruminococcus of the family Ruminococcaceae. The closest phylogenetic relative was the ruminal cellulolytic strain Ruminococcus flavefaciens ATCC 19208 T (,95 % 16S rRNA gene sequence similarity). The DNA G+C content of strain 18P13 T was 53.05±0.7 mol%. On the basis of phylogenetic analysis, and morphological and physiological data, strain 18P13 T can be differentiated from other members of the genus Ruminococcus with validly published names. The name Ruminococcus champanellensis sp. nov. is proposed, with 18P13 T (5DSM 18848 T 5JCM 17042 T ) as the type strain.The human large intestine harbours a large diversity of bacterial communities that play a key role in health and disease through their involvement in nutrition, pathogenesis and immunology (Cummings & Macfarlane, 1991;Salminen et al., 1998). A proper understanding of the diversity and functionality of species in the human gut ecosystem is therefore of considerable importance. Over the past 20 years, the microbiota composition has been investigated using both culture-and molecular-based methods and results have revealed the extensive diversity of this ecosystem (Eckburg et al., 2005;Chassard et al., 2008b;Qin et al., 2010). The microbiota is mainly composed of bacteria belonging to three major phyla: 'Bacteroidetes', 'Firmicutes' and 'Actinobacteria'. The genus Ruminococcus represents an important phylogenetic taxon, belonging to phylum 'Firmicutes', and corresponds to 5-15 % of the total bacterial population in the colon (Chassard et al., 2008b; Ramirez-Farias et al., 2009).Presently, the genus Ruminococcus is not monophyletic and is divided into two phylogenetically separate groups.Group I is located within rRNA cluster IV and includes Ruminococcus flavefaciens, the type species of the genus. In the latest edition of Bergey's Manual of Systematic Bacteriology, members of group I were included in the family Ruminococcaceae and should be considered as Ruminococcus sensu stricto (Rainey, 2009a). Members of group II are located within rRNA cluster XIVa, which is now recognized as the family Lachnospiraceae, a large group of phenotypic and phylogenetic heterogeneous genera (Rainey, 2009b). Recently, a number of misclassified Ruminococcus species and a Clostridium species in group II were reclassified in the genus Blautia (Liu et al., 2008). The remaining ruminococci within group II most likely constitute the nuclei of novel genera and should not be considered true ruminococci.The genus Ruminococcus comprises anaerobic Grampositive cocci with a fermentative metabolism for which carbohydrates, but not amino acids, serve...

During the course of a study on the xylan-degrading community from the human gut, six xylanolytic, Gram-negative, anaerobic rods were isolated from faecal samples. 16S rRNA gene sequence analysis showed that the isolates were closely related to each other (¢99 % sequence similarity) and that they belonged to the genus Bacteroides. On the basis of 16S rRNA gene sequence similarity, representative strain XB1AT was most closely related to the type strains ofBacteroides ovatus (97.5 %), B. finegoldii (96.5 %) and B. thetaiotaomicron (95.5 %). DNA-DNA hybridization results revealed that strain XB1A T was distinct from its closest relative, B. ovatus.The DNA G+C content of strain XB1A T (42.8 mol%) and major fatty acid composition (anteiso-C 15 : 0 , 33.8 %) further supported its affiliation to the genus Bacteroides. The novel isolates degraded different types of xylan, and were also able to grow on a variety of carbohydrates. Unlike most other Bacteroides species isolated from the human gut, these isolates were not able to degrade starch. Other biochemical tests further demonstrated that strain XB1A T could be differentiated from the closest related Bacteroides species. Xylan and sugars were converted by strain XB1A T mainly into acetate, propionate and succinate. Based on physiological, phenotypic and phylogenetic data, the six novel strains are considered to represent a novel species of the genus Bacteroides, for which the name Bacteroides xylanisolvens sp. nov. is proposed. The type strain is XB1A T (5DSM 18836 T 5CCUG 53782 T ).

The intestinal microbiota of patients with constipated-predominant irritable bowel syndrome (C-IBS) displays chronic dysbiosis. Our aim was to determine whether this microbial imbalance instigates perturbation of the host intestinal mucosal immune response, using a model of human microbiota-associated rats (HMAR) and dextran sulfate sodium (DSS)-induced experimental colitis. The analysis of the microbiota composition revealed a decrease of the relative abundance of Bacteroides, Roseburia-Eubacterium rectale and Bifidobacterium and an increase of Enterobacteriaceae, Desulfovibrio sp., and mainly Akkermansia muciniphila in C-IBS patients compared to healthy individuals. The bacterial diversity of the gut microbiota of healthy individuals or C-IBS patients was maintained in corresponding HMAR. Animals harboring a C-IBS microbiota had reduced DSS colitis with a decreased expression of pro-inflammatory cytokines from innate, Th1, and Th17 responses. The pre-treatment of conventional C57BL/6 mice or HMAR with A. muciniphila, but not with Escherichia coli, prior exposure to DSS also resulted in a reduction of colitis severity, highlighting that the anti-inflammatory effect of the gut microbiota of C-IBS patients is mediated, in part, by A. muciniphila. This work highlights a novel aspect of the crosstalk between the gut microbiota of C-IBS patients and host intestinal homeostasis.