Analyses of human colonic mucus obtained by an in vivo sampling technique

Fecal microbiota transplantation for managing irritable bowel syndrome

Irritable bowel syndrome (IBS) is a widespread gastrointestinal disorder affecting 11.2% of the world adult population. The intestinal microbiome is thought to play a pivotal role in the pathophysiology of IBS. The composition of the fecal microbiome in IBS patients differs from that in healthy individuals, but the exact bacteria species involved in the development of IBS remain to be determined. There is also an imbalance between useful and harmful bacteria (dysbiosis) in the intestinal microbiome in patients with IBS. Consuming prebiotics, probiotics, or synbiotics has a limited effect on IBS symptoms. In contrast, fecal microbiome transplantation (FMT) in IBS patients reverses the dysbiosis to normobiosis and reduces the IBS symptoms in about 70% of patients, and is not associated with any serious adverse events. Area covered: The available data on the microbiome and FMT in IBS regarding the efficacy of FMT in managing IBS were found using a PubMed search of these topics. Expert commentary: FMT is a promising tool for managing irritable syndrome. It appears to be effective, easy, and inexpensive procedure. However, more controlled studies involving larger cohorts of IBS are needed before FMT can be used as a routine procedure in the clinic.

Dietary fiber in irritable bowel syndrome (Review)

Irritable bowel syndrome (IBS) is a common chronic gastrointestinal disorder. It is widely believed that IBS is caused by a deficient intake of dietary fiber, and most physicians recommend that patients with IBS increase their intake of dietary fiber in order to relieve their symptoms. However, different types of dietary fiber exhibit marked differences in physical and chemical properties, and the associated health benefits are specific for each fiber type. Short-chain soluble and highly fermentable dietary fiber, such as oligosaccharides results in rapid gas production that can cause abdominal pain/discomfort, abdominal bloating/distension and flatulence in patients with IBS. By contrast, long-chain, intermediate viscous, soluble and moderately fermentable dietary fiber, such as psyllium results in a low gas production and the absence of the symptoms related to excessive gas production. The effects of type of fiber have been documented in the management of IBS, and it is known to improve the overall symptoms in patients with IBS. Dietary fiber acts on the gastrointestinal tract through several mechanisms, including increased fecal mass with mechanical stimulation/irritation of the colonic mucosa with increasing secretion and peristalsis, and the actions of fermentation byproducts, particularly short-chain fatty acids, on the intestinal microbiota, immune system and the neuroendocrine system of the gastrointestinal tract. Fiber supplementation, particularly psyllium, is both safe and effective in improving IBS symptoms globally. Dietary fiber also has other health benefits, such as lowering blood cholesterol levels, improving glycemic control and body weight management.

Dismicrobism in inflammatory bowel disease and colorectal cancer: Changes in response of colocytes

Patients with inflammatory bowel disease (IBD) have an increased risk of 10%-15% developing colorectal cancer (CRC) that is a common disease of high economic costs in developed countries. The CRC has been increasing in recent years and its mortality rates are very high. Multiple biological and biochemical factors are responsible for the onset and progression of this pathology. Moreover, it appears absolutely necessary to investigate the environmental factors favoring the onset of CRC and the promotion of colonic health. The gut microflora, or microbiota, has an extensive diversity both quantitatively and qualitatively. In utero, the intestine of the mammalian fetus is sterile. At birth, the intestinal microbiota is acquired by ingesting maternal anal or vaginal organisms, ultimately developing into a stable community, with marked variations in microbial composition between individuals. The development of IBD is often associated with qualitative and quantitative disorders of the intestinal microbial flora (dysbiosis). The healthy human gut harbours about 10 different bacterial species distributed in colony forming units which colonize the gastrointestinal tract. The intestinal microbiota plays a fundamental role in health and in the progression of diseases such as IBD and CRC. In healthy subjects, the main control of intestinal bacterial colonization occurs through gastric acidity but other factors such as endoluminal temperature, competition between different bacterial strains, peristalsis and drugs can influence the intestinal microenvironment. The microbiota exerts diverse physiological functions to include: growth inhibition of pathogenic microorganisms, synthesis of compounds useful for the trophism of colonic mucosa, regulation of intestinal lymphoid tissue and synthesis of amino acids. Furthermore, mucus seems to play an important role in protecting the intestinal mucosa and maintaining its integrity. Changes in the microbiota composition are mainly influenced by diet and age, as well as genetic factors. Increasing evidence indicates that dysbiosis favors the production of genotoxins and metabolites associated with carcinogenesis and induces dysregulation of the immune response which promotes and sustains inflammation in IBD leading to carcinogenesis. A disequilibrium in gut microflora composition leads to the specific activation of gut associated lymphoid tissue. The associated chronic inflammatory process associated increases the risk of developing CRC. Ulcerative colitis and Crohn’s disease are the two major IBDs characterized by an early onset and extraintestinal manifestations, such as rheumatoid arthritis. The pathogenesis of both diseases is complex and not yet fully known. However, it is widely accepted that an inappropriate immune response to microbial flora can play a pivotal role in IBD pathogenesis.

Antimicrobial peptides and the enteric mucus layer act in concert to protect the intestinal mucosa

The intestinal mucosa squares the circle by allowing efficient nutrient absorption while generating a firm barrier toward the enteric microbiota, enteropathogenic microorganisms and high luminal concentrations of potent immunostimulatory molecules. The mucus layer together with local antimicrobial and anti-inflammatory peptides significantly contribute to this ability. Here we summarize the recent progress made to better understand the critical importance of this dynamic, complex and highly structured anti-inflammatory and antimicrobial barrier.

Structural basis for adaptation of lactobacilli to gastrointestinal mucus

The mucus layer covering the gastrointestinal (GI) epithelium is critical in selecting and maintaining homeostatic interactions with our gut bacteria. However, the underpinning mechanisms of these interactions are not understood. Here, we provide structural and functional insights into the canonical mucus-binding protein (MUB), a multi-repeat cell-surface adhesin found in Lactobacillus inhabitants of the GI tract. X-ray crystallography together with small-angle X-ray scattering demonstrated a 'beads on a string' arrangement of repeats, generating 174 nm long protein fibrils, as shown by atomic force microscopy. Each repeat consists of tandemly arranged Ig- and mucin-binding protein (MucBP) modules. The binding of full-length MUB was confined to mucus via multiple interactions involving terminal sialylated mucin glycans. While individual MUB domains showed structural similarity to fimbrial proteins from Gram-positive pathogens, the particular organization of MUB provides a structural explanation for the mechanisms in which lactobacilli have adapted to their host niche by maximizing interactions with the mucus receptors, potentiating the retention of bacteria within the mucus layer. Together, this study reveals functional and structural features which may affect tropism of microbes across mucus and along the GI tract, providing unique insights into the mechanisms adopted by commensals and probiotics to adapt to the mucosal environment.

More than a marine propeller--the flagellum of the probiotic Escherichia coli strain Nissle 1917 is the major adhesin mediating binding to human mucus

The flagellum of the probiotic Escherichia coli strain Nissle 1917 (EcN) is not just responsible for motility, but also for EcN's ability to induce the production of human β-defensin 2. Here, we report a third function of this EcN organell. In this study we investigated the role of the EcN flagellum in adhesion to different host tissues by ex vivo and in vitro studies. Ex vivo studies with cryosections of human gut biopsies revealed that the flagellum of EcN is most likely important for efficient adhesion to the human intestinal tract. These results and in vitro studies with different epithelial cells indicated that the presence of mucus is important for efficient mediation of adhesion by the flagellum of EcN. We observed direct interaction between isolated flagella from EcN wild type and porcine mucin 2 as well as human mucus. However, we could not observe any interaction of the flagella with murine mucus. For the first time, we identified the mucus component gluconate as one receptor for the binding of flagella from EcN and were able to exclude the flagellin domain D3 as a responsible interaction partner. We propose that the flagellum of EcN is its major adhesin in vivo, which enables this probiotic strain to compete efficiently for binding sites on host tissue with several bacterial pathogens.

Human faecal microbiota display variable patterns of glycerol metabolism

Significant amounts of glycerol reach the colon microbiota daily through the diet and/or by in situ microbial production or release from desquamated epithelial cells. Some gut microorganisms may anaerobically reduce glycerol to 1,3-propanediol (1,3-PDO), with 3-hydroxypropanal as an intermediate. Accumulation of the latter intermediate may result in the formation of reuterin, which is known for its biological activity (e.g. antimicrobial properties). To date, glycerol metabolism in mixed cultures from the human colon has received little attention. Using in vitro batch incubations of faeces from 10 human individuals, we demonstrated that glycerol addition (140 mM) significantly affects the metabolism and composition of the microbial community. About a third of the samples exhibited rapid glycerol conversion, yielding proportionally higher levels of acetate and 1,3-PDO. In contrast, a slower glycerol metabolism resulted in higher levels of propionate. Furthermore, rapid glycerol metabolism correlated with significant shifts in the Lactobacillus-Enterococcus community, which were not observed in slower glycerol-metabolizing samples. As the conversion of glycerol to 1,3-PDO is a highly reducing process, we infer that the glycerol metabolism may act as an effective hydrogen sink. Given the importance of hydrogen-consuming processes in the gut, this work suggests that glycerol may have potential as a tool for modulating fermentation kinetics and profiles in the gastrointestinal tract.