Microbial Flora and Digestive Disease
V. Stanghellini

University of Bologna, Department of Clinical Medicine University of Bologna, Bologna Italy
Gut microbiota consists of the microorganisms thatinhabit the alimentary canal.  The microorganisms inhabiting the gut lumen are essential for gut homeostasis. Specifically, they interact with the intestinal immune system, supply key nutrients for the major components of the gut wall, and modulate energy metabolism. Laboratory animals grown in germ free conditions have poor development of the gut immune system, immature gastrointestinal motor patterns, reduced micronutrient absorption and increased susceptibility to infections. Host–microbiome interactions can be either beneficialor deleterious, driving gastrointestinallymphoid tissue activities and shaping gut wall structures. Modifications of the complex interplay between gut microbiota and relative responses of the gastrointestinal tract may play a potential role in in the determinism of important pathological conditions such as the irritable bowel syndrome (IBS), inflammatory bowel diseases (IBD) and colorectal cancer. The intestinal microbiota isacquired at birth but changes rapidly during the first yearof life. In adults, each person's unique population of fecalmicrobiota is fairly stable over time, but fluctuations occurin response to environmental, developmental and pathological events.Host–microbiome interactions can be mutually beneficialor can be deleterious, inciting intestinal inflammation. The intestinal epithelium at the interface between the intestinalmicrobiome and the lymphoid tissue associated with the gastrointestinalsystem plays a critical role in shaping the mucosal immune response.Intestinal epithelial cells are a physical barrier against excessiveentry of bacteria and other antigens from the intestinal lumeninto the circulation. An intact mucosal barrier depends on intercellularjunctions, which help to seal the the paracellular space.Our understanding of phylogenetic composition of human intestinal microbiota and molecular as well as metabolic patterns underlying host-microbial interactions has remarkably grown in the last decade, by virtue of the development and application of novel high throughput molecular techniques. Nonetheless, we have concomitantly appreciated that the unfolding intestinal microbiota secrets is hampered by the complexity of the human intestinal ecosystem and by limitations of currently available methods. In this respect current understanding of what should be considered a “normal flora” is still elementary despite recent adavances in bacterial identification and characterization.These boundaries become important when interpreting the data on the participation of intestinal microbiota in the pathophysiology of pathological conditions of the alimentary canal including the irritable bowel syndrome (IBS), inflammatory bowel diseases (IBD) and colorectal cancer. Thus, a major overlap between gastroenterology and microbiology is emerging, with important therapeutic implications.   The importance of non digestible polysaccharides  that serve as metabolic substrates for subsets on intestinal microbiota in inducing a slightly acidic colonic environment through the production of slow chain fatty acids is now better understood.  Butyrate in particular enhances cellular differentiation and limits proliferation. Butyrate and probiotic  treatments can independently enhance immunostimulations in healthy humans. Probiotics may influence the levels and activity of the human gut microbiota. Non-absorbable antibiotics are increasingly used to induce modifications in intestinal microbiota without substantially affecting bacteria in other districts of the human body, thus minimising the potential for spreading antibiotic resistence. Clearly more work needs to be carried out to reveal microbiota changes and the complex mechanisms through which these changes may contribute to the determinism of gastrointestinal diseases.