The gut flora carries out important functions for human health, although most of them are still unknown, and an alteration of any of them, due to a condition of dysbiosis, can lead to relevant pathological implications. Commensal bacteria in the gut are essential for the preservation of the integrity of the mucosal barrier function and an alteration in the anatomic functional integrity of this barrier has been implicated in the pathophysiologic process of different diseases. The gut microflora plays a role in modulating the intestinal immune system; in fact, it is essential for the maturation of gut-associated lymphatic tissue, the secretion of IgA and the production of antimicrobial peptides. The enteric flora represents a potent bioreactor which controls several metabolic functions, even if most of them are still unknown. The main metabolic functions are represented by the fermentation of indigestible food substances into simple sugars, absorbable nutrients, and short-chain fatty acids. Furthermore, the gut microbiota exerts important trophic and developmental functions on the intestinal mucosa. This overview focuses briefly on the physiological role of the gut microbiota in maintaining a healthy state and the potential role played by disturbances of both the function and composition of the gut microbiota in determining important pathological conditions, such as irritable bowel syndrome, inflammatory bowel disease, metabolic syndrome, obesity, and cancer.

Neish A: Microbes in gastrointestinal health and disease. Gastroenterology 2009;136:65–80.
Gaskins HR, Croix JA, Nakamura N, Nava GM: Impact of the intestinal microbiota on the development of mucosal defence. Clin Infect Dis 2008;46:S80–S86.
Sekirov I, Russel SL, Antunes CM, Finlay BB: Gut microbiota in health and disease. Physiol Rev 2010;90:859–904.
Vrieze A, Holleman F, Zoetebdal EG, de Vos WM, Hoekstra JBL, Nieuwdorp M: The environment within: how gut microbiota may influence metabolism and body composition. Diabetologia 2010;53:606–613.
O’Toole PW, Claesson MJ: Gut microbiota: changes throughout the lifespan from infancy to elderly. Int Dairy J 2010;20:281–291.
Chung H, Kasper DL: Microbiota-stimulated immune mechanisms to maintain gut homeostasis. Curr Opin Immunol 2010;22:455–460.
Fava F, Danese S: Intestinal microbiota in inflammatory bowel disease: friend of foe? World J Gastroenterol 2011;17:557–566.
Miele L, Valenza V, La Torre G, Montalto M, Cammarota G, Ricci R, Mascianà R, Forgione A, Gabrieli MR, Perotti G, Vecchio FM, Rapaccini G, Gasbarrini G, Day CP, Grieco A: Increased intestinal permeability and tight junction alterations in non-alcoholic fatty liver disease. Hepatology 2009;49:1877–1887.
Lee YK, Mazmanian SK: Has the microbiota played a critical role in the evolution of the adaptive immune system? Science 2010;330:1768–1773.
Collins SM, Denou E, Verdu EF, Bercik P: The putative role of the intestinal microbiota in the irritable bowel syndrome. Dig Liver Dis 2009;41:850–853.
Barbara G, Wang B, Stanghellini V, de Giorgio R, Cremon C, Di Nardo G, Trevisani M, Campi B, Geppetti P, Tonini M, Bunnett NW, Grundy D, Corinaldesi R: Mast cell-dependent excitation of visceral-nociceptive sensory neurons in irritable bowel syndrome. Gastroenterology 2007;132:26–37.
Strachan DP: Hay fever, hygiene and household size. BMJ 1969;299:1259–1260.
Penders J, Stobberingh EE, van den Brandt PA, Thijs C: The role of the intestinal microbiota in the development of atopic disorders. Allergy 2007;62:1223–1236.
Cani PD, Delzenne NM: The role of gut microbiota in energy metabolism and metabolic disease. Curr Pharm Des 2009;15:1546–1558.
Al-Lahham SH, Peppelenbosch MP, Roelofsen H, Vonk RJ, Venema K: Biological effects of propionic acid in humans; metabolism, potential applications and underlying mechanisms. Biochim Biophys Acta 2010;1801:1175–1183.
Guarner F, Malagelada JR: Gut flora in health and disease. Lancet 2003;361:512–519.
Ley RE, Turnbaugh PJ, Klein S, Gordon JI: Microbial ecology: human gut microbes associated with obesity. Nature 2006;444:1022–1023.
Kalliomaki M, Collado M, Salminen S, Isolauri E: Early differences in fecal microbiota composition in children may predict overweight. Am J Infect Control 2008;21:213–234.
Greer JB, O’Keefe SJ: Microbial induction of immunity, inflammation, and cancer. Front Physiol 2011;1:168.
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