Gut microbiota and its pathophysiology in disease paradigms

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.