 Intestinal barrier is a functional barrier that separates the gut lumen from the inner host. It consists of mechanical elements mucus, epithelial layer, humoral elements defensins, IgA, immunologic elements lymphocytes, innate immune cells, muscular and neurological element. Although the normal intestinal microbiota is the main source of endogenous pathogens, it also contributes to the functional integrity of the intestinal barrier through its interaction with the other components of the barrier. Failure of any of these components will result in a breakdown of the protective intestinal barrier with the consequence of recurrent intestinal-derived bacteremiasepticemia. A breakdown of the normal microbiome has been implicated in the development of various pathologic states, including Clostridium difficile infection, inflammatory bowel disease, intestinal graft-versus-host disease following allogeneic hematopoietic progenitor cell transplant, colon cancer, and metabolic disorders such as obesity and non-alcoholic steatohepatitis. 