Effect of lactic acid bacteria on diarrheal diseases

Microbial balance is an important factor in the maintenance of intestinal homeostasis, and yogurt or fermented milk supplementation has been proposed to control diarrheal diseases. A number of studies using animal models and clinical studies in humans have confirmed the beneficial effect of such fermented products in case of lactose intolerance, viral diarrhea or antibiotics-associated diarrhea. The mechanisms by which lactic acid bacteria exert their effects are multiple. Bacterial lactase improves the absorption of lactose, but fermented products slow down the intestinal transit facilitating the action of residual intestinal lactase. The transient passage of lactic acid bacteria in the digestive tract may represent a microbial barrier against the development of pathogenic bacteria, probably due to the release of compounds contributing to the maintenance of colonization resistance to pathogens. The beneficial effects are mainly described in the presence of live bacteria, but inactivated bacteria may also present preventive or curative capacities in diarrheal diseases. Moreover, lactic acid bacteria has been described as reinforcing the non-specific immune defence but also specific immunity, particularly the secretory immune system mediated by secretory IgA or IgM in response to particulate infectious antigens and perhaps to soluble food antigens. Other possible mechanisms include the trophic effect on the intestinal layer, and a down-regulatory activity in cow's milk allergy as well as anti-inflammatory effects have also been suggested.