Nature and mode of action of probiotics in intestinal infections

Probiotics are increasingly gaining scientific and commercial interest as functional foods in this era of self-care and complementary medicine. They are usually defined as viable microorganisms that beneficially affect the host health when ingested. The microorganisms most frequently used as probiotic agents are lactobacilli, bifidobacteria, and yeasts, particularly Saccharomyces boulardii , usually designated as a biotherapeutic agent. The use of probiotics to ameliorate intestinal health has been proposed for many years and there is a relatively large volume of literature supporting their use in order to prevent or to treat intestinal disorders. Several modes of action by which probiotics may act when used in the prevention and therapy of intestinal infections have been hypothesised, including stimulation of specific and aspecific immunity, competition for nutrients, inhibition of epithelial and mucosal adherence, inhibition of bacterial toxins, and production of antimicrobial substances. In this review, the present knowledge on the mode of action of probiotics deriving from in vitro and in vivo studies is discussed.