At the turn of the 20th century, Elie Metchnichkoff, a Nobel Prize-winning Russian, made the revolutionary discovery of probiotics. Probiotics are “live microbial food supplements which beneficially affect the host animal by improving its intestinal microbial balance.” Lactic acid bacteria and bifidobacteria are the most common types of microbes used as probiotics, but certain yeasts and bacilli can also be helpful. They act by competitively inhibiting the pathogenic bacteria because they have greater adhesion to the tissues. They inhibit pathogens but do not inhibit friendly bacteria. Studies have shown that once the pathogenic organisms are replaced the reintroduction of the pathogen does not occur easily.