are commonly isolated from the oral cavity,especially dental plaque and the tongue,although they usually comprise less than 1% of the total cultivable microflora . However ,their proportios and prevalenceincrease in advanced carieslesion both of the enamel and of the root surface. A number of homo- and hetero-fermentative speces have been identified,producing either lactate or lactate and acetate, respectively, from glucoes. The most common species are sssss