In a search for bacteria having putative probiotic activity, we screened a collection of food-isolated microorganisms for the ability to survive at low pH in the presence of bile salts and for the production of antimicrobial compounds active against a number of animal pathogens. Among these, we found a strain that we classified as a member of Lactobacillus fermentum sp., and we further investigated its features. This organism was able to adhere to human enterocyte-like (Caco-2) cells with high efficiency as compared to that of a well known indicator strain. Chromatographic analysis indicated that at least two small (less than 3 kDa) factors were involved in mediating the in vitro interaction of L. fermentum with Caco-2 cells. Adhesion activity could be abolished by mild treatment of the bacterial cells in buffer and rescued by incubating them with either the same buffer after its use in the treatment or with chromatographic fractions containing each of the two factors, which indicated that these factors were loosely associated with the cell wall and that each of them was sufficient to warrant the adhesiveness of L. fermentum to Caco-2 cells. These data are suggestive of a novel mechanism of bacterial adhesion to epithelial cells.