Probiotics can enhance the host defense system against pathogens. The mucosal epithelial cell barrier is the first line of defense against pathogen attack that may be enhanced by the promotion of mucin production or reduction of gut permeability. Promoting mucin production and reducing intestinal permeability may prevent penetration of pathogenic organisms and toxic substances. Factors from probiotic microorganisms can increase mucin production in cell culture [6], prevent enteropathogen-induced epithelial cell injury [7], and reduce intestinal permeability in mice [8]. Certain proteins are important for probiotic adhesion to host cell surfaces and can obstruct pathogen adhesion to the same surface. For example, surface-layer (S-layer) proteins present on the surfaces of L. crispatus and L. helveticus were able to prevent
adhesion of the foodborne pathogen, Escherichia coli O157:H7 to Hela, HEp-2 and T84 cells