Engineered commensal bacteria as delivery systems of anti-infective mucosal protectants

The mucosal surfaces of the gastrointestinal, genitourinary, oral and respiratory systems represent the principal portals of entry for most pathogenic microorganisms, as well as the first line of defence against the majority of infections. Mucus-associated lymphoid tissue represents a critical component of the mammalian immune system, and mucosal exposure to infectious agents and other foreign antigens is responsible for the production of antigen-specific secretory IgA and, frequently, serum antibodies, as well as for local cell-mediated immune responses (Conley and Delacroix, l 987; Ogra et al., 1999). Based on these observations, mucosa! surfaces have been seen as obvious sites for delivering protective agents against infectious diseases, mainly those mucosally acquired, thus preventing widespread colonization during the early stages of infection.