Cholera is exclusively a disease of man caused by the gram negative bacterium Vibrio cholerae. The pathogenic process requires both colonization of the small bowel by the bacterium and production of at least one toxin, cholera toxin. Immunity involves both antibacterial and anti-cholera toxin responses. V. cholerae is motile by virtue of a single polar flagellum. In the first three year grant period we isolated motility and flagellar structural mutants of V. cholerae to distinguish the role of motility from that of the flagellar structure in colonization. Some of these mutants were evaluated in 3 different animal models. The results clearly show that motility is required for full virulence. While we did not observe, using these animal models, a major role of the flagellar structure in colonization it is still possible that it plays a minor role. Additionally, the flagellar structure may play a role in protective immunity. Since we did not observe a major role for the flagellar structure in colonization, in the continuation grant of this project we propose to examine and identify specific bacterial and flagellar components which elicit an immune response in humans. These immunogens will be evaluated for their location on the bacterium, whether they are exclusive to the flagellar sheath, and if they are involved in adherence and protective immunity using genetic, biochemical, and immunological methods. An in vitro adherence assay we recently developed using human small bowel tissue will be used to evaluate these immunogens. While animal models using rabbits and infant mice are available to assess V. cholerae pathogenesis, colonization and adherence, they are complex, expensive, involving whole animals, surgery and are very limited in their applicability to molecular studies of specific adherence factors. These experiments will identify specific bacterial components which may be likely candidates for inclusion in or components of a vaccine.
