Composition and immunochemical properties of the cell surface proteins of Vibrio cholerae

The composition and immunochemical properties of cell surface proteins of Vibrio cholerae belonging to both the biotypes (classical and El Tor) and the serotypes (Ogawa and Inaba) were investigated. Proteins were isolated by extraction with EDTA/NaCl. When the extract was further treated with sodium deoxycholate, a product significantly enriched with the major protein was obtained. The surface localization of these proteins was confirmed by immunoelectron microscopy using protein A-colloidal gold particles as probes. Antisera to these proteins possessed complement-mediated bactericidal activities towards V. cholerae strains belonging to both the biotypes and the serotypes, and upon crossed immunoelectrophoresis produced several immunoprecipitation reactions towards whole-cell sonicates belonging to all types of V. cholerae. These proteins were immunogenic in the rabbit intestine, as antibodies of two classes (IgG and IgA) were detected in the intestinal fluids. The intestinal immune response was greatly enhanced when cell surface proteins were administered with liposomes. These results suggest that cell surface proteins represent common antigens of V. cholerae and can be explored as vaccine candidates against cholera.