Protection of mice against Vibrio vulnificus disease by vaccination with surface antigen preparations and anti-surface antigen antisera

Abstract

Vaccination of mice with either Formalin-killed cells or cell extracts of a virulent strain and a weakly virulent strain of Vibrio vulnificus or with rabbit antisera (AS) against the Formalin-killed cells and cell extracts protected against the virulent strain of V. vulnificus. However, the virulent strain vaccines and AS elicited a significantly stronger immune response than the weakly virulent strain vaccines and AS. Adsorption of the AS with either the homologous or heterologous Formalin-killed cells significantly reduced the ability of the AS to protect mice. The major protective antigen(s) in the cell extracts migrated in the void volume of Sephacryl S-400 superfine, was not effectively sedimented by centrifugation at 100,000 x g for 2 h, had an isoelectric point of 3.8 to 4.2, and was sensitive to boiling or autoclaving for 15 min, periodate oxidation, and exposure to pH 12 but was resistant to 56° C, trypsin, pronase, RNase, neuraminidase, and pH 4.5. Electron microscopy revealed that the virulent strain possessed a more dense ruthenium red-staining layer on its outer membrane and had a much smoother surface than the weakly virulent strain. Our results provide evidence that a major protective antigen and virulence factor of V. vulnificus is a heat-labile, acidic polysaccharide located on the bacterial surface.