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 degrees 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.