Protective antigens from El Tor vibrios. 1. The preparation and properties of a purified protective antigen from an El Tor vibrio (Ogawa subtype).

A biochemically and immunologically homogeneous antigenic fraction having the properties of a lipopolysaccharide has been isolated from the culture supernatant of an El Tor vibrio (Ogawa subtype). This antigen was very specifically protective for mice challenged with Ogawa strains of either El Tor vibrios or Vibrio cholerae. Rabbit antisera prepared against the antigen were passively protective for mice and highly vibriocidal but had little agglutinating activity. However, the antigen was able specifically to absorb agglutinins, as well as mouse-protective and vibriocidal antibody from serum prepared against whole bacterial cells. The specific protective activity of this lipopolysaccharide was much greater than that of vaccines made from whole bacterial cells, and its toxicity in animals was about equivalent to that of whole cells. The relationship of activity to toxicity therefore represented an improvement over the vaccines that were studied.