The Vi antigen of Salmonella paratyphi B

Salmonella paratyphi B possesses a Vi antigen essentially similar to the Vi antigens of Salm. typhi and Salm. paratyphi A. 2. The biological function of the Vi antigen of Salm. paratyphi B is to protect the O antigen against the action of the natural or immune O antibody, thereby increasing the virulence of the microorganism. 3. The most suitable paratyphoid-B vaccine strains are those that develop both the Vi and the O antigens in maximum quantities. The methods of testing vaccine strains of Salm. paratyphi B are essentially the same as those applied to the virulent Vi+O form of Salm. typhi. 4. Evidence is brought to show that Kauffmann's conclusion that Salm. paratyphi B does not develop Vi antigen is unfounded. The so-called O-factors V and V obviously cannot be classified as O antigens. 5. It is suggested that the symbol V of the Kauffmann-White schema be abandoned and this antigenic component be classed as the Vi antigen of Salm. paratyphi B.