Salmonella typhosa Vi antigen and its immunizing potential.

Abstract

A series of cultures of typhoid bacilli containing Vi antigen were much more virulent for mice than strains in which the Vi antigen was not present. Vaccines prepared from all the Vi strains tested produced a much higher level of active immunity than vaccines prepared from W types lacking the Vi antigen. Sera of rabbits immunized with vaccines made from Vi strains produced a much higher level of passive immunity in mice than sera of rabbits immunized with non-Vi strains. The Vi antigen contained in vaccines prepared from certain strains and, one in particular, proved to have a greater thermostability and greater general stability, as tested by storage, than the Vi antigen of other strains. An acid extract of a Vi strain produced a high level active immunity in mice.