Salmonellosis in mice: studies on oral immunization with live avirulent vaccines.

The avirulent Salmonella typhimurium galE strain G30, following oral feeding to mice, developed a state of immunity to a secondary oral challenge with virulent Salmonella typhimurium. This immunity was concommitant with the development of intestinal and serum antibodies and delayed-type hyepersensitivity (DTH) to Salmonella antigens. In contrast, repeated oral doses of a hybrid E. coli vaccine, which expresses the O antigens of Salmonella typhimurium, provided a lesser degree of immunity and, although able to stimulate the formation of serum antibodies, it elicited only a low level of intestinal antibodies and no measurable DTH.