Research in Plague Immunity

The ultrastructure of the plague bacillus and its relationship to immunity were studied by electron transmission and scanning electron micrsocopic methods. In electron micrographs of colonies, the extracellular material is clearly present after 24 h ofgrowth in virulent strain cultures but not in avirulent strain EV76 Paris R. The material did appear in EV76 Paris R, however, after 48 h of culture, as well as in once-passaged EV 406. With the addition of Ca2 and Mg2 to the medium virulent Y. Pestis, grown at 37 C, acquired more Antigenic components. Experiments on highly susceptible nonhuman primates C. aethiops with avirulent strain EV76 Paris F given orally demonstrated 1 that the vaccine strain is nonlethal 2 that the vaccine prevents both bubonic and pneumonic infections by challenge with a fully virulent strain of Y. pestis.