Protective Efficacy and Safety of Live Anthrax Vaccines for Mice

The safety and protective efficacy of the Sterne vaccine strain of Bacillus anthracis and of a recombinant Bacillus subtilis strain were investigated in mice. Strains of mice which vary in their natural resistance to killing by the Sterne strain were used. Vaccination with Sterne spores protected Sterne-resistant CBAJ mice against challenge with a fully virulent strain of B. anthracis, but only at vaccine doses within a magnitude of the 50 lethal dose LD50. The Sterne-susceptible AJ mice were not protected. Bacillus subtilis recombinant strain PA2, which produces the protective antigen component of anthrax toxin, protected CBAJ but not AJ mice. Both strains of mice developed high antibody titers to protective antigen. BALBcJ and CBAJ mice were similarly resistant to lethal Sterne infection, - but BALBcJ mice were more difficult to protect by immunization with either live vaccine. The inbred mouse model for anthrax is recommended for testing the efficacy and safety of new vaccines and characterizing the mechanisms of immunity to anthrax.