Vaccination against anthrax with attenuated recombinant strains of Bacillus anthracis that produce protective antigen

The protective efficacy of several live, recombinant anthrax vaccines given in a single-dose regimen was assessed with Hartley guinea pigs, These live vaccines were created by transforming Delta ANR and Delta Sterne, two none ncapsulated, nontoxinogenic strains of Bacillus anthracis, with four differ ent recombinant plasmids that express the anthrax protective antigen (PA) p rotein to various degrees. This enabled us to assess the effect of the chro mosomal background of the strain, as well as the amount of PA produced, on protective efficacy. There were no significant strain-related effects on PA production in vitro, plasmid stability in vivo, survival of the immunizing strain in the host, or protective efficacy of the immunizing infection. Th e protective efficacy of the live, recombinant anthrax vaccine strains corr elated with the anti-PA antibody titers they elicited in vivo and the level of PA they produced in vitro.