Figure 4. Protective immunity experiments in guinea pigs vaccinated by a single immunization with various doses of the SterneΔhtrA spores.

(a) A Schematic representation of the single-immunization experiments is shown. (b) The Kaplan-Meier survival profiles of guinea pigs immunized with the indicated doses of SterneΔhtrA spores is shown. The animals (at least 10 per group) were challenged 5 weeks post-immunization with 100 × LD₅₀ of fully virulent Vollum spores (pXO₁⁺; pXO₂⁺) by SC infection (10⁴ spores/animal, upper panel) or respiratory IN exposure (10⁶ spores/animal, lower panel). See Fig. 6 for the anti-PA, anti-bacterial antigens and neutralizing antibody titres measured in the pre-challenged blood samples. The experiments described in this and all subsequent figures employed the SterneΔhtrA IIBR-BA106 strain.