FIG. 4.

Evaluation of the efficacy of vaccination against B. abortus aerosol challenge. Groups of four or five female 6- to 8-week-old BALB/c mice were vaccinated via i.p. injection of 1 × 10⁶ CFU/ml of unmarked deletion mutant BAΔasp24, BAvirB2, BAΔmanBA, or BMΔasp24 or PBS for naïve controls. Mice were subsequently challenged with an aerosol chamber dose of 5 × 10⁹ CFU/ml B. abortus 2308 at 20 weeks postvaccination (heterologous challenge for BMΔasp24). Four weeks after the virulent challenge, the mice were euthanized, and lungs (A), livers (B), and spleens (C) were extracted to measure the recovery of the challenge organisms. Data are expressed as the log₁₀ recovery of 2308 from the entire organ, and the results for individual mice in each treatment group are shown. The solid line at 0.7 log represents the lower limit of detection, which is ≥5 CFU. For comparisons with naïve control animals using ANOVA with Tukey's honestly significant difference posttest, one asterisk indicates that the P value is <0.05 and two asterisks indicates that the P value is <0.01.