FIG. 2.

Homologous efficacy of B. abortus and B. melitensis vaccine strains. Groups of three to seven female BALB/c mice were vaccinated with 1 × 10⁶ CFU unmarked B. abortus vaccine strain, S19, or PBS. Groups were allowed to rest for either 12 weeks (A and D), 16 weeks (B and E), or 20 weeks (C and F) postvaccination. At these time points, mice were subsequently challenged with 1 × 10⁴ CFU 2308 (A to C) or 16M (D to F) and allowed to rest 1 week. After 1 week, mice were euthanized via CO₂ asphyxiation and spleens were collected. Data are reported as the log₁₀ recovery of Brucella from spleens, with individual mice in each treatment group represented. The solid line at 0.69 logs represents the lower limit of detection, which is ≥5 CFU. *, P < 0.05 compared to naïve animals by ANOVA; #, P < 0.05 compared to accepted vaccine strain (S19 or Rev 1) by ANOVA.