FIG 3.

Natural antibodies do not prevent dissemination of B. melitensis in the blood, whereas vaccine-induced specific antibodies reduce the bacteremia following a secondary infection. (A) Wild-type and MuMT^−/− C57BL/6 mice were immunized i.p. with 4 × 10⁴ CFU of B. melitensis (vaccinated group) or injected i.p. with PBS (naive group) and then treated with antibiotics for 3 weeks, as described in Materials and Methods. Sixty days after immunization, all mice were injected i.p. with 5 × 10⁷ CFU of mCherry-Br, and blood was collected at the indicated time points. The data represent the CFU per ml of blood and are representative of three independent experiments. The gray bars represent the medians. ***, P < 0.001; ns, not significant. (B) Wild-type C57BL/6 mice were infected with 4 × 10⁴ CFU of B. melitensis. Serum was collected at the indicated time points, and ELISA was performed to determine the isotype distribution of the Brucella-specific antibodies. The data represent the means ± SEM of results for 6 mice. O.D., optical density.