FIG 1.

Passive transfer of immune serum provides protective immunity against challenge with a lethal dose of wild-type B. mallei. Groups of naive female BALB/c mice were vaccinated with B. mallei batA LAS (41) and exsanguinated 30 to 45 days postvaccination, and serum samples from these animals were pooled. Naive female BALB/c mice (7 weeks of age; n = 9 per group) were then injected intraperitoneally with 1 ml of pooled immune sera and challenged 48 h later with 5 LD₅₀ of wild-type B. mallei ATCC 23344 bacteria via the aerosol route using a Microsprayer device (25); controls consisted of age- and weight-matched naive mice injected with 1 ml of naive serum. Some animals received only a single dose of serum prior to infection, while others also received additional doses on days 7 and 14 postchallenge. Infected animals were monitored daily for signs of illness and morbidity. (A) Kaplan-Meier survival curves. (B) Survival data during the acute (days 1 through 10 postchallenge) and chronic (days 11 through 45 postchallenge) phases of infection. (C to E) Tissues were collected from survivors, homogenized, diluted, and spread on agar plates to determine bacterial loads. Symbols represent the values for individual animals; horizontal bars show mean total CFU for each group. The values below the groups in panels C to E show the percentages of animals that cleared bacteria from tissues from the different groups. The asterisk indicates that one mouse cleared bacteria from all three tissues.