BALB/c mice were immunized as described in Figure 1. Bacterial burden studies were then conducted as described in Materials and Methods. Briefly, lung (A), liver (B), and spleen (C) were harvested at 1, 3, 7, and 14 days post-challenge and bacterial counts were carried out. Each point represents the average of three mice sacrificed per time point + SD. On day 7 iFt plus CTB-immunized mice had significantly lower bacterial burden in tissues than iFt-treated mice (p<0.001). On day 14, all mice immunized with PBS or CTB alone succumbed to the infection, as indicated by a cross (+) on the x-axis. The data is representative of two experiments.