Figure 4.

The outcome of tularemia vaccination trials can be influenced by differential growth. Survival of BALB/c mice vaccinated three times with PBS (squares) or live Ft LVS (triangles) prior to challenge with Ft S4. In (A) all Ft were grown in MHB (open symbols); in (B), all Ft were grown in BHI (closed symbols). Asterisks indicate significant differences between PBS- and LVS-immunized groups that were identically-challenged. Actual challenge doses were 25 CFU of MHB-Ft S4 (A) and 34 CFU BHI-Ft S4 (B). Actual p < 0.0001 (A) and p = 0.0001 (B). Median survival times (MTS) for LVS-immunized mice were ≥ 14 d (A) and 12.5 d (B); for PBS-immunized mice the corresponding values were 6.5 d (A) and 5 d (B). The survival data from 30 mice used in two independent experiments with 6–8 mice/group are represented as Kaplan–Meier survival curves with statistical analysis by the Log-rank (Mantel–Cox) test.