FIG 3.

Survival of mice after initial infection with Y. pestis CO92 mutants in a bubonic plague model and subsequent rechallenge to evoke pneumonic plague with WT CO92. Adult Swiss-Webster mice were challenged with the WT CO92 strain or one of the mutants (5 mice per group) by the s.c. route at infectious doses of 8 LD₅₀. Surviving mice from the initial challenge with the selected mutant groups were followed for 28 days p.i. and then rechallenged by the i.n. route with 10 LD₅₀ of WT CO92. Survival data were analyzed for significance by Kaplan-Meier survival estimates with the Bonferroni post hoc test. The P values are for comparison of the results for each of the strains to the results for WT CO92 or the naive control for the rechallenge study.