FIG 9.
Survival analysis of mice infected with WT Y. pestis CO92 and its complemented mutant strains by the route causing pneumonic plague. Mice (10 per group) were challenged by the i.n. route with 5 × 105 CFU (representing 1,000 LD50s of WT CO92) of WT Y. pestis CO92, its various mutants, and the complemented Δpla single mutant or the Δlpp Δpla double mutant (at day 0) and observed for mortality. The data were analyzed by using Kaplan-Meier survival estimates, and a P value of ≤0.05 was considered significant. The data between WT CO92 and its various mutants as well as between the Δpla single mutant and the Δlpp Δpla double mutant were compared.