FIG. 3.

Deletion of ompX attenuates virulence of Y. pestis CO92 in rat pneumonic infection. Groups of Sprague-Dawley rats (n = 3/group/challenge) were challenged intranasally with 10-fold serial dilutions of the WT Y. pestis CO92 (10² to 10⁴ CFU) or the isogenic ΔompX derivative (10² to 10⁸ CFU). The animals were monitored for morbidity and mortality through 10 days postchallenge. The graph shows survival of the animals challenged with the WT or ΔompX strains. Survival comparisons between the animals infected with the highest number of WT organisms that killed 100% of the animals (10⁴ CFU) and the animals infected with that number of ΔompX organisms were evaluated by the log rank test (P = 0.01). Data represent combined survival numbers from three experiments.