Figure 1.

Role of Y. pestis CO92 genes identified through the signature-tagged mutagenesis screen in virulence using bubonic and pneumonic plague mouse models. Survival analysis of female Swiss-Webster mice infected with WT CO92 or one of the indicated mutant strains (n = 10) in a bubonic plague model at the dosage equivalent to 18 LD₅₀ of WT Y. pestis CO92 (A) or in a pneumonic model at the dosage equivalent to 11 LD₅₀ of WT Y. pestis CO92 (B). Animals were monitored for up to 25 days p.i. (C) Survived mice (n = 5–9) following the initial i.n. mutant infections (B) and a group of naïve control mice (n = 5) were subsequently challenged with 10 LD₅₀ WT CO92 and observed for morbidity/mortality for 14 days p.i. (35 days total from initial infection). The data were analyzed for significance by using Kaplan–Meier survival estimates. The P-values were determined based on comparison of animal survival for each mutant to the survival of WT CO92-infected control animals or the groups indicated by a line. Two independent experiments were performed and the data from the second set constituting a group size of 10 animals/group were presented.