Fig. 2.

Bacterial burdens in the spleens and livers of infected mice. (A and B) Levels of Y. pestis at 24 and 60 h in the spleens of young and middle-aged female B10.T(6R) mice challenged with 1 × 10³ CFU of Y. pestis KIM5. At both time points, there was a statistically significant difference in bacterial burdens in the spleen. (At 24 h, 5 mice per group were used; *, P < 0.05. At 60 h, 9 young and 10 middle-aged B10.T(6R) mice were used; ***, P < 0.001 [by the Mann-Whitney test]. Data were pooled from two independent experiments.) Dotted horizontal lines indicate the lower limit of detection. (C and D) Bacterial burdens in the livers of young and middle-aged female B10.T(6R) mice at 24 and 60 h postinfection. There was no significant difference in bacterial burdens in the liver at 24 h, but a significant difference was observed at 60 h. (At 24 h, there were 5 mice per group; NS, no significant difference. At 60 h, 9 young and 10 middle-aged B10.T(6R) mice were used; **, P < 0.005 [by the Mann-Whitney test]. Data were pooled from two independent experiments.)