Fig. 1.
Kinetics of infection with Y. pestis strain CO92 or CO92 pCD1-. Bacteria (1 × 104) were introduced intranasally into C57BL/6 mice, and cfu per organ in the lungs (A and C) and spleen (B and D) were determined every 12 h for 3 days (CO92, A and B) or every 24 h for 4 days (CO92 pCD1-, C and D). The limit of detection is indicated by a dashed line. Each point indicates cfu recovered from a single animal. Symbols below the limit of detection represent mice that survived but did not have detectable numbers of bacteria; “X” indicates mice that succumbed to the infection. A solid line indicates the median of cfu recovered.