FIG. 4.

Colonization by and dissemination of ΔpsaA, Δcaf1, and ΔpsaA Δcaf1 mutant strains of Y. pestis in BALB/cJ mice during bubonic plague. Mice were infected s.c. in the neck with ∼10² CFU of the wild-type (diamonds) or ΔpsaA (triangles), Δcaf1 (squares), or ΔpsaA Δcaf1 (circles) mutant strain. Mice were sacrificed at 36, 48, and 72 h postinfection, and colonization of the superficial cervical lymph nodes (A), spleen (B), and lungs (C) was determined. Each symbol represents an individual animal. Black bars correspond to the median number of CFU/g of tissue for each group in BALB/cJ mice. Red bars correspond to the median number of CFU/g of tissue for each group in C57BL/6J mice (from Fig. 1). The dashed line indicates the limit of detection. The symbol × indicates that a mouse was either euthanized or found dead at that time point. An asterisk in a graph indicates a significant difference in the median number of CFU/g of tissue between the ΔpsaA and Δcaf1 mutant-infected groups, whereas asterisks in the tables indicate significant differences in the median numbers of CFU/g of tissue compared to either the wild-type or the ΔpsaA Δcaf1 mutant strain (*, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.005; na, not applicable; ns, not significant). The data are a combination of three independent experiments. The numbers of tissue samples harvested for the wild-type and ΔpsaA, Δcaf1, and ΔpsaA Δcaf1 mutant strains, respectively, were 8, 8, 7, and 8 at 36 h; 11, 12, 16, and 16 at 48 h; and 11, 8, 15, and 15 at 72 h.