FIG. 3.

Recovery of RetS mutant derivatives in a mouse model of acute pneumonia. Lightly anesthetized 8- to 10-week-old female C57BL/6 mice were infected with approximately 5 × 10⁵ CFU of each bacterial strain. The mice were euthanized 18 h postinfection, and the lungs were removed, homogenized, and resuspended in Hanks' balanced salt solution plus 0.25% Triton X. Serial dilutions of organ suspensions were plated on Vogel-Bonner minimal medium to determine CFU/gram of tissue. Results are expressed as the ratio of CFU recovered/gram of tissue (output) to CFU present in the initial inoculum (input) and represent results from n = 10 to 15 mice per strain; the line shows the geometric mean for each group. The Mann-Whitney test was used to calculate P values (two-tailed) for each pairwise comparison. *, P < 0.0001 compared to the ΔretS attB::retS strain; **, P ≤ 0.003 compared to the ΔretS strain; ***, P = 0.0021 compared to the ΔretS strain and P = 0.0232 compared to the ΔretS attB::retS strain. The wild-type and mutant alleles of retS are expressed as single-copy chromosomal integrates under the control of the native retS promoter in a ΔretS strain.