In vivo characterization of selected complex IV B. bronchiseptica strains. A. Survival of wild-type female C57BL/6NCr (B6) mice inoculated with different strains of B. bronchiseptica. Groups of four mice were intranasally inoculated with 5 x 105 CFU of the indicated strains in 40 μl volumes as described in Methods. B. Female C57BL/6NCr (B6) mice were infected as above and sacrificed 3 days later. Lungs were removed, homogenized in sterile PBS, and aliquots were plated on selective media. The number of colony forming units (CFU) per lung is shown for each animal. C. Representative H&E-stained sections of lung tissue obtained on day 3 post infection with indicated strains (magnification, x5). D. Histopathological score of indicated strains based on criterion described in Methods. The * indicates P value of <0.0001 for RB50 vs. Bbr77 and RB50 vs. D445.