Bacterial burdens in the Lungs. 6-8 week old female CD1 mice were infected IN with 2×104-1×105 CFU of CO92 or CO92ΔyopH respectively. Mice were sacrificed at 24 h and 48 h post-infection and the lungs were weighed, crushed, and plated for CFU/g tissue. There is a significant difference in bacterial colonization of the lungs between wild type CO92 and CO92ΔyopH at both 24 h (*** p = 0.0002) and 48 h (***p = 0.0002) post-infection. These data are representative of two independent experiments with at least 6 mice per group. *** p = 0.0002, Mann-Whitney U test, CO92 infected lungs vs. CO92ΔyopH infected lungs at 24 h or 48 h post-infection, bar represents mean value.