Growth of F. tularensis pdpA mutant and control strains in mouse macrophages. Bone marrow-derived macrophages were infected, and samples were lysed every 24 h to determine the number of viable bacteria (CFU) on agar medium. Squares, growth of parent strain F. tularensis (U112); inverted triangles, control strain R4 with a random transposon insertion not affecting intracellular growth; triangles, mutant 304-2; diamonds, mutant 304-2 with complementing plasmid pVIC314; circles, mutant 304-2 with plasmid pVIC311, which should not complement the genetic defect. Representative data from one of three repetitions are shown.