FIG. 2.

icmF and dotU mutants are defective for formation of replicative vacuoles. Bone marrow-derived macrophages were infected at an MOI of 1.0 for 1 h, after which they were washed and either fixed or incubated for an additional 13.5 h and then fixed. L. pneumophila were stained with antibody as described in the text (see Materials and Methods). The number of bacteria within each macrophage was assessed microscopically at each time point and assigned to one of the following four categories: 1 to 2 bacteria per macrophage, 3 to 6 bacteria per macrophage, 7 to 12 bacteria per macrophage, or more than 12 bacteria per macrophage. Approximately 100 infected macrophages were counted per coverslip (except for the dotA strain Lp03, for which 50 macrophages per coverslip were examined), and three coverslips were analyzed for each strain at each time point. Means and standard deviations are shown.