FIG. 1.

The L. pneumophila mutants are defective in killing and exiting U937 macrophages, but not in intracellular replication. (A) Cytopathogenicity to infected cells (MOI of 5) was determined by Alamar blue assays and compared to that of the noninfected cells. (B) Growth kinetics within U937 macrophages. The indicated numbers of bacteria represent the combined numbers of intracellular bacteria and bacteria released into the supernatant. (C) Bacteria released into the tissue culture medium. (D) Intracellular bacteria. Values are the means of triplicate samples, and error bars represent standard deviations.