Intracellular growth of the wild-type, dotO mutant and flaA mutant L. pneumophila strains in epithelial cells. (A) A549 and NCI-H292 cells were infected with L. pneumophila AA100jm strain (MOI of 100). (B) A549 cells were infected with AA100jm and dotO mutant (MOI of 100). (C) A549 cells were infected with Corby and flaA mutant (MOI of 100). The number of bacteria at 0 h point is set as 1 and that at the indicated points is presented as the relative log10 CFU in cultures. Each data point represents the mean ± SD of triplicate cell cultures. *, P < 0.05; **, P < 0.01 (compared to cells infected with the wild-type strains).