FIG. 4.

Intracellular growth of L. pneumophila in U937 macrophages. (A) Wild-type 130b- (solid squares) and mutant NU269- (open squares) were used to infect U937 macrophages at an MOI of 1 and then, at various times postinoculation, the numbers of bacteria were assessed. Panel B shows complementation performed with NU269(pMR20) (vertical striped bars) or NU269(pMR21) (horizontal striped bars) containing plasmids encoding the entire feoB or feoAB genes, respectively. Complemented strains were compared to wild-type and mutant bacteria containing the empty vector pMMB207 (solid and open bars, respectively). Data represent the mean and standard deviation from triplicate samples. Experiments were performed in duplicate or triplicate with similar results. Significant differences were observed between the wild-type and mutant strains between 24 and 72 h postinoculation in panel A and between NU269(pMMB207) and NU269(pMR20) or NU269(pMR21) at 72 h postinoculation (Student's t test, P < 0.01).