FIG. 6.

Intracellular growth of L. pneumophila in iron-depleted U937 cells. The numbers of wild-type (solid bars) and NU269 (open bars) cells were determined in U937 cell monolayers cultured in medium containing 0, 25, or 50 μM DIP. Data represent means and standard deviations recovered from triplicate wells. The experiment was performed in triplicate with similar results. Significant differences were observed between the wild-type and mutant strains at 25 and 50 μM DIP (Student's t test, P < 0.05).