FIG. 3.

Intracellular infection of human macrophages with L. pneumophila strains. U937 cell monolayers (n = 3) were infected at an MOI of 1 with strain 130b (●) and NU260 (□). Asterisks indicate significant differences (P < 0.01; Student's t test) in numbers of recovered bacteria between 130b and NU260. Comparable results were obtained in triplicate experiments, and the data presented here are from one representative experiment. Error bars indicate standard deviations.