FIG. 5.

Cytopathicity of L. pneumophila for U937 macrophages. Wild-type (solid squares) and NU269 (open squares) strains were used to infect U937 macrophages at an MOI of (A) 1 or (B) 10, and host cell viability was assessed at various times postinoculation Cytopathicity data are presented as the percentage of surviving macrophages in infected monolayers compared to the numbers in uninfected monolayers and represent the mean and standard deviation from six wells. Experiments were performed in triplicate with similar results. Significant differences were observed between the wild-type and mutant strains at 48 and 72 h postinoculation (Student's t test, P < 0.05).