FIGURE 4.

Co-culture of various L. pneumophila Paris strains with U937 cells (A) and A. castellanii (B). Bacteria were used to infect host cells at a multiplicity of infection of 1 for 72 h. At various time points postinoculation, bacteria were quantified by plating aliquots on buffered charcoal-yeast extract agar plates to determine the CFU/ml. Results are means ± S.D. (error bars) of duplicate samples and are representative of at least three independent experiments. Statistically significant differences in the growth of Δlpp0931–33 strain compare with the wild type strain (determined by a Student's t test, p < 0.001) are indicated (***). Lpp, L. pneumophila Paris; Δ, isogenic mutant strains of Lpp; 0931–33, lpp0931–33; 0650, lpp0650; keto, lpp1788.