FIG. 2.

Invasion and intracellular growth of L. pneumophila strains in A. castellanii at 37°C. After growth to post-exponential phase in BYEα-MOPS, wild-type L. pneumophila (WT), the salt-resistant mutant (Salt^R), and STM-1, -2, and -3 (A) and STM-4, -5, and -6 (B) were incubated for 2 h with A. castellanii. The initial time point (T = 0 h) is the log CFU milliliter⁻¹ of input bacteria. The arrow at T = 4 h, after 2 h of gentamicin killing of extracellular bacteria, represents invasion. Subsequent time points represent intracellular replication. Error bars, standard deviations.