Figure 4. Legionella cells released from protozoa and macrophages.

A. castellanii (A), D. discoideum (B) and U937 human monocyte-derived macrophages (C) were infected at an MOI of 10 for 1 h with L. pneumophila strains Lp01 (WT), MF201 (tolC::kan), MF213 (tolC::kan/pML005-tolC), MF214 (tolC::kan/pML005) and lpl701 (dotA::kan). At different times post-infection, the bacteria released in the supernatants were diluted in the appropriate medium (see material and methods) and spread on BCYE agar plates for colony enumeration. The initial time points (t = 0) represent the number of extracellular bacteria after 1 hour of infection. The data are representative of two independent experiments performed in triplicate and error bars represent standard deviations.