Fig. 1.

Mm infects and proliferates in S2 cells. (A) S2 cells were infected by MmGFP and visualized 24 and 72 h after infection. Phase-contrast images are shown on the left, and immunofluorescence is shown on the right. (B) Mm growth in S2 cells was enumerated by colony-forming units over a 4-day period. (C) MmGFP-infected S2 cells were stained with Lysotracker red. (Upper) Uptake of live bacilli. (Lower) Uptake of heat-killed bacilli. Fusion of phagosomes containing heat-killed Mm-containing with lysosomes is indicated by overlap of the entire bacterium with red fluorescence, demonstrating the low pH (5.5) of the phagosome. Examples of bacteria are indicated by arrows. (D) Infected S2 cells were fixed and stained with Alexa Fluor 594 phalloidin (red). Actin tails and clouds were found in proximity to intracellular bacteria.