FIG. 3.

Differentiation between extracellular and intracellular F. tularensis by use of monoclonal antibodies. Viable intracellular F. tularensis LVS/GFP/AVS cells expressing GFP appear green, while extracellular F. tularensis cells appear red after treatment with labeled antibodies specific for F. tularensis. (A) Disintegrating A. castellanii trophozoite containing Francisella-filled vesicles (day 18). (B) Individual vesicle containing viable F. tularensis GFP/LVS/ASV (day 18). (C) A. castellanii cyst containing viable F. tularensis inside the cyst double wall (day 40).