Figure 1.

The intracellular life cycle of F. tularensis. Francisella is internalized into macrophages by large pseudopodia. Inside cells, bacteria transiently reside in a phagosomal compartment that partially matures into a late phagocytic compartment, acquiring membrane markers of early (EEA1) and late endosomes/lysosomes (LAMP-1 and -2). Typical transmission electron microscopy images of intracellular Francisella are shown. Once in the host cell cytoplasm, Francisella takes advantage of available nutrients to actively multiply. Bacteria can be released from dead cells (by apoptosis and/or pyroptosis) or can be directly transferred by trogocytosis to neighboring cells.