Figure 5. Intracellular lifestyles of bacterial pathogens and barriers in the treatment of intracellular infections.

(A) Intracellular bacteria penetrate mammalian cells by endocytosis, phagocytosis or pinocytosis (1), and reside inside different subcellular compartments: the endosome (2), the endolysosome (3; formed by fusion of the endosome with a lysosome) or the cytosol (5), after escaping endosome inclusion (4, light‐blue dotted ring) (Cossart & Sansonetti, 2004; Ray et al, 2009). (B) Free phages must cross the eukaryotic cell membrane by non‐specific (a) or receptor‐mediated (b) entry. Endocytosed phages may then escape the vacuole (c, light‐blue dotted ring) or remain in the endosome (blue ring) with eventual fusion to a lysosome (d). After cytosolic release (c) or lysosomal fusion (d), viable phages may be released from the mammalian cell via exocytosis (e). * indicates bacteria that can replicate in more than one host cell compartment. The exact details of how phages reach their intracellular targets are still largely unknown (?).