In cell biology, a phagosome is a vesicle formed around a particle absorbed by phagocytosis. The vacuole is formed by the fusion of the cell membrane around the particle. A phagosome is a cellular compartment in which pathogenic microorganisms can be killed and digested. Phagosomes fuse with lysosomes in their maturation process, forming phagolysosomes.
Some bacterial pathogens that enter cells inside phagosomes either reproduce inside of the formed phagolysosome (Coxiella spp.) or escape into the cytoplasm before the phagosome fuses with the lysosome (Rickettsia spp.). Many mycobacteria, including Mycobacterium tuberculosis   and Mycobacteria avium paratuberculosis , manipulate the host macrophage to prevent nitrous acid-containing lysosomes from fusing with phagosomes and creating mature phagolysosomes. Such incomplete maturation of the phagosome maintains an environment favorable to the pathogens inside it. 
- Hackstadt T and Williams J C "Biochemical stratagem for obligate parasitism of eukaryotic cells by Coxiella burnetii." Proc Natl Acad Sci U S A 1981 May; 78(5) 3240–3244.
- Winkler H H "Rickettsia Species (As Organisms)" Annual Review of Microbiology Vol. 44: 131-153
- MacMicking, JD; Taylor, GA; McKinney, JD (2003). "Immune control of tuberculosis by IFN-γ –inducible LRG-47". Science 302 (5645): 654–659. doi:10.1126/science.1088063. PMID 14576437.
- Vandal, OH; Pierini, LM; Schnappinger, D; Nathan, CF; Ehrt, S (August 2008). "A membrane protein preserves intrabacterial pH in intraphagosomal Mycobacterium tuberculosis". Nat Med. 14 (8): 849–854. doi:10.1038/nm.1795. PMC 2538620. PMID 18641659.
- Kuehnel, MP; Goethe R; Habermann A; Mueller E; Rohde M; Griffiths G; Valentin-Weigand P. (August 2001). "Characterization of the intracellular survival of Mycobacterium avium ssp. paratuberculosis: phagosomal pH and fusogenicity in J774 macrophages compared with other mycobacteria". Cell Microbiol. 3 (8): 551–566. doi:10.1046/j.1462-5822.2001.00139.x. PMID 11488816.
- Tessema, MZ; Koets AP; Rutten VP; Gruys E. (November 2001). "How does Mycobacterium avium subsp. paratuberculosis resist intracellular degradation?". Vet Q. 23 (4): 153–162. doi:10.1080/01652176.2001.9695105. PMID 11765232.