Name a common intracellular pathogen that survives inside macrophages by inhibiting phagosome-lysosome fusion.

Name a common intracellular pathogen that survives inside macrophages by inhibiting phagosome-lysosome fusion.

• A. Staphylococcus aureus
• B. Mycobacterium tuberculosis
• C. Streptococcus pneumoniae
• D. Escherichia coli

Answer: (B)

Inside macrophages, pathogens are engulfed into phagosomes that typically mature and fuse with lysosomes to form phagolysosomes, where they are killed by acidic pH and degradative enzymes. The ability to block this maturation step lets some intracellular bacteria survive and replicate within the host cell. A well-known example is Mycobacterium tuberculosis, which prevents phagosome-lysosome fusion and resists the hostile environment inside the phagosome. This strategy enables the bacilli to persist, often in a latent form, and drives the granulomatous lesions characteristic of tuberculosis. The other organisms listed do not primarily rely on blocking phagosome-lysosome fusion as a central survival tactic. Staphylococcus aureus and Streptococcus pneumoniae can be phagocytosed and killed in the phagolysosome, with survival depending more on other virulence factors and evasion strategies. Escherichia coli is typically extracellular or cleared after phagocytosis rather than establishing persistent intracellular residence by preventing phagosome maturation.

Inside macrophages, pathogens are engulfed into phagosomes that typically mature and fuse with lysosomes to form phagolysosomes, where they are killed by acidic pH and degradative enzymes. The ability to block this maturation step lets some intracellular bacteria survive and replicate within the host cell. A well-known example is Mycobacterium tuberculosis, which prevents phagosome-lysosome fusion and resists the hostile environment inside the phagosome. This strategy enables the bacilli to persist, often in a latent form, and drives the granulomatous lesions characteristic of tuberculosis.

The other organisms listed do not primarily rely on blocking phagosome-lysosome fusion as a central survival tactic. Staphylococcus aureus and Streptococcus pneumoniae can be phagocytosed and killed in the phagolysosome, with survival depending more on other virulence factors and evasion strategies. Escherichia coli is typically extracellular or cleared after phagocytosis rather than establishing persistent intracellular residence by preventing phagosome maturation.