In the context of Legionella infection, what protects the phagosome containing Legionella bacteria from fusion with lysosomes in host cells?

• A. A specialized membrane derived from the endoplasmic reticulum
• B. A capsule composed of polysaccharides
• C. A thick peptidoglycan layer produced by the bacteria
• D. An acidic environment created by the host cell

Answer: (A)

Verified step by step guidance

1. Understand the process of phagocytosis: Normally, when a macrophage engulfs bacteria, the bacteria are enclosed in a phagosome, which then fuses with lysosomes to form a phagolysosome where the bacteria are destroyed.
2. Recognize that Legionella pneumophila has evolved mechanisms to avoid destruction by preventing the fusion of the phagosome with lysosomes.
3. Identify that Legionella modifies the phagosome membrane by recruiting vesicles derived from the host cell's endoplasmic reticulum (ER), creating a specialized membrane around the phagosome.
4. This ER-derived membrane prevents the normal maturation of the phagosome and its fusion with lysosomes, allowing Legionella to survive and replicate within the host cell.
5. Conclude that the protection of the phagosome from lysosomal fusion is due to this specialized ER-derived membrane, rather than bacterial capsules, peptidoglycan layers, or acidic environments.