Salmonella Typhi evades killing after phagocytosis by macrophages using which specific intracellular survival strategy?
- A Escaping the phagosome into the cytoplasm using the type 3 secretion system (T3SS) encoded by SPI-1
- B Producing superoxide dismutase and catalase to neutralise reactive oxygen species
- C Preventing phagosome-lysosome fusion and surviving within a modified Salmonella-containing vacuole (SCV) using proteins encoded by SPI-2 ✓
- D Downregulating MHC class II on macrophages to avoid antigen presentation
Explanation
Salmonella Typhi survives and replicates within macrophages by residing in a modified membrane-bound compartment called the Salmonella-containing vacuole (SCV). Pathogenicity island 2 (SPI-2) encodes a second type 3 secretion system (T3SS-2) that injects effector proteins into the host cell to manipulate vesicular trafficking, preventing normal phagosome-lysosome fusion and acidification. The SCV acquires lysosomal markers but retains a neutral pH and avoids degradative enzymes. This intramacrophage survival is essential for systemic dissemination via bloodstream (bacteraemia) causing typhoid fever. SPI-1 T3SS mediates initial invasion of intestinal epithelial cells. Vi capsular antigen also contributes by inhibiting complement deposition and phagocytosis.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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