A 50-year-old man with peptic ulcer disease undergoes endoscopic biopsy. The CLO (Campylobacter-Like Organism) test turns pink/magenta within 30 minutes. Which enzyme of Helicobacter pylori is responsible for this colour change, and why does H. pylori produce it?
- A Catalase converting H₂O₂ to O₂ and water, generating gas bubbles
- B Oxidase reducing cytochrome c, which reacts with the test reagent
- C Urease splitting urea into ammonia and CO₂; ammonia raises pH, causing pH indicator in the test gel to turn pink ✓
- D Phospholipase A₂ cleaving mucosal phospholipids, releasing fatty acids that change test colour
Explanation
H. pylori produces large amounts of urease (encoded by ureA and ureB genes), which hydrolyses urea to ammonia (NH₃) and carbon dioxide. In the CLO test, the biopsy is placed in a gel containing urea and a pH-sensitive indicator (phenol red). Urease activity raises local pH due to NH₃ production, shifting the phenol red from yellow to pink/magenta. H. pylori's urease serves a survival function by locally neutralising gastric acid around the organism. It also contributes to mucosal damage (cytotoxic ammonia + stimulation of inflammatory cytokines). Catalase and oxidase positivity also characterise H. pylori but don't cause the CLO colour change.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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