These remarkable organisms survive the extreme acidity of the stomach because of their powerful urease. This enzyme creates an alkaline microenvironment by hydrolyzing urea to ammonia. Urea is a waste product of protein catabolism by the body's cells and is normally present in the gastric juices.

Once the bacteria reach the mucus that coats the stomach or duodenal lining, they use their flagella to corkscrew through the mucus to the epithelial cells. In this location the pH of the mucus is nearly neutral, and the bacteria attach to the mucus-secreting epithelium or multiply adjacent to it. Bacterial products incite an inflammatory response in the wall of the stomach, and mucus production decreases. Once infection occurs it persists for years, often for life. From 10% to 20% of infected persons develop ulcers; 65% to 80% of patients with gastric ulcers and 95% of those with duodenal ulcers are infected with H. pylori. The thinning of the protective mucus layer at the site of infection (figure 24.8) probably accounts for the development of

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