Which organism is the primary etiologic agent of peptic ulcers?

• A. Escherichia coli
• B. Helicobacter pylori
• C. Shigella dysenteriae
• D. Bordetella pertussis

Answer: (B)

Peptic ulcers arise when the stomach’s or duodenum’s protective mucus is overwhelmed by acid and inflammatory damage. The organism that best explains most of these ulcers is Helicobacter pylori, a curved gram-negative bacterium that can live in the stomach’s harsh, acidic environment by producing urease. Urease breaks down urea into ammonia and carbon dioxide, locally raising the pH and allowing the bacteria to persist in the mucus layer that protects the mucosa. This persistent colonization triggers chronic gastritis and inflammatory injury to the stomach lining, gradually weakening the mucosal barrier and creating ulcers in the stomach or first part of the small intestine.

Other bacteria listed don’t fit as primary causes of peptic ulcers. Escherichia coli is a common gut inhabitant not typically linked to gastric ulcers; Shigella dysenteriae causes severe colitis with dysentery rather than peptic ulcers; Bordetella pertussis is a respiratory pathogen with no role in stomach ulcers. Recognizing H. pylori as the main culprit explains why therapy focuses on eradicating the infection alongside acid suppression.