A doctor refers the patient to a gastroenterologist for a stomach acid test and an upper gastrointestinal endoscopy, which revealed that this patient is a heavy acid producer and has a gastric peptic ulcer. Which of the following is the most likely causative organism for this patient’s condition?

• A. Shigella
• B. Listeria
• C. Leptospira
• D. Salmonella
• E. Helicobacter