What Causes Stomach Ulcers?

A peptic ulcer is a sore or hole in the lining of the stomach or duodenum (the first part of the small intestine) and contrary to popular belief, these painful lesions are not caused by stress, consuming alcohol or eating spicy food. They are caused by the bacterium Helicobacter pylori (say Hel-ick-o-back-ter pie-lor-ee).

Helicobacter Features and Taxonomy

• Gram-negative
• Microaerophilic (need a level of oxygen lower than that found in the atmosphere)
• Acidophilic (able to tolerate an acidic environment)
• Slightly helical (spiral-shaped) bacillus
• Taxonomic class Deltaproteobacteria.

How Do Helicobacter Cause Ulcers?

Helicobacter pylori has several special features, virulence factors, that permit it to survive, thrive and infect the human stomach. These factors include:

• multiple polar flagella that enable the bacteria to penetrate the thick, viscous coating of the stomach
• the ability to make proteins that inhibit production of stomach acids
• adhesins on their bacterial fimbriae help H. pylori anchor themselves to the epithelial cells lining the stomach
• the ability to produce enzymes that inhibit phagocytosis of the bacteria by cells of the human immune system

How Did Scientists Figure Out That Bacteria Cause Ulcers?

The idea that bacteria can cause peptic ulcers was, until very recently, a controversial one. In 1982, Australian gastroenterologists Robin Warren and Barry Marshall discovered that the majority of their patients' stomachs were colonized by H. pylori. After these patients were administered appropriate antibiotics, the bacteria and ulcers disappeared.

In order to establish a specific cause and effect relationship between H. pylori and ulcer disease, Dr. Marshall took Koch's Postulates to the extreme and actually drank a liquid culture of the bacteria. The good doctor subsequently developed peptic ulcers, eliminating any doubt that Helicobacter was the causative agent.

Peptic Ulcer Symptoms and Diagnosis

The most common ulcer symptom is gnawing or burning pain in the abdomen between the breastbone and the belly button. Sometimes ulcers bleed, and a severe case may result in anemia or blood in vomit or bowel movements.

Although a blood sample can show if a patient's immune system has generated antibodies to H. pylori, presence of antibodies cannot distinguish between a previous and a current infection. Confirmation of an active H. pylori infection requires a series of biochemical tests.

Treatment of H. pylori Infection

Only a physician can determine the appropriate course of treatment for an individual patient. Physicians usually treat peptic ulcer disease with a combination of antibiotics as well as medication to decrease stomach acid production while the lining of the stomach heals.

Incidence of H. pylori Infection

Many people have H. pylori in their stomach; 20% of the US population, increasing up to 80% in the elderly. However, most infected people do not develop ulcers. Why H. pylori does not cause ulcers in every infected person is unknown. It is likely that infection depends on specific traits of the infected person, the strain of H. pylori, and other factors that are yet to be discovered.

Microbiology Sources

For more information on microbiology, see the Virtual Microbiology Classroom, Todar's Online Textbook of Bacteriology or the following sources:

Bauman, R. (2007). Microbiology with Diseases by Taxonomy. Pearson Benjamin Cummings.

Tortora, G., Funke, B. and Case, C. (2010) Microbiology: An Introduction. Tenth Edition. Benjamin Cummings

*If you or a loved one are ill, please see a doctor, not a computer.