pylori: A bacterium that is known to cause stomach ulcers and ulcers in the first part of the small intestine, or duodenum.

Helicobacter is a genus of Gram-negative bacteria possessing a characteristic spiral shape. Some species have been found living in the lining of the upper gastrointestinal tract, as well as the liver of mammals and some birds. The most widely known species of this genus is H. pylori which is a human pathogen and is responsible for most cases of peptic ulcer, chronic gastritis, and stomach cancer.