[Electron micrograph of H. pylori possessing multiple flagella (negative staining) by Yutaka Tsutsumi, M.D. Professor Department of Pathology, Fujita Health University School of Medicine, licensed under Copyrighted free use]
H. pylori has been associated with lymphomas of the mucosa-associated lymphoid tissue in the stomach, oesophagus, colon, rectum, or tissues around the eye, and of lymphoid tissue in the stomach. H. pylori infection usually has no symptoms but sometimes causes gastritis (stomach inflammation) or ulcers of the stomach or first part of the small intestine. The infection is also associated with the development of certain cancers occurring in less than 20% of cases. Many investigators have suggested that H. pylori causes or prevents a wide range of other diseases; however many of these relationships remain controversial.
Some studies suggest that H. pylori plays an important role in the natural stomach ecology, e.g. by influencing the type of bacteria that colonize the gastrointestinal tract. Other studies suggest that non-pathogenic strains of H. pylori may beneficially normalize stomach acid secretion, and regulate appetite. [From Wikipedia]