[What is Helicobacter pylori?: associated diseases in human].

Helicobacter pylori (H. pylori) is a spiral gram-negative bacterium, characterized by positive urease, catalase and oxidase activity. The complete resolution of the full genome has elucidated the biological characteristics, the pathogenicity, and the bacterial evolution. The infection is acquired in childhood by oral-oral transmission in developed countries, probably an intra-familiar transmission. The infection has an association with chronic histological gastritis, peptic ulcer, gastric cancer and MALT lymphoma in the stomach. All patients with H. pylori infection have histological gastritis and most of them remain asymptomatic for life. Only a minority of the infected individuals occurs ulceration or gastric cancer. Cure of the infection prevents recurrence of peptic ulcer without persistent treatments against ulceration. Concerning gastric cancer, WHO concluded in 1994 that H. pylori is a definite carcinogen in humans on the basis of epidemiological studies. Evidences that the infection leads to the development of gastric cancer have been accumulated in animal models as well as in vitro experimental studies. Such clinical diversities are caused by variations of H. pylori pathogenicity, host susceptibility, environmental factors including foods and those interactions. At present, an eradication treatment of H. pylori, combined with a proton-pump inhibitor and two antibiotics (clarithromycin and amoxicillin) is restrictedly approved in the patients with gastric or duodenal ulcer by Japanese health care system.