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A genus of gram-negative bacilli whose members are spiral shaped, showing corkscrewlike motility generated by multiple, usually polar flagella. Helicobacter species require low concentrations of oxygen for maximum growth and produce the enzymes oxidase, catalase, and urease.

Different species of Helicobacter are found in the stomachs of different animals: H. felis in cats and dogs, H. mustelae in the domestic ferret, H. nemestrinae in the pigtailed macaque, and H. acinonyx in captive cheetahs with gastritis. Helicobacter pylori, found in the human stomach, is extremely common. In the United States and similarly developed countries, its prevalence increases at about 1% per year of age so that the majority of adults above age 50 are infected. In less developed countries, infection rates are dramatically higher, with up to 80% of children infected.

Helicobacter pylori is present in virtually all cases of chronic gastritis, which progresses slowly (years or decades) from asymptomatic to atrophic gastritis with impaired acid secretion. Virtually all individuals with duodenal ulcers are infected with H. pylori, which colonizes sites in the duodenum. The termination of treatment for duodenal ulcers leads to a high rate of recurrence of the ulcers, but ulcer treatment plus eradication of H. pylori from the stomach usually leads to a permanent cure. A significant proportion of individuals with H. pylori-associated atrophic gastritis develop intestinal-cell metaplasia in the stomach, a condition which is known to represent a precancerous state.

Helicobacter pylori virulence factors include its shape and its ability to rapidly move into and through the gastric mucous coating, which protects the organism from stomach acid; its surface-associated urease enzyme which neutralizes stomach acid near the organism; a cytotoxin; and a fibrillar adhesin which binds the organism to the surface of gastric epithelial cells. Helicobacter pylori can survive in large numbers in spite of antibodies which are secreted into the stomach and the host immune cell response (inflammatory response) characteristic of gastritis.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
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