Gastric organisms were first observed more than 100 years ago and their association with gastritis has been recognized since the 1970s . The true implication of these microbes was not fully realized, however, until 1982 when Marshall and Warren identified and subsequently cultured the gastric bacterium, Campylobacter pyloridis, later reclassified as Helicobacter pylori (H. pylori) . This organism is now known to cause chronic gastritis, most peptic ulcers, and gastric adenocarcinoma and lymphoma. (See appropriate topic reviews.)
The bacteriology and epidemiology of H. pylori will be reviewed here. Understanding its bacteriology and the unique features that enable it to survive in an environment as hostile as the stomach are important in appreciating how H. pylori causes tissue injury and clinical disease. (See "Pathophysiology of and immune response to Helicobacter pylori infection".) The epidemiology of this infection sheds light on the geographic, ethnic, and racial differences in prevalence of H. pylori-associated diseases and the changing incidence of these conditions throughout the world.
Microbiology — H. pylori is a spiral shaped, microaerophilic, gram negative bacterium measuring approximately 3.5 microns in length and 0.5 microns in width (picture 1). In vitro, it is a slow growing organism that can be cultured on blood agar or selective media such as Skirrow's media incubated at 37ºC in a 5 percent oxygen atmosphere for three to seven days . Small, uniformly sized, translucent bacterial colonies form and the organisms can be morphologically characterized by Gram stain and their typical spiral or rod shaped appearance. High power microscopy reveals that the organism has two to seven unipolar sheathed flagella which enhance its mobility through viscous solutions.
If the growth environment is less than ideal, coccoid forms of H. pylori can occasionally be seen in culture . These coccoid forms are thought to represent an adaptation to hostile surroundings; they appear to be more resistant and may enable the organism to survive for periods of time outside the human host in feces or in drinking water.
In addition to morphologic characterization, the organism can be biochemically characterized as catalase, oxidase, and urease positive. Urease appears to be vital for its survival and colonization; it is produced in abundance, making up more than 5 percent of the organism's total protein weight. Bacterial urease activity is clinically important because it forms the basis for several invasive and noninvasive tests to diagnose infection (see "Indications and diagnostic tests for Helicobacter pylori infection").