Helicobacter

Abstract

In the new family Helicobacteraceae, the genus Helicobacter presently comprises more than 40 validly named species and four Candidatus species, a designation of provisional status adopted by the International Committee on Systematic Bacteriology for incompletely described procaryotes. Helicobacter species colonize the gastrointestinal and hepatobiliary tracts of humans and a variety of animal species. Helicobacters are nonspore-forming, gram-negative bacteria with curved, spiral, or fusiform cellular morphology that may vary with the age, growth conditions, and species identity of the cells. Strains of all species are motile, with a rapid corkscrew-like or slower wave-like motion due to flagellar activity. Most species have bundles of multiple sheathed flagella with a polar or bipolar distribution. Oxidase activity is present in all species, whereas most species also produce catalase. Many species, in particular gastric helicobacters, produce urease. The species of primary importance for human medicine is Helicobacter (H.) pylori. Other Helicobacter species are primarily pathogenic in animals; human infections may be classified as zoonoses with a variety of animals such as dogs, cats, pigs, birds, rabbits, hamsters and other rodents, horses, and nonhuman primates as potential sources of infection. However, these infections are of minor importance as compared with infection with H. pylori. Therefore, this chapter will focus on the human pathogen H. pylori.