A genus of helical, curved, or straight microaerophilic bacteria with rounded ends and multiple sheathed flagella (unipolar or bipolar and lateral) with terminal bulbs; form nonpigmented, translucent colonies, 1–2 mm in diameter; catalase and oxidase positive. Found in gastric mucosa of primates, including human beings and ferrets; some species are associated with gastric and peptic ulcers and predispose to gastric carcinoma. The type species is H. pylori.