Campylobacter (Greek campylo, curved; bacter, rod) are motile, non-spore-forming gram-negative rods. Today they are recognized as a very common cause of gastrointestinal (GI) infection in humans in many parts of the world. Campylobacter organisms were first isolated in the early 1900s from aborted sheep fetuses. However, it was not until the 1970s that Campylobacter were isolated from stool.

While there are many members of the genus Campylobacter, the major enteric pathogen for humans is Campylobacter jejuni, although Campylobacter coli, Campylobacter fetus, Campylobacter upsaliensis, and Campylobacter lari are also pathogenic to humans. C. jejuni is most frequently associated with GI disease, and C. fetus usually causes systemic infection, often in debilitated patients. Campylobacter are microaerophilic, and although all will grow at 37°C (98.6°F), C. jejuni grows best at 42°C (107.6°F). A number of selective media are in use for the detection of Campylobacter spp. and the organisms grow optimally in a gas mixture of 5% to 10% oxygen, 1% to 10% carbon dioxide, and some hydrogen. Growth may be present following overnight incubation, but 2 days are needed before a negative report can be issued.

Although several serotypes of C. jejuni have been reported, there are few data regarding the relative virulence of these different types, although some appear to be more closely associated with the development of Guillain–Barre´ syndrome (GBS) than others.