Campylobacter jejuni bacteria. Coloured scanning electron micrograph (SEM) of a Campylobacter jejuni bacteria. Campylobacter jejuni is a Gram-negative slender, curved, and motile rod. It is a microaerophilic organism, which means it has a requirement for reduced levels of oxygen. Infection with Campylobacter jejuni is one of the most common causes of gastroenteritis worldwide; it occurs more frequently than do infections caused by Salmonella species, Shigella species, or Escherichia coli. Magnification: x10, 000, when printed 10cm wide.