Light micrograph of a colony of the bacterium Helicobacter pylori (formerly called Campylobacter pylori), isolated from stomach tissue. H. pylori is a curved, or spiral, Gram-negative bacillus, equipped with flagella at one end (not visible in this section) that make it highly motile. Helicobacter pylori has recently been linked with the formation of stomach ulcers, through observation of the bacterium in biopsy specimens from patients with active chronic gastritis and peptic ulcers. Magnification: x1000 at 35mm size.