Helicobacter pylori. Coloured Scanning Electron Micrograph (SEM) of Helicobacter pylori bacter- ia, the cause of stomach ulcers. These Gram- negative bacilli bacteria (pink) are curved or spiral in shape, and have tail-like flagellae for motility. They are seen here on the mucus membrane (mucosa) that lines the stomach. Colonies occur on the stomach mucosa in people suffering from stomach ulcers (peptic ulcers). The species may also be linked to cancer of the stomach. Magnification: x4000 at 7x6cm size.