Helicobacter pylori. Coloured transmission electron micrograph (TEM) of a Helicobacter pylori bacterium (formerly known as Campylobacter pyloridis). This Gram-negative bacillus bacterium is curved (as here) or spiral in shape, with flagellae for motility. Here, many hair-like flagellae are visible. Colonies of H.pylori occur on the stomach mucous membrane in people suffering gastritis, and this bacteria has been linked to stomach ulcer formation. H.pylori may also be a co-factor for gastric cancer; its presence increases the risk of stomach tumours. Magnification: 7,700 at 6x4.5cm size.