^BHelicobacter pylori. ^b Coloured transmission electron micrograph (TEM) of a ^IHelicobacter ^Ipylori^i bacterium (formerly known as ^ICampylobacter ^Ipyloridis^i). 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 ^IH.pylori^i occur on the stomach mucous membrane in people suffering gastritis, and this bacteria has been linked to stomach ulcer formation. ^IH.pylori^i may also be a co-factor for gastric cancer; its presence increases the risk of stomach tumours. Magnification: 7,700 at 6×4.5cm size.