Coloured transmission electron micrograph (TEM) of the bacterium Helicobacter pylori (formerly known as Campylobacter pyloridis). This Gram-negative bacteria is curved in shape, or spiral, with flagella which make it highly motile. Here several flagella are visible. Colonies of H. pylori occur on the stomach mucous membrane in people suffering gastritis; this bacteria has been linked to stomach ulcer formation. H.pylori may also be a co-factor for gastric cancer; its presence in the stomach increases the chance of tumours occurring. Magnification: x10,400 at 6x4.5cm size.