Coloured transmission electron micrograph (TEM) of the bacteria Helicobacter pylori (formerly known as Campylobacter pyloridis). This Gramnegative 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 cofactor for gastric cancer; its presence in the stomach increases the chance of tumours occurring. Magnification: x6000 at 6x4.5cm size.