Helicobacter pylori bacterium, coloured transmission electron micrograph (TEM). This section through the bacterium shows its rod-shaped body and several flagella (upper right, used for movement). H. pylori (formerly named Campylobacter pyloridis or pylori) is a bacterium that infects the mucosal stomach lining. Some people then go on to develop stomach ulcers and gastritis due to the infection. Long-term infection is thought to be a risk factor for stomach cancer. The bacterium drills through the mucus layer and attaches to the stomach epithilial cells. Magnification: x15,800 when printed 10cm high.