Helicobacter pylori is a
gram-negative bacterium that lives inside the mucus lining of the
stomach. It belongs among the
proteobacteria. Many
gastric ulcers are caused by
H. pylori infection, although most humans are infected and not all infections lead to symptoms. Two strains of
H. pylori have been
sequenced.
Information on ulcers and H. pylori (http://www.cdc.gov/ulcer/) at the Centers for Disease Control and Prevention.