2. H. pylori bacteria.
Helicobacter (H.) pylori bacteria often live within the mucous layer that runs along and protects the delicate tissues that line the interior of the small intestine and the stomach. Typically, this bacteria does not cause any issues; in fact, most people who become infected with H. pylori bacteria never experience any symptoms. However, in some cases, an infection of H. pylori bacteria can lead to an inflammation of the interior lining of the stomach, which can result in the formation of a gastric ulcer.
The cause of the spread of an H. pylori bacterial infection is not understood; however, medical experts and scientists do believe that it may be transmitted from one individual to another via close contact; kissing, for example. It is also believed that infections of H. pylori bacteria can be transmitted through diet, when food and water that contain the bacteria is consumed.