H. pylori
1) What is it? Helicobacter pylori (H. pylori) is a type of bacteria. These germs can enter your body and live in your digestive tract. After many years, they can cause sores, called ulcers, in the lining of your stomach or the upper part of your small intestine. For some people, an infection can lead to stomach cancer.

2) What do H. pylori cause in humans?
H. pylori infections start with a person acquiring the bacterium from another person (via either the fecal-oral or oral-oral route). Although the majority of individuals that have these bacteria in their GI tracts have few if any symptoms (see symptoms), most people develop stomach inflammation (gastritis) from the body's response to the bacterium itself and to a cytotoxic termed Vac-A, a chemical that the bacterium produces. Researchers also suggest that the stomach acid stimulates the bacterium in addition to the cytotoxic, and increases invasion of the lining of the stomach, inflammation, and ulcer formation. Other investigators have shown that these bacteria and their products are associated with alterations in the cells lining the stomach that when altered are associated with stomach and other cancers, although these are infrequently seen diseases.

3. Symptoms and signs
Most individuals infected with H. pylori have few or no symptoms. Some may experience a few episodes of gastritis like: minor belching, bloating, nausea, vomiting, and abdominal discomfort.
Often, these symptoms simply go away. However, those individuals who have a more serious infection exhibit symptoms of stomach and duodenal ulcers or gastritis which include the following: abdominal pain and/or discomfort that usually does not wax and wane nausea and vomiting sometimes with blood or coffee-ground like vomitus dark or tar-like stools (black color of feces due to bleeding ulcers) fatigue low red blood cell count due to bleeding full feeling after a small amount of food decreased appetite that is more