The bacteria that is most strongly linked with gastric ulcer formation is H. pylori.
Helicobacter
Yes; ulcers are caused by the H. pylori bacterium which can certainly occur in children.
H. pylori is the bacteria associated with peptic ulcer disease and gastric cancer.
In a sense, a stomach ulcer (gastric ulcer, in medical terms) can be thought of as "the stomach eating itself." Helicobacter pylori is a bacterium associated with stomach ulcers.
niacin
Smoking does not cause ulcer formation, but it does cause gastritis, and does cause delayed healing of ulcers.
Barry J Marshall and J Robin Warren
Certain foods can indeed aggravate ulcers, but food does not cause them - they are caused by a bacterium called heliobactor pylori. Gastritis - a very different thing from ulcers - can be caused by any particularly spic, greasy or heavy food.
The link between bacterium H. Pylori and gastric ulcers was suspected for a long time, but finally proven in an unscientific way by scientist Barry Marshall (1981) who was fed up of not being able to confirm the link so drank a cup full of the bacterium and developed an ulcer a few days later.
He and his partner,Barry Marshall, discovered that bacterium was the cause of stomach ulcers, and re-discovered Helicobacter pylori
unicellular, however sometimes they are associated in groups or long strings.
Helicobacter pylori is a bacterium that lives in the mucous tissues that line the digestive tract. Infection with H. pylori is the most common cause of duodenal ulcers.
The bacterium most commonly associated with infection of the bile ducts is Escherichia coli