Peptic ulcers can be caused by factors such as hyper acid secretion and bacterial infection. Helicobacter pylori is the specific bacterium that is known to be the causative agent for peptic ulcers.

Option 1: Helicobacter pylori - This is the correct answer. Helicobacter pylori is a common bacterium that is found in the stomach and is responsible for causing most cases of peptic ulcers. It is estimated that about 80% of peptic ulcers are caused by H. pylori infection. The bacterium can survive in the acidic environment of the stomach and can irritate and damage the lining, leading to the formation of ulcers.

Option 2: E. coli - This bacterium is not typically associated with the development of peptic ulcers. E. coli infection usually causes gastrointestinal symptoms such as diarrhea and abdominal pain.

Option 3: Streptococcus pneumoniae - While Streptococcus pneumoniae is a bacterial pathogen that can cause various infections, including respiratory and invasive diseases, it is not associated with the development of peptic ulcers.

Option 4: Salmonella typhimurium - Salmonella typhimurium is a type of bacteria that can