During the '80s and '90s, I was working at the University of Virginia Department of Immunology, where Barry Marshall, the doctor who discovered this, was working. He was somewhat mocked for a period of time, even in the university community, before his proposal that H. pylori is the major cause of ulcers was shown to be accurate. Pushback from pharmas, of course, as it eliminated the lifetime addiction to antacid formulations, in favor of simple antibiotic treatment.
He shared the Nobel Prize in Medicine in 2005 for this discovery, along with an Australian colleague. Marshall, with no stomach problems, actually drank a solution containing H. pylori, demonstrated that the bacterium infected his tissues, and then eliminated the bacterium with antibiotics. A classic example of the use of Koch's Postulates.