The first Nobel prize - one for medicine - goes to Barry Marshall and his collaborator Robin Warren from Australia for their discovery of Helicobacter pylori, the cause of most ulcers, in 1982. Because I happened to have studied this spiral-shaped bacteria for certain personal reasons roughly 8 years ago, I may say that these guys definitely deserve their award.
Don't panic: having Helicobacter pylori is by itself no big deal: one third of the people on the planet have it.
How can you say that their discovery was revolutionary? It's mainly because in their case, much like in lots of other examples in science, the Helicobacter pylori theory was ridiculed by the so-called "scientific consensus" promoted by scientists as well as doctors. The scientific consensus believed that no bacteria could live in the acidic stomach and the ulcers were always caused by stress, spicy food, and too much acid.
The following paragraph is brutal and should not be read by children.
What could Barry Marshall do to force the people to pay attention to their theory? Well, he drank a test tube of the bacteria and swiftly developed gastric ulcers, which he then cured by antibiotics. It was obviously very difficult to convince anyone. Fortunately, the times are changing, the people behind the "scientific consensus" are nowadays identified as a sort of anonymous morons, and Marshall and Warren may share their well-deserved one million of US dollars. And they became, of course, mainstream scientists.
Human stupidity repeats its mistakes all the time. This was not the first time when a microorganism was known to cause a disease but virtually all scientists humiliated the idea without having a good reason to do so. (And believe me that there are many examples in science that are not about microorganisms causing diseases.) In 1795, Alexander Gordon of Aberdeen figured out that the fever after the childbirth was probably an infectious disease that he could cure. The consensus said no. In 1843, Oliver Wendell Holmes presented convincing evidence that puerpetal fever was contagious. No. In 1849 Semmelweiss virtually eliminated the fever from his hospitals by better sanitary procedures. The consensus said that he was Jew and they even fired him. Only in the early 20th century, i.e. 150 years after the first discovery, people started to agree that the fever was infectious.