The discovery that bacteria rather than stress cause stomach ulcers and that antibiotics can cure the condition has won this year's Nobel prize in physiology or medicine.

Two Australian scientists who isolated the microbe responsible for peptic ulcers and were the first to show the condition is infectious were yesterday jointly awarded the £1m prize.

In 1982, Robin Warren, a pathologist at the Royal Perth Hospital, was the first to show that patients with chronic ulcers also tended to harbour colonies of bacteria in their stomachs.

Barry Marshall, a researcher at the University of Western Australia, became interested in Professor Warren's findings and initiated the studies that led to the identification of the bacterium responsible, which they named Helicobacter pylori.

Dr Marshall went on to test the theory personally by deliberating exposing himself to the bug and so triggering a bout of acute gastric illness in his own stomach.

Until the two scientists carried out their pioneering research, it was widely believed that nothing could live in the extremely acid environment of the stomach, and that ulcers and gastritis were the result of lifestyle and stress.

Professor Warren said it took a decade for others to accept their findings. "Everybody believed there were no bacteria in the stomach. When I said they were there, no one believed it," he said.

The Nobel Assembly at the Karolinska Institute in Stockholm said the two scientists showed that it was possible to cure rather than simply treat the symptoms of stomach ulcers.

"Thanks to the pioneering discovery of Marshall and Warren, peptic ulcer disease is no longer a chronic, frequently disabling condition, but a disease that can be cured by a short regimen of antibiotics and acid secretion inhibitors," the assembly said.

The two scientists managed to challenge prevailing dogmas with tenacity and a prepared mind, the assembly said. They presented an irrefutable case that the bacterium H. pylori is the cause of the disease, it added.

Dr Marshall's first attempt at culturing the bacterium failed and it was only after he had left the bug in the laboratory over an Easter holiday that he achieved success.

Lord May of Oxford, president of the Royal Society in London, said the work of the two scientists produced one of the most radical and important changes in the past 50 years in the perception of a medical condition.

"Their results led to the recognition that gastric disorders are infectious diseases, and overturned the previous view that they were physiological illnesses," Lord May said.

"In 1985, Marshall showed by deliberately infecting himself with the bacterium Helicobacter pylori that it caused acute gastric illness. This extraordinary act demonstrated outstanding dedication and commitment to his research," he said.

Professor Brian Spratt, a molecular microbiologist at Imperial College in London, said: "Drug companies had to radically change their approach from containing ulcers with antacids to treating with antibiotics. Ulcers predispose people to gastric cancer - so antibiotics also prevent cancer."