An international team of researchers has advanced the prospects for a vaccine to prevent ulcers and stomach cancer. They have discovered how the bacterium that causes these disorders attacks the stomach lining.

An organism known as Helicobacter pylori causes most stomach ulcers and has been linked to stomach cancer, the fifth most common cancer in the world. Infection with this microbe is very common. A U.S. government expert on the organism, physician Andre Dubois, said it is far more common in developing countries than in North America and Europe. "Helicobacter pylori is currently infecting over half the world's population, and therefore it must a smart microbe in order to do that," he said. "Only one other bacterium, the one that causes cavities and is colonizing the gums, is more prevalent in the world compared to Helicobacter pylori."

Now, Dr. Dubois of the Uniformed Services University of the Health Sciences near Washington and a group of Swedish, Estonian, and French scientists have learned how the bacterium sticks to the stomach lining.

They found that as Helicobacter pylori burrows into it, the cells of the lining begin their defense. They produce a sugar molecule that serves as a flag to attract immune cells to fight the infection.

But the sugar production has an unintended outcome. As the researchers report in the journal "Science," the infecting microbe displays a protein molecule that binds to the sugars, giving it a stronger bite on the stomach.

Dr. Dubois said the work builds on earlier studies in which the researchers identified the stomach lining molecules to which the microbe first attaches before it grips the sugars. "In addition to that first attachment that occurs between the body and the microbe through a specialized structure, a second one is then used by the microbe to attach in a better way and perhaps in a closer way that allows it to feed better on the stomach."

Scientists believe Helicobacter pylori infection begins in infancy and last for decades. The new findings could help explain why it is so durable. Only 10 to 15 percent of all who have it become ill, but that is still a huge number of people considering how common it is.

The researchers say the newly-found protein on the bacterium could be the basis for a vaccine to provoke an immune response to prevent infection. Since the protein is unique to this microbe, the immune response would not affect the many other types of bacteria that are beneficial in the stomach.

The scientists also say that better understanding the infection process could lead to new drugs to treat it. Antibiotics are now used, but with the infection so widespread, overuse could promote resistant strains of the bacterium that only new drugs could conquer.