May 24 (HealthDay News) -- A high-salt diet may increase the risk of developing gastric and duodenal ulcers, a U.S. study finds.

Researchers found that high concentrations of salt in the stomach appear to induce gene activity in the ulcer-causing Helicobacter pylori bacterium that causes it to become more virulent. About 20 percent of Americans age 40 and about 50 percent of those over age 60 are infected with H. pylori, but only a small percentage of them develop ulcers.

"Apparently the stomach pathogen H. pylori closely monitors the diets of those people whom it infects. Epidemiological evidence has long implied that there is a connection between H. pylori and the composition of the human diet. This is especially true for diets rich in salt," researchers Hanan Gancz, of the Uniformed Services University of the Health Sciences in Bethesda, Md., said in a prepared statement.

"We noted that H. pylori growth rate shows a sharp decline at high salt concentrations. Moreover, bacterial cells exposed to increased salt exhibited striking morphological changes: Cells became elongated and formed long chains," Gancz said. "We conclude that H. pylori exposed to high levels of salt in vitro exhibit a defect in cell division."

The researchers also found that high-salt conditions increased transcription of two genes responsible for the virulence of H. pylori.

"The altered expression patterns of some virulence genes may partially explain the increased disease risk that is associated with a high-salt diet in H. pylori infected individuals," Gancz said.

The findings were to be presented Tuesday at the American Society for Microbiology's general meeting in Toronto.