CHAMPAIGN, Ill. -- A gene that dictates salmonella's ability to live dormantly or cause disease in pigs has been found by researchers at the University of Illinois. In the laboratory, the scientists even fooled the bacteria in one strain into switching back and forth between these two forms.
The finding, says Richard E. Isaacson, a professor of veterinary pathobiology, is the first documentation of a phase-shifting process in salmonella and in any food-borne bacteria that is related to its ability to grow in specific environments. Finding the controlling switch, he said, could pave the way for developing methods to rid the disease-causing form from farm animals.
Salmonella attacks the stomach and intestines in animals and humans, and is a leading cause of gastrointestinal infections. Some 2,000 strains have been identified. Until now, scientists have not been able to explain why salmonella is often found in apparently healthy animals.
"We think that the reason that animals can appear healthy but go on with long-term infection is because the bacteria switches back and forth between these two forms, so that it has just the right combination of the right kind of cells to survive and linger there but not cause disease," Isaacson said.
Isaacson and graduate student Lola Y. Kwan, now at Northwestern University, reported their finding in the December issue of the journal Infection and Immunity. The work -- funded by the U.S. Department of Agriculture -- points to a sugar-containing substance known as O-antigen that sits on the outside of the bacterial cell. When produced inside an animal, salmonella cells become less visible to the immune system and cause illness as levels increase. The other version, normally found in the environment, lacks O-antigen and is easily removed when detected by the immune system once inside.
"What we have identified is an important gene that is involved in the ability of
salmonella to cause disease,"
Isaacson said. "We n
Contact: Jim Barlow, Life Sciences Editor
University of Illinois at Urbana-Champaign