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Spring 1999 Vol.23 No.2
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"On/off" Gene for Salmonella Identified

by Jim Barlow

Dr. Richard Isaacson(picture)

Dr. Richard Isaacson in the Microbiology Lab.

A gene that dictates Salmonella's ability to live dormantly or cause disease in pigs has been found by College researchers. In the laboratory, Dr. Richard E. Isaacson, professor of veterinary pathobiology, and his coworkers even fooled the bacteria in one strain into switching back and forth between the two forms.

The finding is the first documentation that relates a phase-shifting process in Salmonella or other food-borne bacterium to its ability to grow in specific environments. Finding the control switch could pave the way for developing methods to rid the disease-causing form from farm animals. Salmonella attacks the 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," says Dr. Isaacson.

He and graduate student Lola Y. Kwan, now at Northwestern University, reported their finding in the December issue of Infection and Immunity.

Other researchers have been looking on farms for reservoirs of Salmonella. Their results suggest that the prevalence of Salmonella in swine herds is high, and that the pig is an important reservoir. "It does look like the most likely reservoir is the pig itself," notes Dr. Isaacson. "It may be that the only real solution is a biotechnological approach that would trick Salmonella into turning itself off so it could be naturally cleared from the pigs."

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