Researchers Identify Key Gene That Controls Emergence Of Salmonella

February 04, 1999

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 now know that this gene can be turned on or off depending on where the organism is growing. What we think is really important is that this gene or a master switch controlling this gene is really a key process in how salmonella makes a living in animals."

Isaacson reported salmonella's two genetic phenotypes in 1992. The new work sought to find the differences by comparing mutants with the two forms of the Salmonella typhimurium strain. Using antibiotic-resistant markers and a detection technique called SDS-polyacrylamine gel electrophoresis, they identified the RfaL gene that is required to produce O-antigen.

U. of I. scientists also have been looking on farms for reservoirs of salmonella. Their results suggest that the prevalance 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," Isaacson said. "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."
-end-


University of Illinois at Urbana-Champaign

Related Immune System Articles from Brightsurf:

How the immune system remembers viruses
For a person to acquire immunity to a disease, T cells must develop into memory cells after contact with the pathogen.

How does the immune system develop in the first days of life?
Researchers highlight the anti-inflammatory response taking place after birth and designed to shield the newborn from infection.

Memory training for the immune system
The immune system will memorize the pathogen after an infection and can therefore react promptly after reinfection with the same pathogen.

Immune system may have another job -- combatting depression
An inflammatory autoimmune response within the central nervous system similar to one linked to neurodegenerative diseases such as multiple sclerosis (MS) has also been found in the spinal fluid of healthy people, according to a new Yale-led study comparing immune system cells in the spinal fluid of MS patients and healthy subjects.

COVID-19: Immune system derails
Contrary to what has been generally assumed so far, a severe course of COVID-19 does not solely result in a strong immune reaction - rather, the immune response is caught in a continuous loop of activation and inhibition.

Immune cell steroids help tumours suppress the immune system, offering new drug targets
Tumours found to evade the immune system by telling immune cells to produce immunosuppressive steroids.

Immune system -- Knocked off balance
Instead of protecting us, the immune system can sometimes go awry, as in the case of autoimmune diseases and allergies.

Too much salt weakens the immune system
A high-salt diet is not only bad for one's blood pressure, but also for the immune system.

Parkinson's and the immune system
Mutations in the Parkin gene are a common cause of hereditary forms of Parkinson's disease.

How an immune system regulator shifts the balance of immune cells
Researchers have provided new insight on the role of cyclic AMP (cAMP) in regulating the immune response.

Read More: Immune System News and Immune System Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.