An unusual regulatory mechanism that controls the swimmer/non-swimmer option in genetically identical Salmonella also impacts the bacteria's ability to cause infection.
University of Washington scientists reported the discovery this week in the Proceedings of the National Academy of Sciences.
As Salmonella divides into genetically identical clones, either of the two forms of the bacteria can emerge. Some individuals sport flagella thin, whip-like projections that propel the bacterium. Others do not.
When grown in a lab dish, both types appear.
Salmonella is a common food-poisoning bacteria. It can survive and take hold in hostile environments like inside of people who are protected by hoards of infection-fighting cells. In immunocompromised individuals, it causes blood stream infections.
"In an unpredictable world," said Dr. Brad Cookson, professor of microbiology and laboratory medicine, and division head of Clinical Microbiology at the UW, "Salmonella have evolved to hedge their bets." Each guise has its own advantages and drawbacks in invading a host and evading defenses, depending on the situation.
Cookson explained that being genetically the same but differing in appearance and function is useful for a population of disease-causing bacteria. Even though the bacteria might be identical clones, varying characteristics of the individuals some of whom are mobile and some of whom are stationary -- allows the population to colonize a host and establish an infection.
"Diversity," Cookson noted, "improves the chance that some of the clones will thrive in fluctuating environments." To infect an animal, swallowed Salmonella breaches the protective mucous of the gut, colonizes the lymph tissues, and then builds a niche inside germ-killing cells. These cells are co-opted into ferrying the Salmonella to the spleen and other organ system tissue
|Contact: Leila Gray|
University of Washington