Salmonella’s Protection Switch

The elusive foodborne pathogen Salmonella Typhimurium has developed a unique self-protective mechanism that responds to changes in the environment during its infective period, which may protect it from harm, according to new research from scientists at Pacific Northwest National Laboratory (PNNL) in Richland, Wash.

The research team grew Salmonella bacteria in two settings: Either with rich food that satisfied all their nutritional needs, or in a nutrient-depleted environment that mimicked the conditions the bug faces when infecting a host. What they found was “very surprising,” says Josh Adkins, PhD, director of PNNL’s Systems Biology Center for Enteral Pathogens.

“We thought we might see some changes or modifications on an individual protein level,” he says. Instead, there was a complete binary switch in what’s known as S-thiolation modifications, which protect a protein’s sulfur atoms. Dr. Adkins and his team found that in the well-nourished environment, Salmonella’s sulfur atoms were covered by a glutathione, while stressed-out, nutrient poor Salmonella switched to cysteines.

“We didn’t expect to see such a complete switch when the pathogen went from one state to another,” Dr. Adkins says. “Post-translational modifications are usually more like going from 5 percent one way to 20 percent, but in this case, these proteins are either fully one way or fully another.”

He suggests that this finding—which appears unique to Salmonella, and did not appear in other pathogens, such as E. coli—could point to possible preventive strategies. “Potentially there are ways we could block the transporter with a surface spray,” he says. “Or maybe we can prevent the infection in the food stock, so that it’s knocked down to the point that it doesn’t cause disease. At the same time, if you’re looking at contaminated meat, you might potentially be able to think of a treatment that’s not harmful to us but that would inhibit bacterial growth in general.”


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