Salmonella Can Survive Even In Dry Conditions
April 12, 2013

Protective Coatings Of Biofilms Help Salmonella Survive

redOrbit Staff & Wire Reports - Your Universe Online

Groups of microorganisms known as biofilms, which cling to surfaces and build protective coatings, have helped make the human pathogen Salmonella more resistant to the protective measures that could help prevent outbreaks from occurring, researchers from Virginia Tech claim in a new study.

Salmonella bacteria, which the CDC reports causes over one million Americans to fall ill each year, has become more resistant to heat-processing and sanitizers such as bleach because of the biofilms, researchers from the Fralin Life Science Institute explain in the April issue of the International Journal of Food Microbiology.

In addition, the microorganisms have helped protect Salmonella from extremely dry conditions, as well as normal human digestive processes, the Blacksburg, Virginia-based university´s researchers added.

“Biofilms are an increasing problem in food processing plants serving as a potential source of contamination,” Monica Ponder, an assistant professor of Food Science and Technology in the Virginia Tech College of Agriculture and Life Sciences, said in a statement Wednesday.

“We have discovered that Salmonella in biofilms survive on dried foods much better than previously thought, and because of this are more likely to cause disease,” she added.

Over the past five years, more than 900 Salmonella-related illnesses have been linked to dried foods such as nuts, cereals, spices, powdered milk and pet foods. Those foods were previously believed to have been safe from the bacteria, as their dry nature helps halt the growth of bacteria and other microbes.

“Most people expect to find Salmonella on raw meats but don't consider that it can survive on fruits, vegetables or dry products, which are not always cooked,” Ponder said.

Salmonella typically thrive and reproduce abundantly in moist conditions, the researchers said. In dry conditions, they cease reproduction, but activate genes which produce biofilms, thus protecting them from the harsh conditions.

“Researchers tested the resilience of the Salmonella biofilm by drying it and storing it in dry milk powder for up to 30 days,” the university explained. “At various points it was tested in a simulated gastrointestinal system. Salmonella survived this long- term storage in large numbers but the biofilm Salmonella were more resilient than the free-floating cells treated to the same conditions.”

“The bacteria´s stress response to the dry conditions also made it more likely to cause disease,” they added. “Biofilms allowed the Salmonella to survive the harsh, acidic environment of the stomach, increasing its chances of reaching the intestines, where infection results in the symptoms associated with food poisoning.”

The researchers believe that their work could help the US Food and Drug Administration (FDA) shape federal regulations by emphasizing the need for a new strategy to reduce biofilm formation on equipment. With luck, those strategies, along with improved sanitation techniques, will hopefully decrease the likelihood of another widespread Salmonella outbreak in the US.