A study just published in the International Journal of Food Microbiology examined the survival rates of free-floating cells of salmonella enterica Tennessee versus those in biofilm form when stored in dry milk powder for up to 30 days.
In such a dry environment, pathogens cease to reproduce, but adhere to surfaces and produce a biofilm that protects them from a harsh environment when placed in such a dry environment. Experts disagree over whether pathogens prompted to produce biofilms in this way are more or less likely to survive passage into the human intestine and thus more likely to cause illness.
"Biofilms are becoming an increasing problem within the food industry due to their ability to adhere to surfaces and withstand current sanitation practices," the paper states.
Low moisture foods
At various points during the study, the Salmonella was tested in a simulated gastrointestinal system. It survived this long-term storage in large numbers but the biofilm Salmonella proved more resilient than the free-floating cells.
The researchers from US institute Virginia Tech also said the bacteria's stress response to the dry conditions made it more likely to cause disease. And they added that biofilms allowed the Salmonella to survive the harsh, acidic environment of the gut, increasing its chances of reaching the intestines.
Outbreaks of Salmonella associated with dried foods such as nuts, cereals, spices, spices, powdered milk and pet foods have been associated with more than 900 illnesses in the past five years, the scientists claimed. These foods were previously thought to be safe, because their dry nature would protect them from microbial growth.
'Increasing problem'
"Biofilms are an increasing problem in food processing plants serving as a potential source of contamination," said Monica Ponder, an assistant professor of food science and technology in Virginia Tech's College of Agriculture and Life Sciences.
"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."
One out of every six Americans becomes ill from eating contaminated food each year, with more than a million illnesses caused by salmonella enterica bacteria, according to the Centers for Disease Control and Prevention. These illnesses account for 35% of hospitalisations and 28% of deaths, according to the Virginia Tech researchers.
Source: 'Biofilms promote survival and virulence of Salmonella enterica sv Tennessee during prolonged dry storage and after passage through an in vitro digestion system', International Journal of Food Microbiology, Volume 162 issue 3, April 1, 2013, pp252-259; doi: 10.1016/j.ijfoodmicro.2013.01.026.
Authors: Bryan Aviles, Courtney Klotz, Joseph Eifert, Robert Williams, Monica Ponder, , Department of Food Science and Technology, Virginia Tech