Salt and Organic Acids May Increase Pathogen Virulence
Salt and organic acids may increase the virulence of Listeria monocytogenes, one of the most harmful food-borne pathogens plaguing the U.S. today, say researchers from New York. They report their findings in the August 2006 issue of the journal Applied and Environmental Microbiology.
L. monocytogenes is attributed to 28% of all deaths in the U.S. related to food-borne illnesses. Foods considered to be at greatest risk for transmission are ready-to-eat products (RTE), with RTE meat products being the single most common cause of human infection. Researchers believe L. monocytogenes can grow in refrigerated temperatures and in the presence of organic acids and salt, indicating that exposure to certain environmental stress conditions may in fact enhance the organism's survival and induce expression of virulence genes.
In the study researchers measured the effects of temperature (7 or 37 degrees Celsius), pH (5.5 or 7.4), and the presence of salt and organic acids on the ability of L. monocytogenes to grow, invade cells, and survive exposure to synthetic gastric fluid. Results showed that the ability of L. monocytogenes to invade cells is affected by all elements with highest invasion occurring at 37 degrees Celsius and a pH level of 7.4. Although salt and organic acids appear to increase virulence during cell invasion, they alternately reduce the bacterium's ability to survive exposure to gastric fluid.
"Our results suggest that environmental stress conditions from specific foods may influence the L. monocytogenes infectious dose and thereby contribute to the association of food-borne infections with specific foods," say the researchers.
(M.R. Garner, K.E. James, M.C. Callahan, M. Wiedmann, K.J. Boor. 2006. Exposure to salt and organic acids increases the ability of Listeria monocytogenes to invade Caco-2 but decreases its ability to survive gastri
Contact: Carrie Patterson
American Society for Microbiology