MICROBIAL FOOD SAFETY OF FRESH AND FRESH-CUT PRODUCETitle: Osmoregulated periplasmic glucans are needed for competitive growth and biofilm formation by Salmonella enterica serovar Typhimurium in leafy-green vegetable wash-waters and colonization in mice
Submitted to: FEMS Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 13, 2008
Publication Date: December 24, 2008
Citation: Liu, L., Tan, S., Jun, W., Smith, A.D., Meng, J., Bhagwat, A.A. 2008. Osmoregulated periplasmic glucans are needed for competitive growth and biofilm formation by Salmonella enterica serovar Typhimurium in leafy-green vegetable wash-waters and colonization in mice. FEMS Microbiology Letters. 292:13-20.
Interpretive Summary: The ability to survive under low nutrient conditions in the environment enables Salmonella spp. to successfully enter the food chain. We discovered that Salmonella enterica serovar Typhimurium strains form a mucuous-like substance (biofilm) under poor growth conditions such as in vegetable wash waters. Survival of human pathogens in biofilms is a persistent cause of food borne infections. We have identified a small molecular weight sugar compound in Salmonella spp. which is essential for biofilm formation. Genetic mutation in the corresponding gene rendered Salmonella strains incapable of forming biofilms. Identification of genes essential for biofilm formation is a crucial in designing specific sanitation agents which will be more effective in removing biofilms. The development of better cleaning agents to eliminate Salmonella spp.in food would be extremely beneficial to the food processing industry.
Osmoregulated periplasmic glucans (OPGs) are major periplasmic constituents of Gram negative bacteria. The role of OPGs has been postulated in symbiotic as well as pathogenic host-microbe interactions. Here we report the role of OPGs from Salmonella enterica serovar Typhimurium during growth and biofilm formation in leafy-green vegetable wash water. The opgGH mutant strain which was defective in OPGs biosynthesis grew at a slower rate in wash-water obtained from spinach, lettuce and green collard and severely impaired biofilm formation. The lack of OPGs synthesis did not influence biofilm formation by the opgGH mutant in laboratory media. In co-culture experiments performed either in the planktonic or biofilm state, the wild-type cell population was 10-fold greater than that of the opgGH mutant. The opgGH mutant strain was also a poor competitor in colonizing mice organs when introduced orally along with the wild type strain. This is the first report demonstrating the role of OPGs of Salmonella in competitive colonization of biofilms, planktonic cultures and mice organs.