Title: Listeria monocytogenes Biofilm Formation on Silver Ion Impregnated Cutting Boards Authors
Submitted to: Food Protection Trends
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 23, 2009
Publication Date: March 1, 2010
Citation: Berrang, M.E., Frank, J., Meinersmann, R.J. 2010. Listeria monocytogenes Biofilm Formation on Silver Ion Impregnated Cutting Boards. Food Protection Trends. 30(3): 168 - 171. Interpretive Summary: Listeria monocytogenes is a human pathogen that may be present in poultry processing plants and can attach and grow on food processing surfaces as a biofilm. This organism can be transferred from a biofilm on a food contact surface to the food product itself, creating a potential for human illness. Silver ions have antibacterial activity and can be immobilized in the formulation of plastic cutting boards in an effort to kill bacteria on the board surface. We tested the ability of L. monocytogenes to attach and grow on the surface of silver ion treated plastic cutting boards. Cutting boards with and without the incorporation of silver ions were exposed to L. monocytogenes under conditions suitable for formation of a biofilm. Numbers L. monocytogenes attached to the cutting boards were determined immediately after biofilm formation, and following a further 24 h exposure to the silver treatment. We found that silver ions made no difference in the attachment or survival of L. monocytogenes which was present at levels of more than 1 million cells per square centimeter initially and close to 10,000 per square centimeter after 24 hour, on both treated and control cutting boards. We further tested the ability of a meat spoilage organism, Pseudomonas putida to form biofilms on the cutting boards. Like L. monocytogenes, P. putida formed biofilms equally well on both types of cutting boards. Under the conditions of these tests, silver ion treatment did not render a cutting board more resistant to bacterial attachment or growth. These data will be useful to food processors as they make decisions regarding purchasing plastic food contact surfaces with antimicrobial additives.
Technical Abstract: Listeria monocytogenes is a human pathogen that can be a member of a biofilm community attached to surfaces in poultry processing plants. When present as a biofilm on product contact surfaces, this organism can effectively cross contaminate fully cooked ready-to-eat meat. Plastic cutting boards can be formulated to include antibacterial agents such as silver ions. In this study we compared the ability of L. monocytogenes to attach and form a biofilm on identical plastic cutting boards manufactured with and without silver ions. Cutting boards were cut into 2 by 2 cm squares and inoculated with a poultry plant isolate of L. monocytogenes known to effectively form biofilms. Inoculation was conducted by submersion in a cell suspension of approximately 108 cells per mL PBS for 2 hours. All pieces were then washed in PBS to remove unattached cells and incubated in dilute (1/10) brain heart infusion broth for 24 hours at 25o C. Un-attached cells were again removed by washing in PBS. The surface was sampled using a pre-moistened sterile cotton swab either immediately after removal of un-attached cells or after a 24 hour dry exposure of attached cells to the board formulation at 25o C. Three replications were conducted with five cutting board squares for each treatment in each replication (n=15). When sampled immediately after washing, similar numbers were recovered from treated and untreated boards: 6.83 and 6.86 log cfu/cm2 respectively. Twenty four hour dry time lessened the density of viable attached L. monocytogenes on both types of cutting boards to the same degree; silver ion impregnated boards had 3.95 log cfu/cm2 while un-treated control boards had 3.97 log cfu/cm2. Under the conditions of these tests, silver ion impregnation did not lessen the ability of L. monocytogenes to form a biofilm on the surface of plastic cutting boards.