Listeria monocytogenes biofilm formation on silver ion impregnated cutting boards

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 cross contaminate 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. Boards were inoculated by submersion in a cell suspension of approximately 108 cells per mL PBS for 2 hours at 25°C. All pieces were then rinsed in PBS to remove unattached cells and incubated in dilute (1/10) brain heart infusion broth for 24 hours at 25°C. Unattached cells were again removed by rinsing in PBS. The surface was sampled using a pre-moistened sterile cotton swab either immediately after removal of unattached cells or after a 24-hour dry exposure of attached cells to the board formulation at 25°C. The experiment was replicated three times, using five cutting board squares for each treatment in each replication (n=15). When surfaces were sampled immediately after rinsing, similar numbers of L. monocytogenes were recovered from treated and untreated boards: 6.83 and 6.86 log CFU/cm2, respectively. A twenty-four hour dry time reduced the number 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 untreated 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.