P1-162 Effect of Disinfectants on the Biofilm Formation Capacity of Listeria monocytogenes Isolated from Ready-to-Eat (RTE) Meat Products

Monday, July 10, 2017
Exhibit Hall (Tampa Convention Center)
Mauricio Redondo , University of Costa Rica , San José , Costa Rica
María Arias-Echandi , University of Costa Rica , San Pedro , Costa Rica
Introduction: Listeria monocytogenes is an opportunistic human pathogen, capable of growing at low temperatures (4°C), that a recognized capacity to form biofilms on food contact surfaces. Listeria monocytogenes cells present in biofilms may be more resistant to common disinfectants used at the retail level.

Purpose: The purpose of this study was to evaluate the effect of commonly use disinfectants (chlorine and quaternary ammonium) on the capacity of L. monocytogenescells to establish viable biofilms.

Methods: The biofilm formation capacity of four different L. monocytogenes strains was assessed using the plastic microtiter technique. Bacterial cells inoculated into Tryptic Soy Broth (TSB) and peptone water (PW) were exposed to different concentrations of chlorine (200, 300, and 500 ppm) and quaternary ammonium (200, 400, and 600 ppm) for different periods of time (2-6 min). Biofilms were measured by optical density after incubation at 37°C and staining with crystal violet. The reduction of a tetrazolium salt was used to determine the viability of preformed biofilms after exposure to the same antimicrobials. Replicates of the optical density results were analyzed and compared with ANOVA.

Results: Three of the isolates showed higher optical densities (p<0.05) after exposure to high concentrations of chlorine (300 ppm) and quaternary ammonium (600 ppm) for 6 minutes. However, these optical densities were lower (p<0.05) in comparison to the controls (no antimicrobials) and the isolates were classified as moderate biofilm producers. None of the isolates established biofilms in PW. A higher metabolic activity (p<0.05) was observed in the biofilms established by the same isolates; however, some minor activity was observed for other isolates as well.

Significance: These data suggest that disinfection practices in meat stores (type and concentration of disinfectants) may not control the presence of L. monocytogenes in these environments.