This study was performed to evaluate the effectiveness of benzalkonium chloride combined with ultrasound in eliminating Listeria monocytogenes biofilm from polystyrene surface. The test strain of L. monocytogenes, previously classified as strong biofilm producer, was grown to form biofilm in tryptic soy broth at 20°C for 6 days in polystyrene specimen containers. The biofilms formed on surface of containers were treated with ultrasound alone, benzalkonium chloride (100 and 400 mg l−1) alone and their combination for three different exposure times (1, 5 and 15 min) at room temperature. Sonication was performed using an ultrasound bath at a constant ultrasound frequency of 35 kHz. After treatments, levels of biofilm biomass and viable cells in biofilm were determined using crystal violet staining and XTT assays, respectively. The combined treatment of ultrasound and benzalkonium chloride resulted in significant (P < 0·05) more decrease in the level of viable cells in the L. monocytogenes biofilm compared to individual treatments of benzalkonium chloride. Our results suggest that the combination of benzalkonium chloride with ultrasound is useful approach for the elimination of L. monocytogenes biofilms from plastic surfaces.Significance and Impact of the Study
Listeria monocytogenes is capable of adhering and forming biofilm on inert surfaces such as plastics. Biofilms are more resistant to disinfectants compared to planktonic cells, and this makes their elimination from food processing facilities a big challenge. Moreover, the emergence of resistant to disinfectants bacteria clearly shows that new biofilm control strategies are required. Among new strategies, the ultrasound treatment attracts attention as a nonchemical and environmentally friendly technology. This study demonstrated that the combination of ultrasound and benzalkonium chloride is a feasible strategy for removal of L. monocytogenes biofilms from plastic food-contact surfaces.