Strain-Dependent Responses of Listeria monocytogenes Biofilms to Combined Enzymatic and Bacteriocin Treatments

Abstract

Listeria monocytogenes forms resilient biofilms that protect cells from sanitizers and environmental stress, allowing the pathogen to persist in food processing environments. This study evaluated the combined effects of an engineered carbohydrate-active enzyme (CAase) and two food-grade bacteriocins, nisin and thermophilin 110 (T110), on biofilm disruption and cell inactivation. Biofilm biomass was quantified by crystal violet staining and visualized by microscopic imaging, with viable cells enumerated in treatment supernatants. Minimum inhibitory concentrations (MIC) for nisin (12.5–25 µg mL−1) and T110 (64 to 512 arbitrary units (AU) mL−1) were determined against all 11 L. monocytogenes strains, while CAase alone showed limited antimicrobial activity. CAase was shown to significantly reduce biofilm biomass, releasing embedded cells from the matrix. Nisin (25 µg mL−1) and T110 (1024 AU mL−1) were observed to decrease biofilm biomass and viable-cell recovery, but results were strain-dependent. Biofilm clearance improved for some L. monocytogenes strains when CAase was combined with either bacteriocin, but nisin was more effective at reducing the number of viable cells recovered. Results from this study demonstrated that enzymatic degradation of the extracellular matrix may enhance bacteriocin efficacy by improving access to target cells and support the potential of enzyme–bacteriocin combinations as food-safe biofilm control strategies in food production environments.