Inhibitory Effect of DNase–Chitosan–Nisin Nanoparticles on Cell Viability, Motility, and Spatial Structures of Listeria monocytogenes Biofilms

<i>Listeria monocytogenes</i> biofilm contamination on food contact surfaces is a major concern for the food industry. Nanoparticle encapsulation appears as a novel strategy for food surface disinfection to prevent biofilm formation. Chitosan nanoparticles loaded with nisin and DNase I (DNase-CS-N) have been constructed to exhibit antimicrobial activity against <i>L. monocytogenes</i>. This study aimed to investigate their ability to inhibit <i>L. monocytogenes</i> biofilm formation and eliminate preformed biofilms on food contact surfaces (polystyrene, polyurethane, and stainless steel). DNase-CS-N could decrease 99% and 99.5% biofilm cell numbers at 1/2 MIC and MIC, respectively. At sub-MICs, DNase-CS-N could reduce cell motility (swimming and swarming) and slime production of <i>L. monocytogenes</i>. In terms of effect on biofilm elimination, DNase-CS-N at the concentration of 4 MIC led to 3-4 log reduction in biofilm cells in preformed biofilms, performing higher efficiency compared with other treatments (CSNPs, CS-N). Furthermore, the three-dimensional structure of <i>L. monocytogenes</i> biofilms was severely disrupted after DNase-CS-N treatment, with bacterial cells scattered on the surface. The morphology of biofilm cells was also greatly damaged with wrinkled surfaces, disrupted cell membranes, and leakage of intracellular nucleic acids and proteins. These results indicate the potential applicability of DNase-CS-N for inhibiting and eliminating <i>L. monocytogenes</i> biofilms on food contact surfaces.