Enhancing antimicrobial activity of lysozyme against Listeria monocytogenes using immunonanoparticles

The antimicrobial efficacy of lysozyme may be reduced by undesirable interactions with food components and nontarget bacteria. Immunonanoparticles, i.e., nanoparticles functionalized with pathogen-specific antibodies, may serve as an antimicrobial carrier for improving the stability and activity of antimicrobials in foods. The objective of this research was to study the antimicrobial activity of lysozyme-carrying immunonanoparticles against Listeria monocytogenes. Polystyrene nanoparticles with active carboxyl groups were conjugated with anti-L. monocytogenes antibody through covalent bonding. Enhanced antimicrobial activity of lysozyme-carrying immunonanoparticles was achieved when 0.04 microg/ml anti-L. monocytogenes antibody was used for coating nanoparticles and the resulting immunonanoparticles were then coated with lysozyme for 6 h. Lysozyme-carrying immunonanoparticles with a final concentration of 35 microg/ml reduced L. monocytogenes Scott A populations from ca. 5 log CFU/ml to below the detection limit (< 1 log CFU/ml) within 3 h. However, when 500 microg/ml lysozyme was used, ca. 2 log CFU/ml concentration of L. monocytogenes cells remained culturable after 5 h of treatment. The addition of lysozyme-carrying immunonanoparticles (37 microg/ml) to an L. monocytogenes solution of ca. 7 log CFU/ml for 6 h resulted in 0.9-, 1.0-, and 2.3-log greater reductions of L. monocytogenes cells than that achieved with lysozyme-carrying nanoparticles and lysozyme solutions of 500 and 50 microg/ml, respectively. Overall, lysozyme-carrying immunonanoparticles had significantly more anti-L. monocytogenes activity (P < 0.05) than did lysozyme-carrying nanoparticles and lysozyme solutions at higher concentrations (500 and 50 microg/ml). Our study revealed that the use of lysozyme-carrying immunonanoparticles is more effective than direct addition of lysozyme for inactivating L. monocytogenes in nutrient broth.