Antimicrobial properties of lysozyme in relation to foodborne vegetative bacteria

The purpose of this review is to describe the antibacterial properties and mode of action of lysozyme against gram-positive and gram-negative bacteria, and to provide insight in the underlying causes of bacterial resistance or sensitivity to lysozyme. Such insight improves our understanding of the role of this ubiquitous enzyme in antibacterial defense strategies in nature and provides a basis for the development and improvement of applications of this enzyme as an antibacterial agent. The bactericidal properties of lysozyme are primarily ascribed to its N-acetylmuramoylhydrolase enzymic activity, resulting in peptidoglycan hydrolysis and cell lysis. However, an increasing body of evidence supports the existence of a nonenzymic and/or nonlytic mode of action. Because gram-negative bacteria, including some major foodborne pathogens, are normally insensitive to lysozyme by virtue of their outer membrane that acts as a physical barrier preventing access of the enzyme, several strategies have been developed to extend the working spectrum of lysozyme to gram-negative bacteria. These include denaturation of lysozyme, modification of lysozyme by covalent attachment of polysaccharides, fatty acids and other compounds, attachment of C-terminal hydrophobic peptides to lysozyme by genetic modification, and the use of outer membrane permeabilizing agents such as EDTA or polycations or permeabilizing treatments such as high hydrostatic pressure treatment.