Action of lysozyme and nisin mixtures against lactic acid bacteria

Lysozyme was formulated together with nisin for usage against food spoilage lactobacilli. The mixtures demonstrated improved minimal inhibitory concen trations (MIC), compared to the parent compounds, for many of the bacteria and media tested, including high salt media in which lysozyme lost virtuall y all of its activity. Synergy was also observed through measurement of the kinetics of bacterial killing of L. curvatus 845, in which strain synergy had been observed in MIC assays. The combination of lysozyme and nisin caus ed more severe cell damage as viewed by scanning electron microscopy, and a consequent change in optical density at 600 nm, compared to the parent com pounds, effects that were presumed to reflect the action of lysozyme. In ad dition, the combination caused more rapid permeabilization (depolarization) of the cytoplasmic membranes of Staphylococcus aureus, an effect that refl ected the mechanism of action of nisin. Thus, nisin and lysozyme appear to demonstrate synergy against gram-positive bacteria because they reinforce e ach others mechanisms of bacterial killing. (C) 2000 Elsevier Science B.V. All rights reserved.