Synergistic Antimicrobial Activity between Light or Thermal Treatments and Lauric Arginate: Membrane Damage and Oxidative Stress

The need for more effective antimicrobials is critical for the food industry to improve food safety and reduce spoilage of minimally processed foods. The current study was initiated to develop an efficient and novel antimicrobial approach which combines physical treatments (UV-A or mild heat) and generally recognized as safe lauroyl arginate ethyl (LAE) to inactivate surrogate strains including Escherichia coli and Listeria innocua . Synergistic inactivation of bacteria resulted in about 6 log reduction of target bacteria while individual treatments resulted in less than 1.5 log inactivation under the same set of conditions. In addition, synergistic mechanism between LAE and UV-A/mild heat was evaluated by supplementing with a variety of antioxidants for suppressing oxidative stress and measurement of cell membrane damage by nucleic acid release. These results demonstrate that synergistic antimicrobial activity of LAE and mild physical stresses was suppressed by supplementation with antioxidants. The research also compared LAE with another membrane targeting lipopeptide antimicrobial agent, polymyxin B, to understand the uniqueness of LAE induced synergy. Briefly, differences in modes of action between LAE and polymyxin B were characterized by comparing minimum inhibitory concentration, damage to liposomes and oxidative stress generation. These differences in the mode of action between LAE and polymyxin B suggested that both compounds target cell membrane but significantly differ in mechanisms including membrane disruption and oxidative stress generation. Overall, this study illustrates synergistic antimicrobial activity of LAE with light or mild heat and indicates novel oxidative stress pathway that enhances the activity of LAE beyond membrane damage. Significance and Impact of Study This work highlights an effective antimicrobial processing approach between novel combination of lauroyl arginate ethyl (LAE) and two different physical treatments, light (UV-A) and mild heat. Both combinations demonstrated synergistic inactivation against model Gram-negative bacterium or Gram-positive bacterium or both by more than 5-log reduction. Further mechanistic study revealed that oxidative stress is responsible for synergistic inactivation between LAE and UV-A; while both membrane damage and oxidative stress are responsible for synergistic combination between LAE and mild heat. Mode of action of LAE was further compared with polymyxin B and analyzed using artificial membrane model systems and addition of antioxidants. The proposed combination of LAE and common physical treatments may improve food preservation, food safety and current sanitation process for the food industry and inactivation of pathogenic strains in biomedical environments.