Inhibitory effect of licochalcone A on dual-species biofilms of Listeria monocytogenes and Staphylococcus aureus: mechanism involved in quorum sensing and application in beef

This study aimed to investigate the antibiofilm activity and mechanism of licochalcone A (Lico A), a natural flavonoid compound, against biofilms of L. monocytogenes, S. aureus, and their dual-species, and evaluate the potential application of Lico A in beef. The minimum inhibitory concentration (MIC) of Lico A against both L. monocytogenes and S. aureus was 7.5 μg/mL. Crystal violet staining and confocal laser scanning microscopic analysis showed that Sub-MICs of Lico A remarkably inhibited the biofilm formation of mono- and dual-species of L. monocytogenes and S. aureus. Meanwhile, Lico A significantly reduced the extracellular polymeric substances (EPS) production and the metabolic activity of biofilms, causing decreases in surface hydrophobicity, auto-aggregation, and motility. Furthermore, Lico A inhibited autoinducer-2 signaling activity by binding to LuxS and suppressing luxS expression, which disturbed the interspecies communication and thereby impeded biofilm formation. Biofilm-related genes such as sigB, flaA, icaA, and SarA were also regulated by Lico A. Importantly, Lico A effectively inhibited the dual-species biofilms of S. aureus and L. monocytogenes on beef, decreasing by 1.1 and 1.0 log CFU/g, respectively, on day 7 of storage at 4 °C. These findings highlight the potential of Lico A as a natural antibiofilm agent, especially against mixed-species biofilms, in food industry applications.