Synergistic inhibition of Listeria monocytogenes biofilms by Nisin and Licochalcone A

This study evaluated the synergistic antibacterial and antibiofilm effects of Nisin and Licochalcone A (LCA) against Listeria monocytogenes ATCC 19114 and CMCC 8605. Minimum inhibitory concentration (MIC) and fractional inhibitory concentration index (FICI) were determined, along with biofilm quantification, microscopic observations, gene expression analysis, and an application test on cantaloupe peel. The combination showed strong synergy, with FICI values of 0.375 for both strains, and significantly inhibited bacterial growth. Meanwhile, the combined treatment successfully inhibited biofilm formation and eradicated existing biofilms, as verified through crystal violet staining. Scanning electron microscopy and confocal scanning laser microscopy enabled visualization of the destruction of established L. monocytogenes biofilms by Nisin and LCA individually or combined. The combined treatment significantly reduced cell membrane integrity, biofilm metabolic activity, and EPS production ( P < 0.05). Furthermore, it modulated the expression of genes related to flagella, quorum sensing, EPS synthesis, and virulence. Practical application showed that Nisin + LCA significantly decreased biofilm on cantaloupe peel. To summarize, the combination of Nisin and LCA demonstrated great potential for reducing and controlling the L. monocytogenes contamination within the food industry. • Nisin + LCA showed a synergistic antibacterial effect on L. monocytogenes. • Combined treatment inhibited biofilm formation by L. monocytogenes. • Combined treatment efficiently enhanced the removal of the EPS in the biofilms. • Combined treatment regulated the expression of genes in L. monocytogenes.