The anti-biofilm and anti-virulence mechanisms of carvacrol against Listeria monocytogenes and the application in food systems

The virulence factors including biofilm and virulence proteins in Listeria monocytogenes ( L. monocytogenes ) threatens human health. Herein, the inhibitory mechanisms of carvacrol (CAR) on the biofilm formation and virulence production in L. monocytogenes were explored. It was found the minimum biofilm inhibition concentration of CAR was 0.8 mg/mL. CAR could effectively inhibit bacterial biofilm formation by reduction of extracellular polymeric substance, including extracellular polysaccharides, proteins, and DNA. CAR could interfere with the bacterial swarming and swimming motilities, thereby hindering biofilm development. Hemolytic capability of Listeriolysin O was significantly decreased from 85.75 % to 28.13 % after treatment with CAR at the minimum inhibitory concentration (MIC). Transcriptomic analysis revealed exposure to 1/2 MIC of CAR resulted in 969 differentially expressed genes, with downregulation of virulence factor-related genes. CAR might bind to AgrB within the quorum sensing system, thereby affecting the biofilm formation regulation and virulence expression. In addition, CAR exhibited efficient inhibitory effects on the biofilm formation on different food contacting materials and vegetable surfaces. These findings provided new insights into biofilm-inhibition and virulence-reduction mechanisms of CAR on L. monocytogenes, suggesting potential applications in controlling L. monocytogenes biofilm contamination in food industries.