Deciphering the inhibitory mechanisms of cinnamaldehyde on biofilm formation of Listeria monocytogenes and implement these strategies to control its transfer to beef surfaces

Abstract

Natural essential oils have received widespread attention as promising microbial inhibitors, whereas a comprehensive understanding of their mechanisms underlying biofilm control and impact on biofilm cross-contamination on meat remains poorly understood. In this study, Listeria monocytogenes (Lm) biofilms were treated with sub-inhibitory concentrations of cinnamaldehyde (CA) and characterized over a 4-day period. Both 1/2 MIC (160 μg/mL) and 1/4 MIC (80 μg/mL) CA delayed the development of Lm biofilm on abiotic surfaces and reduced the maximum biofilm formation. The limited effect of 1/4 MIC CA on the flagellar-mediated motility of Lm during initial adhesion indicated that hindering bacterial motility was not the main reason for CA inhibition of biofilm formation. Transcriptomics results showed that CA was involved in inhibitory pathways dominated by energy metabolism and peptidoglycan synthesis during the initial adhesion period and the maturation period of the biofilm, respectively. This posed an obstacle to the polymers required for biofilm cell adhesion and the energy consumption required for their production. Down-regulation of genes associated with multiple signalling systems and virulence factors also suggested that CA further mitigated resistance and virulence in residual biofilm cells. In addition, quantification of biofilm cells transferred to beef surfaces confirmed that CA significantly reduces the biomass transferred and the risk of persistent biofilm contamination. This study provided the theoretical basis for the control of Lm biofilm and its cross-contamination in the food industry by natural essential oils.