Inhibitory mechanism of Salmonella Derby biofilm formation by sub-inhibitory concentrations of clove and oregano essential oil: A global transcriptomic study

The present study aimed to investigate the inhibition of clove essential oil (CEO) and oregano essential oil (OEO) on Salmonella Derby biofilm formation and explore the molecular mechanisms involved in the effects of CEO and OEO by using the transcriptomic approach. The results showed that CEO and OEO significantly inhibited the biofilm formation of S. Derby at both 1/2 and 1/4 MICs, and there was no significant difference in biofilm inhibition between the two sub-MICs. The transcriptomic analysis revealed that 1/4 MIC CEO and OEO (0.2 mg/mL and 0.05 mg/mL) significantly altered gene expression in S. Derby biofilm. Compared with the untreated biofilms, there were 392 differentially expressed genes (DEGs) were up-regulated and 373 DEGs were down-regulated in CEO treatment group, while 679 up-regulated and 709 down-regulated DEGs in OEO treatment group. Interestingly, enrichment analysis of the DEGs showed that both CEO and OEO significantly down-regulated the energy metabolism-related genes and these DEGs were mainly involved in pathways of fatty acid degradation, TCA cycle, and oxidative phosphorylation. This finding was confirmed in subsequent ATP content, ATPase activity and NADH oxidase activity assays. Moreover, compared to OEO treatment, CEO treatment also down-regulated DEGs enriched in ribosome and arginine, lysine, phenylalanine, tyrosine, and tryptophan biosynthesis pathways. This study reveals the biofilm inhibitory effects and mechanisms of CEO and OEO against S. Derby at sub-MICs, which may provide theoretical support for preventing biofilms of foodborne pathogens in the food industry.