Inhibitory effects of clove and oregano essential oils on biofilm formation of Salmonella Derby isolated from beef processing plant

The biofilm of Salmonella is a major source of meat contamination and disease transmission. This study aimed to investigate biofilm inhibitory effects and mechanisms of clove essential oil (CEO) and oregano essential oil (OEO) at different concentrations on Salmonella Derby (S. Derby). Crystal violet staining assay was employed to investigate the anti-biofilm effects of the essential oils (EOs), and the initial adhesion, bacterial metabolism, extracellular polymer (EPS) and microscopic examination were used to explore the inhibition mechanism. The results showed that EOs at minimum inhibitory concentrations (MIC) significantly inhibited the biofilm formation of S. Derby. At 1/8 MIC, the two EOs had no significant inhibitory effect on the growth of S. Derby planktonic bacteria, but the biofilm inhibition rates of CEO and OEO were 90.29% and 48.79%, respectively. Scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM) analysis also confirmed distinguishable anti-biofilm effects of CEO and OEO. In addition, our results showed that CEO and OEO inhibited S. Derby biofilm formation by inhibiting metabolic activity and EPS production. This work provides a theoretical basis for the future mechanism research of EOs in the control of biofilm formation of S. Derby and supports the potential application of CEO and OEO in the food industry.