Effect of ethanol fraction of burdock leaf on biofilm formation and bacteria growth

The inhibition effects of burdock leaf ethanol fraction on the viability, biofilm formation of food-related bacteria and the mechanism were first investigated. The results showed that burdock leaf ethanol fraction significantly inhibited the formation of biofilm by Staphylococcus aureus and Listeria monocytogenes. The lowest concentration of the fraction that showed 100 % inhibition on the formation of L. monocytogenes biofilm was 2.50 mg/ml, which was equal to the minimum inhibitory concentration (MIC) against bacterial growth. As for S. aureus, the lowest concentration of burdock leaf fraction that completely inhibited (100 %) the formation of biofilm was found to be 1.25 mg/ml, which was lower than MIC of the fraction (2.5 mg/ml). Thus, the biofilm inhibition effect of burdock leaf fraction against S. aureus was not completely due to the inhibition on bacteria growth. Then, the effects of burdock leaf fraction on quorum sensing signals were evaluated through GC–MS/MS analysis. The results indicated that burdock leaf fraction interfered with quorum sensing system and changed the composition of signaling molecules, thereby affecting the function of the quorum sensing system, significantly inhibiting the formation of biofilm. Then, the chemical composition of burdock leaf fraction was analyzed by ultra performance liquid chromatography (UPLC)–MS/MS and eight active compounds were identified. The burdock leaf fraction based on its interfering with quorum sensing systems and the significant inhibition on the formation of biofilm could be highly useful in control of biofilms.