Purpose: To determine the chemical composition and anti-biofilm activity of burdock leaf fractions against Staphylococcus aureus

Methods: The anti-biofilm activity of burdock leaf fractions obtained by column chromatography against S. aureus was determined by minimum inhibitory concentration (MIC). Scanning electron microscopy was employed to further investigate the inhibitory activity. Analysis of the chemical composition of the fractions was performed by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS).

Results: The 20 and 34 % ethanol fractions each inhibited the formation of biofilm by S. aureus, with half maximal inhibitory concentration (IC₅₀) ranging from 110 to 150 μg/ml. The 70 % ethanol elution fraction exhibited the strongest inhibitory activity against biofilm formation with IC₅₀ of 13 μg/ml. The minimum inhibitory concentration of the 70 % ethanol fraction completely inhibited the formation of biofilm at a concentration of 0.5 mg/ml, which was lower than the MIC for the growth of the test bacterium (1.25 mg/ml). Scanning electron microscopy (SEM) showed that there was no biofilm formation for cultures treated with burdock leaf fraction, thus confirming the inhibitory efficiency of burdock leaf fraction against biofilm formation. UPLC-MS data identified five active compounds, namely, :caffeic acid, p-coumaric acid, cynarin, quercetin and luteolin.

Conclusion: The biofilm formation inhibitory effect of burdock leaf was not only due to its inhibitory effect on bacterial growth but appear to be influenced by its effect on bacterial surface hydrophobicity, and aggregation. Thus, the leaf fractions may be useful in the control of biofilms.