Abstract
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 (IC 50 ) ranging from 110 to 150 μg/ml. The 70 % ethanol elution fraction exhibited the strongest inhibitory activity against biofilm formation with IC 50 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. Keywords : Biofilm, Staphylococcus aureus, Arctium lappa , Burdock leaf, Scanning electron microscope, Ultra-performance liquid chromatography-mass spectrometry
Highlights
Biofilm is a stubborn contamination source in food industry sectors such as dairy processing, fresh agricultural product, poultry processing and red meat processing [1]
The 70 % ethanol elution fraction exhibited the strongest inhibitory activity on biofilm formation with an IC50 of 13 μg/ml, while water elution fraction showed no significant inhibition on the formation of bacterial biofilms at the concentration of 5 mg/ml
The inhibitory effect of the fraction against biofilm formation was related to the concentration
Summary
Biofilm is a stubborn contamination source in food industry sectors such as dairy processing, fresh agricultural product, poultry processing and red meat processing [1]. A food-related bacterium S. aureus was chosen as the test microbe against which, the inhibitory activity of burdock leaf extract assessed for formation of biofilm. Visual analysis by scanning electron microscopy (SEM) was performed to further evaluate the effect of burdock leaf fractions on biofilm formation. Measurement of the effect of burdock leaf fractions on formation of biofilm by S. aureus. The bacterial suspension (108 CFU/ml, 1.0 ml) was transferred into 9.0 ml of fresh broth (trypsin: 10g/L, yeast extract: 5g/L, NaCl: 5g/L) containing various concentrations of burdock leaf fractions dissolved in alcohol and sterilized. A scanning electron microscopy analysis [15] was used to further observe the inhibitory activity of 70 % ethanol elution fraction against the formation of biofilm by S. aureus on plastic coverslips. P < 0.05 was considered to indicate statistical significance
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