Assessment of antibacterial activity of fractions from burdock leaf against food-related bacteria

The chemical composition and antibacterial activities of burdock leaves fractions against six food-related bacteria (Staphylococcus aureus, Streptococcus pneumoniae, Bacillus subtilis, Escherichia coli, Shigella dysenteriae and Salmonella typhimurium) were first investigated. The burdock leaves extract was fractioned with ethyl acetate, n-butanol and water, named as EF, BF and WF. The data from minimum inhibitory concentration (MIC) values showed that EF and other fractions effectively inhibited the growth of all test bacterial pathogens, the antibacterial activity of EF being much greater than BF and WF. The time–kill study indicated that EF exhibited significant bactericidal activity against all the six pathogens. At 12 h, EF was bactericidal for 4/6, 6/6 and 6/6 strains at 1× MIC, 3× MIC and 5× MIC, respectively. For all the fractions, the antibacterial capacity had a significant correlation with total phenolic content, suggesting that the activities were probably due to the combined action of phenolic compounds. The phenolic compounds of the fractions were then identified for the first time. After activity-guide fractionation and separation by flash chromatogram, two purified active compounds (chlorogenic acid, rutin) were obtained, and identified by UPLC–MS/MS. The ethyl acetate fraction based on its lower MIC values, concentration and time-dependent antibacterial and bactericidal activities could be useful in control of foodborne bacterial pathogens.