Screening and identification of the antibacterial bioactive compounds from Lonicera japonica Thunb. leaves

Our aim was to screen for antibacterial bioactive compounds from Lonicera japonica leaves. Staphylococcus aureus and Escherichia coli were used as the indicator bacteria. Bacteriostatic assay-guided extraction and stepwise partitioning of the samples yielded five compounds of interest. Antimicrobial activities of the compounds were determined using a disk diffusion assay. Extracts, fractions, and compounds from L. japonica leaves possessed considerable antibacterial activities against the tested bacterial strains and the most active fraction was attributed to J3B2, which primarily contained 3,5-di-O-caffeoylquinic acid and 4,5-di-O-caffeoylquinic acid. Meanwhile, five bacteriostatic constituents were isolated (3-O-caffeoylquinic acid, secoxyloganin, luteoloside, 3,5-di-O-caffeoylquinic acid and 4,5-di-O-caffeoylquinic acid), among which, secoxyloganin was isolated for the first time from leaves. The antibacterial activity of the compounds was in the order of 3,5-bis-O-caffeoyl quinic acid, 4,5-bis-O-caffeoylquinic acid, luteoloside > 3-O-caffeoylquinic acid > secoxyloganin. Our results suggested that the phenolic compounds might significantly contribute to antibacterial activity and were the most responsible for the bacteriostatic activity of L. japonica leaves.