A new triterpenoid, named alisol Q 23-acetate, as well as fourteen known terpenes, alisol B 23-acetate (2), alisol B (3), alismol (4), 10-O-methyl-alismoxide (5), alismoxide (6), 11-deoxyalisol C (7), 13β,17β-epoxyalisol B 23-acetate (8), 4β,12-dihydroxyguaian-6,10-diene (9), alisol C 23-acetate (10), alisolide (11), 16β-methoxyalisol B monoacetate (12), alisol A (13), 16β-hydroxyalisol B 23-acetate (14), alisol A 24-acetate (15) were isolated from the rhizomes of Alisma orientale. The structures of compounds (1-15) were identified based on 1D and 2D NMR, including (1)H-(1)H COSY, HSQC, HMBC and NOESY spectroscopic analyses. Among these isolates, antibacterial effect of compounds 2, 3, 10, and 15, major constituents of A. orientale was examined. The MIC values of compounds 2, 10, and 15 were 5-10 βg/mL against eight antibiotic resistant strains, which were lower than those from the positive controls (MICs of chloramphenicol and ampicillin were 5-80 μg/mL). Therefore, compounds 2, 10 and 15 exhibited the potent antibacterial activity.

In this study, antibacterial effects of (+)-Medioresinol isolated from stem bark of Sambucus williamsii and its synergistic activities in combination with antibiotics such as ampicillin, cefotaxime, and chloramphenicol were tested by antibacterial susceptibility testing and checkerboard assay. (+)-Medioresinol possessed antibacterial effects against antibiotics-susceptible- or antibiotics-resistant strains. Most of combinations between (+)-Medioresinol and each antibiotic showed synergistic interaction (fractional inhibitory concentration index ≤ 0.5) against bacterial strains including antibiotics-resistant Pseudomonas aeruginosa. Furthermore, the antibiofilm effect of (+)-Medioresinol alone or in combination with each antibiotic was investigated. The results indicated that not only (+)-Medioresinol but also its combination with each antibiotic had antibiofilm activities. It concludes that (+)-Medioresinol has potential as a therapeutic agent and adjuvant for treatment of bacterial infection.