Xanthomonas campestris pv. vesicatoria (Xcv) causes brown spots on the leaves, stems, and fruits of plants, called bacterial leaf scorch (BLS). For the control of pathogens, antibiotics have been used frequently, and they can develop the resistance. In this study, the bactericidal and synergistic effects of caraway oil and its main components against the pathogen (Xcv) were investigated. The tested caraway oil consisted of 58.4% of carvone and 31.1% of limonene. The minimum inhibitory concentration (MIC) of caraway oil and carvone was the same as 125 μg mL−1, and the minimum bactericidal concentration (MBC) was 1000 μg mL−1 for caraway oil and 500 μg mL−1 for carvone, while limonene showed no inhibition below 1000 μg ml−1. In the growth of Xcv, carvone treatment over 31.3 μg mL−1 inhibited dose-dependently, and the bactericidal effect showed after 18 h more than 250 μg mL−1; It was agreed with the release of intracellular components over 250 μg mL−1, especially. Furthermore, carvone damaged the plasmid DNA of Xcv, and it would be the reason for the bactericidal activity. The synergistic effect of carvone was found with β-lactams selectively; the fractional inhibitory concentration (FIC) indexes of carvone with ampicillin or amoxicillin were below 0.5, and the mixture of carvone (125 μg mL−1) and ampicillin (500 μg mL−1) showed the bactericidal activity as well.
Dendranthema zawadskii is a one of the popular plants as native in South Korea. In this study, linarin was isolated and purified using silica-gel, Diaion, and Sephadex LH-20 from the aerial parts of D. zawadskii. The chemical structure was completely identified through spectroscopic data including 1D, 2D nucleic magnetic resonance, and HRFABMS. Furthermore, linarin inhibited the bacterial neuraminidase (BNA) activity with 13.5 μM of IC 50 dose-dependently. Through the enzyme kinetic experiments, linarin as BNA inhibitor exhibited a typical noncompetitive inhibition mode which K m was contestant and V max decreased as the concentration of the inhibitor increased. It was further identified that the inhibition constant was 16.0 μM. Linarin was the most abundance metabolite in the aerial part of D. zawadskii extract by UHPLC-TOF/MS analysis. Therefore, D. zawadskii and its main component are expected that it can be effectively used for the infection and inflammation caused by bacteria.
This study aimed to isolate bacterial neuraminidase (BNA) inhibitory O-methylated quercetin derivatives from the aerial parts of S. pubescens. All the isolated compounds were identified as O-methylated quercetin (1–4), which were exhibited to be noncompetitive inhibitors against BNA, with IC50 ranging from 14.0 to 84.1 μM. The responsible compounds (1–4) showed a significant correlation between BNA inhibitory effects and the number of O-methyl groups on quercetin; mono (1, IC50 = 14.0 μM) > di (2 and 3, IC50 = 24.3 and 25.8 μM) > tri (4, IC50 = 84.1 μM). In addition, the binding affinities between BNA and inhibitors (1–4) were also examined by fluorescence quenching effect with the related constants (KSV, KA, and n). The most active inhibitor 1 possessed a KSV with 0.0252 × 105 L mol−1. Furthermore, the relative distribution of BNA inhibitory O-methylated quercetins (1–4) in S. pubescens extract was evaluated using LC-Q-TOF/MS analysis.
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