Antibacterial compounds against fish pathogenic bacteria from a combined extract of Angelica gigas and Artemisia iwayomogi and their quantitative analyses

In the search for antibiotic alternatives from safe and effective medicinal plants against fish pathogenic bacteria, we found that a combined extract (CE) of 1:1 (w/w) ratio of Angelica gigas Nakai roots and aerial parts of Artemisia iwayomogi Kitamura showed antibacterial activity against the fish pathogenic bacteria. By antibacterial activity-guided fractionations and isolations, five compounds were isolated and identified as decursinol angelate (1), decursin (2), xanthotoxin (3), demethylsuberosin (4), and 2,4-dihydroxy-6-methoxyacetophenone (5) through spectroscopic analyses, such as nuclear magnetic resonance (NMR) and mass spectrometry (MS). Among the compounds, 1 and 2 showed the highest antibacterial activities against Streptococcus iniae and Vibrio anguillarum, showing minimum inhibitory concentrations (MICs) of 62.5–250 μg/mL. Compounds 3, 4, and 5 were also found to be active, with MICs of 31.25–1,000 μg/mL for those strains. Furthermore, active compounds, 1 and 2 in CE were simultaneously quantified using high-performance liquid chromatography-tandem MS (HPLC-MS/MS). The average contents of 1 and 2 in CE was 3.68% and 6.14%, respectively. The established method showed reliable linearity (r > 0.99), good precision, accuracy, and specificity with intraand inter-day variations of < 2 % and recoveries of 90.13%–108.57%. These results may be helpful for establishing the chemical profile of CE for its commercialization as an antibiotic alternative in aquaculture.