Bioassay-Guided Metabolomic Profiling Reveals Flavanone-Rich Fractions as Antibacterial Agents in Metrodorea nigra

Abstract The increasing prevalence of multidrug-resistant bacteria highlights the urgent need for novel antimicrobial agents from natural sources. This study investigated the antibacterial, antibiofilm, and antioxidant activities of Metrodorea nigra leaves through a bioassay-guided approach combined with UHPLC-MS/MS and feature-based molecular networking (FBMN). The dichloromethane fraction and its subfraction Sp1D exhibited the highest antibacterial activity, with minimum inhibitory concentrations as low as 16–32 µg/ml against Gram-positive strains, including Staphylococcus aureus . Sp1D also demonstrated bactericidal effects and strong inhibition of biofilm formation. Metabolomic analysis revealed a predominance of flavonoids and identified pinostrobin, supported by NMR and MS/MS data, as a major constituent, along with the annotation of rhodomyrtone. FBMN analysis suggested a positive correlation between antibacterial activity and aglycone flavanones, whereas glycosylated flavonoids were mainly associated with inactive samples, indicating the influence of structural features on bioactivity. Antioxidant assays confirmed significant radical scavenging and reducing capacities, particularly for the crude extract and dichloromethane fraction. These findings expand the phytochemical knowledge of M. nigra , including the first report of flavanones in the genus, and highlight its potential as a source of bioactive compounds for the development of new antimicrobial agents.