Comparative Secondary Metabolite Analysis and Antimicrobial Assessment of Agastache foeniculum (Pursh) Kuntze Leaf and Flower Extracts

Agastache foeniculum (Pursh) Kuntze, a member of the Lamiaceae family, is a phytochemically rich yet underexplored species with potential biomedical applications. This study aimed to provide an organ-specific chemical characterization of its secondary metabolites and to evaluate the antimicrobial potential of ethanolic extracts derived separately from its leaves and flowers. Using UHPLC-MS/MS, we identified a total of 54 compounds, including phenolic acids and flavonoids. In total, 35 compounds in the flower extract and 38 in the leaf extract were reported here for the first time. The antimicrobial activity of both extracts was tested against six multidrug-resistant (MDR) clinical bacterial isolates (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Citrobacter freundii, Achromobacter xylosoxidans, and Acinetobacter baumannii) using seven concentration levels (12.5–87.5%). While the leaf extract showed limited antibacterial effects, the flower extract demonstrated stronger, concentration-dependent inhibitory effects. At concentrations of 62.5% and above, it markedly reduced viable bacterial counts in all tested MDR strains. These findings highlight the importance of organ-specific phytochemical analysis in medicinal plants and suggest that A. foeniculum, particularly its flowers, may serve as a promising source of bioactive compounds for further antimicrobial research and development.