Utilization of plant by-products contributes to the efficient use of natural resources and expands the range of bioactive materials of botanical origin. Oregano (Origanum vulgare L.) is widely recognized for its active metabolites; however, its underground parts have received little attention. In this study, 14 phenolic compounds were identified in water extracts of oregano leaves (OVL) and rhizomes (OVR) using LC-MS/MS-DAD. Both extracts contained rosmarinic acid, oreganol C, and caffeic acid, while OVL also included oreganol A, oreganol B, and luteolin-7-O-diglucuronide. Remarkably, OVR was revealed as a previously unreported natural source of salvianolic acid A. The antioxidant potential, evaluated by DPPH, ABTS, and H2O2 scavenging assays, demonstrated comparable activities of OVL and OVR. Antimicrobial testing (broth microdilution and isothermal microcalorimetry) confirmed inhibitory effects against Staphylococcus aureus (MSSA, MRSA), Proteus mirabilis, and Enterococcus faecalis. Notably, OVR showed stronger inhibition of staphylococcal metabolic activity (≥ 0.75 mg/mL) than OVL (≥ 5.0 mg/mL). Cytotoxicity assessed by MTT assay on HaCaT keratinocytes indicated no significant reduction in cell viability at concentrations ≤ 100 μg/mL, supporting the biocompatibility of both extracts. The rhizome extract further showed a safety profile comparable to that of the leaf extract, supporting its potential for further biomedical use. The present study demonstrates that oregano rhizomes represent an unexplored botanical source of antioxidant and anti-staphylococcal compounds, expanding current knowledge on the phytochemical potential of this species.

Department of Cell and Molecular Biology of Drugs Faculty of Pharmacy Comenius University in Bratislava Bratislava Slovakia

Department of Pharmacognosy and Botany Faculty of Pharmacy Comenius University Bratislava Bratislava Slovakia

Department of Pharmacology Faculty of Medicine Pavol Jozef Šafárik University in Košice Košice Slovakia

Institute of Microbiology Faculty of Medicine Comenius University Bratislava and the University Hospital in Bratislava Bratislava Slovakia

National Agricultural and Food Centre Research Institute of Plant Production Piešťany Slovakia

Prague Burn Centre 3rd Faculty of Medicine and University Hospital Královské Vinohrady Prague Czech Republic

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