Bioactive potential of <i>Origanum heracleoticum</i> L. essential oil: Chemical composition and its antimicrobial and anticancer properties

Oregano (Origanum heracleoticum L.) is a widely consumed aromatic spice, recognized as a medicinal plant due to its diverse biological and pharmaceutical properties. Essential oils (EOs) exhibit remarkable biological activities, primarily attributed to their high concentrations of volatile aromatic compounds. This study aimed to determine the chemical composition of Bulgarian oregano essential oil (OEO) and evaluate its biological activities, including anticancer, antimicrobial, anti-biofilm, and anti-quorum sensing properties. Chemical analysis revealed that carvacrol (76.90%) and p-cymene (12.84%) were the predominant components of OEO. The MTT assay demonstrated that OEO significantly reduced the viability of human lung adenocarcinoma epithelial cells (A549), human hepatocellular carcinoma cells (HepG2), and human breast adenocarcinoma cells (MDA-MB-231) at all tested concentrations (3.9-1000 μg/mL), while exhibiting considerably lower toxicity towards healthy mouse fibroblast cells (L929). Among the tested cancer cell lines, A549 cells were the most sensitive to OEO, with IC50 values indicating greater cytotoxicity towards A549 and MDA-MB-231 cells at lower concentrations. The antimicrobial, anti-biofilm, and anti-quorum sensing (anti-violacein) activities of OEO were assessed against Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa PA01, P. aeruginosa ATCC 27853, Candida albicans ATCC 10231, and Chromobacterium violaceum ATCC 12472. The results revealed that OEO exhibits potent antimicrobial and anti-biofilm activities against a range of microorganisms.