Assessment of the Antimicrobial, Antioxidant, and Antiproliferative Potential of Sideritis raeseri subps. raeseri Essential Oil

The aim of the present study was to investigate the antimicrobial potential of Sideritis raeseri subps. raeseri essential oil (EO) against common food spoilage and pathogenic microorganisms and evaluate its antioxidant and antiproliferative activity. The EO was isolated by steam distillation and analyzed by GC/MS. The main constituents identified were geranyl-p-cymene (25.08%), geranyl-γ-terpinene (15.17%), and geranyl-linalool (14.04%). Initially, its activity against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Listeria monocytogenes, Salmonella Enteritidis, Salmonella Typhimurium, Pseudomonas fragi, Saccharomyces cerevisiae, and Aspergillus niger was screened by the disk diffusion method. Subsequently, minimum inhibitory concentration (MIC), non-inhibitory concentration (NIC), and minimum lethal concentration (MLC) values were determined. Growth inhibition of all microorganisms tested was documented, although it was significantly lower compared to gentamycin, ciproxin, and voriconazole, which were used as positive controls. In a next step, its direct antioxidant properties were examined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays, and the IC₅₀ values were determined. The potential cytoprotective activity of the oil against H₂O₂-induced oxidative stress and DNA damage was studied in human immortalized keratinocyte (HaCaT) cells using the comet assay. Finally, the antiproliferative activity of the oil was evaluated against a panel of cancer cell lines including A375, Caco2, PC3, and DU145 and the non-cancerous HaCaT cell line using the sulforhodamine B (SRB) assay, and the EC₅₀ values were determined. The oil demonstrated weak radical scavenging activity, noteworthy cytoprotective activity against H₂O₂-induced oxidative stress and DNA damage in HaCaT cells, and antiproliferative activity against all cell lines tested, being more sensitive against the in vitro model of skin melanoma.

Keywords: Sideritis raeseri subsp. raeseri; antimicrobial; antioxidant; antiproliferative activity; essential oil.