Antimicrobial and Cytotoxic Activities of <i>Origanum</i> Essential Oils

TLDR

Gas chromatography–mass spectrometry analysis revealed that the three Origanum essential oils contain high levels of carvacrol, thymol, γ‑terpinene, and p‑cymene, with O. vulgare ssp. hirtum oil being particularly rich in these compounds.

Abstract

Three Origanum essential oils, Origanum vulgare ssp. hirtum, Origanum dictamnus, and a commercially available Origanum oil, were analyzed by gas chromatography−mass spectrometry (GC−MS) and showed a high content of carvacrol, thymol, γ-terpinene, and p-cymene representing 73.7%, 92.8%, and 87.78% of the total oil, respectively. The three essential oils exhibited high levels of antimicrobial activity against eight strains of Gram-positive and Gram-negative bacteria. Among the major components of the three oils, carvacrol and thymol exhibited the highest levels of antimicrobial activity, while their biosynthetic precursors γ-terpinene and p-cymene were inactive. The essential oil of O. vulgare ssp. hirtum was extremely bactericidal at 1/4000 dilution and even at dilutions as high as 1/50000 caused considerable decrease in bacterial growth rates. The same essential oil also exhibited high levels of cytotoxicity against four permanent animal cell lines including two derived from human cancers. Keywords: Origanum vulgare; Origanum dictamus; essential oils; carvacrol; thymol; antimicrobial activity; cytotoxicity; terpenes; cancer