Antimicrobial and cytotoxic activities of Origanum essential oils

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, gamma-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 gamma-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.