Correlation between phenological changes, chemical composition and biological activities of the essential oil from Moroccan endemic Oregano (Origanum compactum Benth)

The aims of this study were to evaluate the chemical composition, antibacterial, antioxidant and antileishmanial activities of essential oils extracted by hydrodistillation from the aerial parts of wild endemic Moroccan Origanum compactum at three phenological stages (vegetative, flowering and post-flowering). GC/MS analyses of the essential oils have revealed the presence of 37 components represented mainly by oxygenated monoterpenes (49.4–62.975%) and hydrocarbons monoterpenes (31.815–43.632%). Carvacrol, thymol, p-cymene and γ-terpinene were the major components of essential oils at three phenological stages. The antioxidant activity was estimated by DPPH free radical scavenging ability and reducing power. Essential oils obtained from post-flowering stage showed the highest antioxidant capacity with IC50 values of 172.87 ± 5.38 μg/mL and IC50 = 53.28 ± 2.64 μg/mL revealed by the DPPH and reducing power assay respectively. The antibacterial activity was tested against pathogenic strains using the diffusion method, the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) by microtitration assay. The essential oil of vegetative and flowering stage showed remarkable antibacterial activities against Proteus mirabilis with an inhibition diameter of 43 ± 2.12 and 47 ± 2.73 mm respectively. Moreover, the best bactericidal action was revealed by the essential oil of flowering stage against S. aureus MBLA (MIC = MBC = 0.0312% (v/v)). The antiparasitic activity was tested against Leishmania major, Leishmania tropica and Leishmania infantum using MTT (3- (4.5-dimethylthiazol- 2yl) −2.5-diphenyltetrazolium bromide) assay. All essential oils showed remarkable cytotoxic activities against tested Leishmania species compared with Glucantime. The essential oil extracted at the flowering stage revealed the best antileishmanial activity. The leishmanicidal effect displayed against L. infantum was recorded at the low concentration with IC50 = 0.02 ± 0.004 μg/mL. The findings highlighted in this study show that flowering stage is the best optimal harvesting times of Origanum compactum for food and pharmaceutical applications.