Antimicrobial activities of various essential oils and their main aromatic volatile constituents

In continuation of our effort on data correlation of antimicrobial activities of aroma compounds among various essential oils and plant extracts [1], the aromatic volatiles p-cymene, carvacrol, eugenol and thymol as well as the essential oils of Cinnamomum zeylanicum, Eugenia caryophyllus, Origanum vulgare, Pimenta dioica, Pimenta racemosa, Satureja hortensis, Trachyspermum ammi and Thymus vulgaris were investigated. Therefore, these samples and as reference substances synthetic antibiotics as well as the natural antimicrobial components carveol, m-cresol, o-cresol and p-cresol were tested against strains of two Gram-(+) and five Gram-(-) bacteria and the fungus Candida albicans using agar dilution and agar diffusion methods. The analysis of the chemical composition of the essential oils by means of GC and GC-MS focusing on aromatic volatiles resulted as follows: C. zeylanicum: eugenol (74.9%); E. caryophyllus: eugenol (76.8%); O. vulgare: carvacrol (66.1%); p-cymene (9.2%); P. dioica: eugenol (76.0%); P. racemosa: eugenol (45.6%); S. hortensis: carvacrol (41.5%), p-cymene (10.7%), thymol (8.7%); T. ammi: thymol (43.7%), p-cymene (17.7%); T. vulgare: thymol (43.4%), p-cymene (23.5%) and carvacrol (4.1%). All investigated aromatic volatiles and essential oils exhibited a medium to strong antimicrobial activity against the Gram-(+) bacteria Staphylococcus aureus and Enterococcus faecalis and the Gram-(-) bacteria Escherichia coli, Klebsiella pneumoniae, Proteus vulgaris, Pseudomonas aeruginosa and Salmonella sp., whereas merely weak to medium effects were observed against Candida albicans.

References: [1] Jirovetz, L. et al. (2006) Recent Progress in Medicinal Plants, Vol. 13: Search for Natural Drugs (Govil, J.N., Singh, V.K., Arunachalam, C., eds.), Studium Press LLC, Houston (Tx), USA.