Correlation of Antimicrobial Activities of Various Essential Oils and Their Main Aromatic Volatile Constituents

The pure aromatic volatiles p-cymene, carvacrol, eugenol and thymol as well as commercial essential oils of Cinnamomum zeylanicum, Origanum vulgare, Pimenta dioica, Pimenta racemosa, Satureja hortensis, Syzygium aromaticum, Thymus vulgaris and Trachyspermum ammi were investigated concerning antimicrobial activities. Therefore, these samples and, as reference Substances, synthetic antibiotics and the natural antimicrobial components carveol, m, o- and p-cresol were tested against strains of two Gram-positive and five Gram-negative bacteria and the yeast Candida albicans using agar dilution and agar diffusion methods. The analysis of the chemical composition of the essential oils by means of GC and GUMS focusing on aromatic volatiles produced the following results: C. zeylanicum: eugenol (74.9%); O. vulgare: carvacrol (66.1%) and p-cymene (9.2%); P dioica: eugenol (76.0%); P. racemosa: eugenol (45.6%); S. hortensis: carvacrol (41.5%), p-cymene (10.7%) and thymol (8.7%); S. aromaticum: eugenol (76.8%); T vulgaris: thymol (43.4%), p-cymene (23.5%) and carvacrol (4.1%); T. ammi: thymol (43.7%) and p-cymene (17.7%). All investigated aromatic volatiles and essential oils exhibited strong effects against the yeast Candida albicans and medium to strong antimicrobial activity against the Gram-positive bacteria Staphylococcus aureus and Enterococcus faecalis and the Gram-negative bacteria Escherichia coli, Klebsiella pneumoniae, Proteus vulgaris, and Salmonella sp., whereas weaker effects were observed against Pseudomonas aeruginosa.