Comparative evaluation of the antimicrobial activity of 19 essential oils

In our research on natural compounds efficient against human pathogen or opportunist microorganisms contracted by food or water, the antimicrobial activity of 19 essential oils (EOs) was investigated against 11 bacterial species (6 Gram positive, 5 Gram negative) and 7 fungal species (2 dermatophytes, 1 mould, 4 yeasts) using microdilution assays. Five essential oils were obtained from Tunisian plants (EOtun): Artemisia herba-alba Asso, Juniperus phoenicea L., Rosmarinus officinalis L., Ruta graveolens L. and Thymus vulgaris L., whereas others were commercial products (EOcom). Overall, T. vulgaris EOtun was the most efficient EO against both bacteria (Gram negative: MIC ≤ 0.34 mg/mL; Gram positive: MIC ≤ 0.70 mg/mL) and fungi (yeasts: MIC ≤ 0.55 mg/mL; mould: MIC = 0.30 mg/mL; dermatophytes: MIC ≤ 0.07 mg/mL). Two EOcom displayed both acceptable antibacterial and antifungal potency, although weaker than T. vulgaris EOtun activity: Origanum vulgare EOcom (bacteria: MIC ≤ 1.13 mg/mL, fungi: MIC ≤ 1.80 mg/mL), and Cymbopogon martinii var. motia EOcom (bacteria: MIC ≤ 1.00 mg/mL, fungi: MIC ≤ 0.80 mg/mL). Bacillus megaterium, Legionella pneumophila, Listeria monocytogenes and Trichophyton spp. were the most sensitive species to both EOcom and EOtun. This study demonstrated the noteworthy antimicrobial activity of two commercial EOs and points out the remarkable efficiency of T. vulgaris EOtun on all tested bacterial and fungal species, certainly associated with its high content in carvacrol (85 %). These three oils could thus represent promising candidates for applications in water and food protections.