Abstract
Six essential oils (from oregano, thyme, clove, lavender, clary sage, and arborvitae) exhibited different antibacterial and antifungal properties. Antimicrobial activity was shown against pathogenic (Escherichia coli, Salmonella typhimurium, Yersinia enterocolitica, Staphylococcus aureus, Listeria monocytogenes, and Enterococcus faecalis) and environmental bacteria (Bacillus cereus, Arthrobacter protophormiae, Pseudomonas fragi) and fungi (Chaetomium globosum, Penicillium chrysogenum, Cladosporium cladosporoides, Alternaria alternata, and Aspergillus fumigatus). Oregano, thyme, clove and arborvitae showed very strong antibacterial activity against all tested strains at both full strength and reduced concentrations. These essential oils showed different fungistatic and fungicidal activities when tested by direct application and in the vapor phase. The genotoxic effects of these oils on HEL 12469 human embryo lung cells were evaluated using an alkaline comet assay for the first time, revealing that none of the oils induced significant DNA damage in vitro after 24 h. This study provides novel approaches for assessing the antimicrobial potential of essential oils in both direct contact and the vapor phase and also demonstrates the valuable properties of the phenol-free arborvitae oil. These results suggest that all the tested essential oils might be used as broad-spectrum anti-microbial agents for decontaminating an indoor environment.
Highlights
EOs from Origanum vulgare L., Thymus vulgaris L., Salvia sclarea L., and Lavandula angustifolia Mill. belonging to the Lamiaceae family have been used for their medicinal properties[1] for centuries; they possess antibacterial, antifungal[2,3,4,5], antioxidant, anti-inflammatory[6, 7] and analgesic properties[7]
Origanum vulgare (OR) and Thymus vulgaris (TY) EOs were extremely effective on all tested bacteria, with inhibition zones ranging from 26–54 mm
Eugenia caryophyllata and Thuja plicata EOs exhibited a lower degree of bacterial growth inhibition than OR and TY, while the greatest inhibition observed was caused by a phenol-free EO (AR) against Yersinia enterocolitica (p < 0.01)
Summary
EOs from Origanum vulgare L., Thymus vulgaris L., Salvia sclarea L., and Lavandula angustifolia Mill. belonging to the Lamiaceae family have been used for their medicinal properties[1] for centuries; they possess antibacterial, antifungal[2,3,4,5], antioxidant, anti-inflammatory[6, 7] and analgesic properties[7]. The vapor phase seems especially effective against fungi, and a number of studies have shown that EOs are more effective antifungals in the vapor state than in the liquid[20,21,22]. One possible explanation for this behavior is that the lipophilic molecules responsible for at least part of the activity might associate in the aqueous phase to form micelles, thereby suppressing their attachment to the organism, whereas the vapor phase allows free attachment[22]. In this situation, the observed antimicrobial activity arising from the volatilized components would result from a combination of the direct exposure www.nature.com/scientificreports/. The ability of some EOs to prevent the formation of Listeria monocytogenes[15] and Salmonella enterica[26] biofilm on stainless steel surfaces has previously been demonstrated
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