Abstract
There is a huge concern in the medical field concerning the emergence of bacterial resistance to antibiotics. Essential oils are a source of antibacterial compounds that can overcome this problem. Ten essential oils that are commercially available were investigated in the present study: ajowan, basil, German chamomile, Chinese cinnamon, coriander, clove, lemongrass, Spanish lavender, oregano and palmarosa. Their direct, synergistic and indirect antibacterial activities were evaluated against different human pathogenic Gram-positive and Gram-negative strains. To evaluate their possible use in clinics, the cytotoxicity of these essential oils was also tested on keratinocyte and epithelial cell lines. Except for the Chinese cinnamon, coriander and lemongrass, all other essential oils presented no cytotoxicity at 32 and 16 μg/mL. The highest indirect antibacterial activities were observed with the palmarosa and Spanish lavender in association with penicillin V. These two associations presented a 64-fold decrease against a resistant strain of Staphylococcus aureus, however, at a cytotoxic concentration. It can also be highlighted that when tested at a non-cytotoxic concentration, the activity of oregano in association with penicillin V presented an eight-fold decrease. These results show the interest to use essential oils in combination with antibiotics to reduce their concentrations inside drugs.
Highlights
The bacterial resistance to antibiotics remains a huge threat to public health and is still associated with high mortality and morbidity [1]
A residual cell (RC) viability of 80%, after 72 h of culture, was considered as a minimum requirement to express the possible local tolerance, i.e., when essential oils are used in a topic or an oral way of administration for veterinary or human purposes
Used at a sub-minimum inhibitory concentration (MIC) concentration, the Spanish lavender and the palmarosa can be highlighted since they can restore the activity of the penicillin V against
Summary
The bacterial resistance to antibiotics remains a huge threat to public health and is still associated with high mortality and morbidity [1]. Despite the awareness of this global situation, the list of resistant pathogenic strains has continued to increase over the last twenty years, with a resistance extended to more than one family of antibiotics [5] To address this increase in bacterial resistance, it is necessary to have better management of the antibiotics consumption in both human and veterinary health, and to promote scientific research to find new molecules with antibacterial activity that can inhibit the bacterial resistance and/or work in synergy with antibiotics [6,7]. Lemongrass—Cymbopogon citratus (DC.) Staph., Spanish lavender—Lavandula stoechas L., oregano—Origanum compactum Benth., and palmarosa—Cymbopogon martinii var. motia (Roxb.) W.Watson
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