The inhibitory effect of various essential oils on the in vitro growth of four bacterial species of skin flora

        Essential oils have been used for centuries by populations around the world for medicinal, cosmetic, and spiritual purposes. Although the antimicrobial activities of a number of essential oils have been studied extensively with respect to gastrointestinal pathogens, few scientific reports are available on the dermatologic application of essential oils other than tea tree oil. This study examined the efficacy of 12 essential oils in inhibiting the in vitro growth of four species of bacterial skin flora using the disk diffusion method. The following essential oils were tested for their antibacterial properties: bergamot, Virginia cedarwood, cinnamon bark, eucalyptus, garlic, laurel leaf, lavender, oregano, petitgrain, rose geranium, tea tree, and turmeric. We selected Staphylococcus aureus, S epidermidis, Propionibacterium acnes, and Pseudomonas aeruginosa for the study because of their association with many primary skin infections. Four standard of care antibiotics were included as positive controls. Zones of bacterial growth inhibition were measured after 24 to 48 hours of incubation at 37°C. Subsequently, five of the essential oils were solubilized in a minimum amount of methanol and diluted to various concentrations with nutrient broth for the determination of the minimum inhibitory concentrations (MIC). All experiments were performed in triplicate. The results showed that all 12 essential oils, at various concentrations, inhibited the growth of at least two different species of bacterial skin flora. Moreover, some essential oils were significantly more inhibitory than the standard of care antibiotics. The five most potent essential oils, in order of decreasing diameter of growth inhibition across species, were oregano (80 mm), garlic (70 mm), cinnamon bark (36 mm), laurel leaf (33 mm), and lavender population (28 mm). In addition, there was also a marked variation in bacterial susceptibility to essential oils, with P acnes being the most susceptible, followed by P aeruginosa, S aureus, and S epidermidis. These results suggest that essential oils could serve as potential therapeutic agents for the treatment and prevention of various dermatologic conditions with an underlying infectious etiology, including acne vulgaris, impetigo, folliculitis, furunculosis, hydradenitis suppurativa, secondarily infected pseudofolliculitis barbae, and burn wound infections.
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