The Influence of Carrier Oils on the Antimicrobial Activity and Cytotoxicity of Essential Oils

Abstract

The topical use of essential oils requires dilution into a carrier oil; however, scientific evidence regarding the antimicrobial efficacy and cytotoxicity when a carrier oil is combined with an essential oil is lacking. This study sets out to determine the antimicrobial activity and cytotoxicity of 23 essential oils combined with six known carrier oils. Gas chromatography-mass spectrometry/flame ionization detector (GC-MS/FID) was used to characterize the methyl esters of the carrier oils. The antimicrobial activity of the carrier oils alone and in combination with the essential oils was investigated using the broth microdilution assay against 11 skin pathogens and the cytotoxicity was determined using the brine shrimp lethality assay. The interactive profiles of the combinations for both antimicrobial activity and the cytotoxicity were analysed and calculated using the fractional inhibitory concentration index (ΣFIC). The carrier oils demonstrated no antimicrobial antagonism when combined with the essential oils and the overall cytotoxicity of the majority of the combinations was decreased. The carrier oils that could be identified as enhancing the antimicrobial activity and decreasing the cytotoxicity were Aloe vera Mill. and Simmondsia chinensis C.K.Schneid (Jojoba oil), with an overall reduction in essential oil cytotoxicity of 87.5% at 24 hrs and 85% at 48 hrs by A. vera. Five of the essential oils (when diluted in A. vera and S. chinensis carrier oils) demonstrated enhanced antimicrobial activity against pathogens such as Brevibacterium epidermidis, B. linens, and P. aeruginosa with MIC values ranging from 0.09 to 0.50 mg/mL (and ΣFIC 0.14-0.39). The study could conclude that the carrier oils are complementary to essential oil formulations, mostly reducing cytotoxicity and in some cases enhancing the antimicrobial activity.

Wound Pathogens: Investigating Antimicrobial Activity of Commercial Essential Oil Combinations against Reference Strains

“…(avocado), which have been shown to enhance antimicrobial activity of essential oils while decreasing the toxicity. [80] Based on the results presented here, it could be determined that only a slight variation in antimicrobial activity exists between different chemotypes of essential oils, yet synergy was more common in the chemotype that displayed more notable antimicrobial activity, as was noted for R. damascena and V. zizanioides. Antimicrobial activity was also shown to vary according to different parts of a plant (as shown by the Cinnamomum spp.)…”

Potential use of essential oils in cosmetic and dermatological hair products: A review

“…The safest way for topically EO application is following the specific instructions based on scientific data and the suitable carrier for its dilution 70,72 . In addition to the use of isolated or associated with carrier substances, there are cosmetic formulations that promote specific benefits for both scalp and hair shaft.…”

Polymeric Carriers Designed for Encapsulation of Essential Oils with Biological Activity

“…The mechanism of the antimicrobial actions of EOs, which cause damage to the bacterial cell wall or cell membranes, inducing complete cell disorganization and disruption, is also mentioned. Moreover, it is also highlighted that the presence of peripheral cytoplasmic condensations [ 40 ], irreversible loss of viability [ 41 ], increase in cell membrane permeability [ 42 ], and partial solubilization of the cell membrane by fatty acids, leads to the release of membrane proteins and uncoupling of oxidative phosphorylation, or enzyme and nutrient uptake inhibition; thus, causing bacteriostasis [ 43 ].…”