The in vitro antimicrobial evaluation of commercial essential oils and their combinations against acne

Abstract

The investigated essential oil combinations resulted in at least 50% of the combinations displaying noteworthy antimicrobial activity. Most of the synergistic interactions do not necessarily correspond to the recommended layman's aroma-therapeutic literature, which highlights a need for scientific validation of essential oil antimicrobial activity. No antagonism was observed.

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

“…The chemical composition of each oil has previously been analyzed, and the major compounds reported, as included in the Supporting Information. [32,49] Essential Oil Antimicrobial Activity Essential oil combinations are often used with the goal of creating a synergistic effect. This goal, although desired, is not necessarily the outcome as shown in this and other studies.…”

“…This goal, although desired, is not necessarily the outcome as shown in this and other studies. [47][48][49][50][51][52][53] If one were to consider the aroma-therapeutic literature available to the layman, [22,23,31,33 -41] over 1500 combinations can be identified for skin conditions, and this study investigated only 247 of the possible combinations specifically focusing on pathogens associated with wounds. The MIC values for the investigated essential oils and combinations along with the ΣFIC values of the combinations were identified against the five reference strains associated with wound infections and is represented in Tables 1 and 2 ( Table 2 displays the combinations of essential oils with different chemotypes, species and plants parts).…”

“…The essential oil of Cinnamomum zeylanicum in this study was found to have stronger antimicrobial activity than that observed from C. zeylanicum by Orchard et al [32] for S. aureus, MRSA (ATCC 43300), MRSA (ATCC 33592-gentamycin resistant) and P. aeruginosa (MIC 0.13 -0.75 mg/ml compared to 1.00 mg/ml reported previously). The activity is attributed to the higher content of eugenol, [49] which was identified by Orchard et al [32] as being one of the primary essential oil compounds responsible for the antimicrobial activity. Cinnamomum zeylanicum inhib-ited E. coli with a noteworthy MIC value of 1.00 mg/ml in this study and this has been previously reported.…”

“…It is well-known that when oils are mixed in different ratios, a varied interaction may occur depending on the concentration of two components. [47][48][49]53] Synergistic combinations were evaluated at different ratios and plotted on isobolograms to demonstrate optimization of the most synergistic interactions, as demonstrated in Figure 1. Furthermore, from the varied ratio study, it can be deduced which concentration/s is/are the more favorable for a synergistic interaction to occur.…”

“…Unlike the Geranium species that predominantly differ quantitatively in composition of similar major compounds, the different chamomile plants differ qualitatively in chemistry which clearly impacts on the recorded antimicrobial activity. [32,48,49] The different oils thus may not yield the same biological results when used alone and in combination.…”