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

ObjectiveThe study investigated the efficacy of commercial essential oil combinations against the two pathogens responsible for acne with the aim to identify synergy and favourable oils to possibly use in a blend. Materials and MethodsAntimicrobial activity was assessed using the minimum inhibitory concentration (MIC) assay against Staphylococcus epidermidis (ATCC 2223) and Propionibacterium acnes (ATCC 11827), and the fractional inhibitory concentration index (sigma FIC) was calculated. Combinations displaying synergistic interactions were further investigated at varied ratios and the results plotted on isobolograms. ResultsFrom the 408 combinations investigated, 167 combinations were identified as displaying noteworthy antimicrobial activity (MIC value 1.00 mg mL(-1)). Thirteen synergistic interactions were observed against S. epidermidis, and three synergistic combinations were observed against P. acnes. It was found that not one of the synergistic interactions identified were based on the combinations recommended in the layman's aroma-therapeutic literature. Synergy was evident rather from leads based on antimicrobial activity from previous studies, thus emphasizing the importance of scientific validation. Leptospermum scoparium J.R.Forst. and G.Forst (manuka) was the essential oil mostly involved in synergistic interactions (four) against S. epidermidis. Cananga odorata (Lam.) Hook.f. and Thomson (ylang ylang) essential oil was also frequently involved in synergy where synergistic interactions could be observed against both pathogens. The combination with the lowest MIC value against both acne pathogens was Vetiveria zizanioides Stapf (vetiver) with Cinnamomum verum J.Presl (cinnamon bark) (MIC values 0.19-0.25 mg mL(-1)). Pogostemon patchouli Benth. (patchouli), V. zizanioides, C. verum and Santalum spp. (sandalwood) could be identified as the oils that contributed the most noteworthy antimicrobial activity towards the combinations. The different chemotypes of the essential oils used in the combinations predominantly resulted in similar antimicrobial activity. ConclusionsThe 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. Resume Objectifl'etude a examine l'efficacite d'associations d'huiles essentielles commercialisees contre les deux pathogenes responsables de l'acne dans le but d'identifier des synergies et les huiles dont le melange pourrait etre benefique. Materiels et Methodesl'activite antimicrobienne a ete evaluee par un dosage de la concentration minimale inhibitrice (CMI) contre Staphylococcus epidermidis (ATCC2223) et Propionibacterium acnes (ATCC11827), et l'indice de concentration inhibitrice fractionnaire (sigma FIC) a ete calcule. Les associations montrant des interactions synergiques ont ete etudiees de maniere plus approfondie selon differents rapports et les resultats ont ete places sur des isobologrammes. Resultatssur les 408 associations etudiees, 167 ont ete identifiees comme montrant une activite antimicrobienne notable (CMI 1.00 mg mL(-1)). Treize interactions synergiques ont ete observees contre S. epidermidis et trois associations synergiques ont ete observees contre P. acnes. On a constate que l'une des interactions synergiques identifiees etait basee sur les associations recommandees dans la litterature aromatherapeutique grand public. La synergie etait evidente plutot a partir de pistes basees sur l'activite antimicrobienne mise en evidence dans des etudes anterieures, ce qui souligne ainsi l'importance de la validation scientifique. Leptospermum scoparium J.R.Forst. and G.Forst (manuka) etait la principale huile essentielle impliquee dans des interactions synergiques (quatre) contre S. epidermidis. L'huile essentielle de Cananga odorata (Lam.) Hook.f. and Thomson (ylang ylang) etait aussi souvent impliquee dans des synergies lorsque des interactions synergiques ont pu etre observees contre les deux pathogenes. Les associations ayant les valeurs de CMI les plus basses contre les deux pathogenes lies a l'acne etaient Vetiveria zizanioides Stapf (vetiver) et Cinnamomum verum J.Presl (ecorce de cannelle) (valeurs de CMI de 0.19 a 0.25 mg mL(-1)). Pogostemon patchouli Benth. (patchouli), V. zizanioides, C. verum et Santalum spp. (bois de santal) ont pu etre identifiees comme les huiles qui contribuaient de facon la plus notable a l'activite antimicrobienne dans les associations. Les differents chemotypes des huiles essentielles utilisees dans les associations ont principalement entraine une activite antimicrobienne similaire. Conclusionsles associations d'huiles essentielles etudiees ont mis en evidence une activite antimicrobienne notable pour au moins 50 % des associations. La plupart des interactions synergiques ne correspondent pas necessairement a la litterature aromatherapeutique grand public recommandee, ce qui met en evidence un besoin de validation scientifique de l'activite antimicrobienne des huiles essentielles. Aucun antagonisme n'a ete observe.