In vitro Synergistic Action of Honey and Essential Oils against Two Species of Aspergillus: A Preliminary Study

In order to evaluate the synergistic action of essential oils (EO) on the antifungal activity of honey, a comparative method of adding honey with and without EO to culture media was used. One variety of honey and five EO types were used to determine the minimum inhibitory concentration (MIC) against two clinical isolates of microfungi; namely Aspergillus niger and Aspergillus flavus. In a second step, lower concentrations of honey than the MIC were mixed with a set of sub-MIC of EO and then added to media to determine the minimum synergistic inhibitory concentration (MSIC). The MIC of honey without EO was 47% (v ⁄ v) against A. niger and 50% (v ⁄ v) against A. flavus. The MIC of EO varied strongly from one variety to another one with that of Eugenia caryophylata being the most effective against the tested Aspergillus species. When the EO was mixed with honey, a MIC drop was observed with each variety of EO. Isobolographic representation shows a synergistic action between honey and all EO types against the tested fungi. Further research studies are needed to elucidate and optimize the effective combination of these natural products in clinical practice.