Antimicrobial activity of propolis and essential oils and synergism between these natural products

Abstract

In the present study, Apis mellifera propolis and essential oils (EOs) obtained from aromatic plants were evaluated as alternative antimicrobials. We aimed to establish the antimicrobial activity of ethanolic extracts of propolis (EEP) from Apis mellifera and of EOs from Caryophyllus aromaticus, Zingiber officinale, Cinnamomum zeylanicum and Mentha piperita against 32 Staphylococcus aureus and Escherichia coli strains from human clinical specimens. The antimicrobials were diluted in agar and the minimal inhibitory concentrations (MIC) were found whereas MIC90% values were calculated. Time-kill curve assays using mixtures containing one quarter of MIC90% for EEP with all EOs as well cinnamon EO were performed. The cinnamon EO was found to be the most efficient, with MIC90% values of 1.22 and 0.96 mg x mL-1 respectively against S. aureus and E. coli, whereas MIC90% of EEP were 1.86 and 20.12 mg x mL-1 respectively against S. aureus and E. coli. The combinations of EEP with ginger and mint EOs, and cinnamon with ginger and clove EOs, showed synergistic effects. Consequently, further studies are necessary to confirm these activities in vivo and to evaluate the phytochemical characteristics of natural products.