Synergistic antimicrobial activity of essential oils and oleoresins of cinnamon (Cinnamomum zeylanicum), clove bud (Syzygium aromaticum) and ginger (Zingiber officinale)

Abstract

The essential oils (EOs) and oleoresins (ORs) of Cinnamomum zeylanicum (cinnamon) and Syzygium aromaticum (clove bud), and Zingiber officinale (ginger) are highly important for therapeutical benefits. This study targeted on the evaluation of the antimicrobial activity of extracted EOs and ORs of three spices and their mixtures against five bacteria and two fungi compared to some commercial antimicrobial agents. The agar-disk diffusion assay and minimum inhibitory concentration (MIC) were done for evaluation of antimicrobial activity and the checkboard assay was done using fractional inhibition concentration to determine the synergism and efficacy of the essential oil and oleoresin combinations. The extracted EOs and ORs comprised a mixture of different chemical compounds and exhibited different in-vitro antimicrobial activity. The cinnamon bark oil exhibited the highest inhibition zones compared to other EOs, ORs and positive controls. The EOs and ORs of cinnamon and clove bud are highly effective against Aspergillus niger and Candida albicans as they exhibited significantly lower MIC values than antifungal agents. Nevertheless, MIC values of five kinds of bacteria implied no significant difference between cinnamon bark oil, clove bud oil and antibiotics. It was proven that EOs are more active in inhibiting microorganisms than ORs.