Antibacterial effect of combination of cinnamon essential oil and thymol, carvacrol, eugenol, or geraniol

Bacterial resistance to classic antibiotics is an alarming rate to put this into control with the use of natural products of plant derivatives. The objective of this study was to determine the phytochemical of cinnamon essential oil (EO) and to evaluate its antibacterial activity alone and in combination with some main components of EOs such as thymol, carvacrol, eugenol, or geraniol against three bacterial strains (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa). The phytochemical analysis of cinnamon EO was evaluated using gas chromatography-flame ionization detector and gas chromatography-mass spectrometer analysis. The antibacterial activity of tested compounds was determined by agar disk diffusion and minimum inhibitory concentration (MIC) assays. The checkerboard method was used to quantify the efficacy of cinnamon EO in combination with those compounds. The results showed that the major compound in the cinnamon EO was trans-cinnamaldehyde (91.01%). Cinnamon oil was the highest antibacterial activity with MIC of 0.005, 0.005, and 0.02 mg/mL against E. coli, S. aureus, and P. aeruginosa, respectively. Synergistic activity was shown only against S. aureus by the combination of cinnamon EO and thymol. The additive effect was found against E. coli when cinnamon EO was combined with thymol or carvacrol, and against S. aureus when cinnamon EO was combined with carvacrol. However, the combination of EO and thymol or carvacrol showed an indifference action against P. aeruginosa. The combination of cinnamon EO with thymol or carvacrol can be used as an alternative therapeutic agent for medical application and as a natural preservative.