Antibacterial Effect of Cinnamon Oil Combined with Thyme or Clove Oil

Antibacterial effect of cinnamon oil combined with thyme or clove oil was studied in this paper. Agar dilution method was used to determine the minimum inhibitory concentrations (MICs) of the essential oils (EOs) of cinnamon, thyme, and clove oil against three Gram-positive bacteria (Bacillus subtilis, Bacillus cereus, and Staphylococcus aureus), and two Gram-negative bacteria (Escherichia coli and Salmonella typhimurium). The results showed that cinnamon was a promising antibacterial substance with MIC ranged from 0.1 to 0.4 μL mL⁻¹ for the five bacterial species. Agar dilution checkerboard method was used to test the combined antibacterial effect of cinnamon oil with thyme or clove oil. Combination of cinnamon and thyme oil showed an additive effect against all selected bacteria, and combination of cinnamon and clove oil displayed an additive effect against B. subtilis, B. cereus, S. aureus, and an indifferent effect against E. coli and S. typhimurium. Furthermore, gas chromatography-mass spectrometry (GC-MS) measurement was used to analyze the components of the EOs, and the main components of cinnamon, thyme, and clove were cinnamaldehyde, thymol, carvacrol and/p-cymene, and eugenol, respectively.