Interaction of combined essential oils from syzygium aromaticum and cinnamomum verum on oral pathogenic bacteria

Abstract

Syzygium aromaticum (S. aromaticum) and Cinnamomum verum (C. verum) essential oils offer great potential against the pathogens of the oral cavity. Chemical constituents for both essential oils have been reported to have antibacterial agent. This study investigates the interaction effect of S. aromaticum and C. verum oils against known resistant bacteria in oral infection of Enterococcus faecalis, Aggregatibacter actinomycetemcomitans, Streptococcus mutan and Streptococcus salivarius. The analysis of oils was done using GC and GC-MS methods to quantify the chemical constituents. Most of the constituents found in S. aromaticum and C.verum oils contained terpenes and oxygenated compounds which contributed to antibacterial activity. The combination effects of S. aromaticum and C. verum were evaluated using checkerboard assays. Amoxicillin at concentration of 0.1mg/mL was used as positive control while each bacteria suspension of 105 CFU/ml was used as negative control. The minimum inhibitory concentration (MIC) and fractional inhibitory concentration index (FIC) were calculated to characterize the interaction between the oil combinations. Both S. aromaticum and C. verum oils possess antimicrobial activity against the four bacteria when used on its own or in combination. In combination, the MIC values were reduced for all bacteria compared when in single form. Both of these essential oils have maximum antibacterial potential at combination ratio of 1:1. At other ratio 9:1, 3:7 and 6:4 the combinations showed poor antibacterial activity against the four selected bacteria. The combinations of these essential oils within the acceptable range for synergistic of 0.02 to 0.31 mg/mL with the FIC value =0.5 have shown good antibacterial activity and directly can substitute the common use antibiotics like Amoxicillin. This finding suggests a potential therapeutic benefit using the combination of S. aromaticum and C. verum oils to overcome oral infection in future.