Synergistic benefit of eugenia caryophyllata L. and cinnamomum zeylanicum blume essential oils against oral pathogenic bacteria

Abstract

Eugenia caryophyllata L. and Cinnamomum zeylanicum Blume essential oils offer great potential against the pathogens of oral cavity. Both of these essential oils have recently being used as antibiotics and antiviral agents. This study investigates the synergistic effect of E. caryophyllata and C. zeylanicum oils against known resistant bacteria in oral infection namely Enterococcus faecalis, Aggregatibacter actinomycetemcomitans, Streptococcus mutan and Streptococcus salivarius. The combination effect E. caryophyllata and C. zeylanicum were evaluated using checkerboard assays. Amoxicillin at concentration 0.1 mg/mL was used as positive control while each bacteria suspension (105 CFU/mL) was used as negative control. The minimum inhibitory concentration (MIC) and fractional inhibitory concentration index (FIC) were calculated to characterised interaction between the combinations. Both E. caryophyllata and C. zeylanicum oils possess antimicrobial activity against all 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. The synergistic antibacterial effect was significant toward E. faecalis, A. actinomycetemcomitans and S. mutans with FIC index is 0.5 and below. Partial synergy was produced in S.salivarus. The acceptable range for synergistic effect is between 0.16 mg/mL and 0.31 mg/mL. Above from 0.63 mg/mL are considered as additive and antagonistic effect. The combinations of these essential oils gave a stronger antibacterial activity and directly can replace the common use of antibiotics like Amoxicillin. This finding suggests a potential therapeutic benefit using the combination of E. caryophyllata and C. zeylanicum oils in the future management of oral infection.