Antibacterial Effect of Ginger Oil against Enterococcus faecalis

Objective: The occurrence of Enterococcus faecalis in failed endodontic treatment has been widely documented. Its ability to resist the antibacterial effect of currently available root canal medicaments has directed the research towards alternative herbal medicine. This study aimed to investigate the effect of ginger (Zingiber officinale Roscoe) rhizome oil against cultured E. faecalis. Method: Pure ginger oil was extracted via steam distillation technique, prepared as eight 2-fold dilutions with final concentrations range 0.04-5mg/ml in dimethyl sulfoxide (DMSO) and used in the microdilution bacterial susceptibility tests. In the suspension test, the E. faecalis inoculated overnight in brain heart infusion (BHI) broth at 37⁰C and 5% CO₂ and then exposed to ginger oil for 24h. Whilst in the anti-biofilm test, E. faecalis biofilms were grown in a 96-wells plate for 3 days prior to addition of oil for 24h. The Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) were determined using absorbance reading at 596 nm wavelength (OD₅₉₅) and colony counting on nutrient agar plates respectively. Ampicillin was used as positive control for both tests. Results: In both tests, ginger oil showed dose-dependent antibacterial activity against E. faecalis comparable to ampicillin. Ginger oil effectively inhibited up to 76% of growth of E. faecalis cells in suspension form and 31% in biofilm form at 5.0mg/ml. However, the suspension test showed significantly better antibacterial activity compared to the anti-biofilm test [MIC 0.31mg/ml and 1.25 mg/ml respectively, P<0.05]. Conclusion: Ginger oil showed promising antibacterial effect against E. faecalis grown as suspension as well as biofilm. This finding could suggest a potential usage as an antibacterial agent in endodontic treatment.