Antimicrobial Potential of Two Essential Oils on Oral Bacteria

Objective: To determine antimicrobial potential of two essential oils, Eucalyptus and Sea Buckthorn, against three Gram-positive [Streptococcus mutans (Sm), Streptococcus sanguinis (Ss), Enterococcus faecali (Ef)] and three Gram-negative [Fusobacterium nucleatum (Fn), Actinobacillus actinomycetemcomitans (Aa), Escherichia coli (Ec)] bacteria using Minimum Inhibitory Concentration (MIC) & Minimum Bactericidal Concentration (MBC) assays.

Method: Overnight cultures of the six bacteria were standardized using a spectrophotometer at an optical density of 0.11 at 600 nm. The test agents Eucalyptus (Now foods, Bloomingdale, IL) and Sea Buckthorn (Balanceuticals Group, Chicago, IL) were serially diluted using microdilution method from 1:1 to 1:128.  The control was a nutrient broth without test solutions.  In a 96-well plate, 100 microliter per well of the diluted test solutions were plated in triplicates.  One hundred microliters of the organisms were added to the wells with test solutions including the controls.  The plates were incubated for 24 hours at 37^oC.  The MIC was determined after 24 hours of incubation by visual turbidity.  Thirty microliters from the clear wells were then plated on Brain Heart Infusion (BHI) agar plates for the aerobes and BHI plates with Hemin and Vit.  K₁ for the anaerobe (Fn) and were incubated for 24 hours to determine the MBC.

Result: Eucalyptus showed a definitive MIC/MBC on five test bacteria (Fn, 1:16/1:16 dil.; Ef, 1:2/1:2 dil.; Sm, 1:8/1:4 dil; Ss, 1:16/1:16 dil.; Ec, 1:8/1:4 dil.) except Aa, which showed no effect. Sea buckthorn displayed no antibacterial effect against the tested microorganisms.

Conclusion: Under conditions of the present study, Eucalyptus oil is effective against both Gram-positives and Gram-negatives of the tested microbes. Aa is highly resistant to both test solutions.  Sea Buckthorn oil did not exhibit any antimicrobial effect.