Antimicrobial Activities of Two Essential Oils, Myrrh and Camphor

Objective: To determine the antimicrobial activities of two essential oils, Myrrh and Camphor, in six Gram-negative bacteria using Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) assays.

Method: Overnight cultures of Gram-negative anaerobes [Porphyromonas gingivalis(Pg), Prevotella intermedia(Pi)  and  Fusobacterium nucleatum(Fn)]and Gram-negative aerobes [Pseudomonas aeruginosa(Pa), Escherichia coli(Ec) and Actinobacillus actinomycetemcomitans(Aa)]were standardized at Optical Density (OD) 0.11 at 600 nm. The tested Gram-negative anaerobes are responsible for the formation of halitosis in humans. A 1:1 serial dilutions was prepared for the test agents, Camphor (Now foods, Bloomingdale, IL) and Myrrh (Aura cacia, Norway, IA), up to 1:128 dilutions.  Diluted test solutions were dispensed (100 microliter/well) in triplicates in a 96-well plate.  The control was a growth media without test agents.  Equal amount of 100 microliters of the standardized microbes were added to the diluted test agents including the controls in the 96-well plate to make a total volume of 200 microliter/well.  The plates were then incubated overnight at 37^oC in a regular incubator and anaerobic incubator (Coy Laboratory, Michigan) for aerobes and anaerobes, respectively. The MIC was determined by checking turbidity. Thirty microliters of the mixture from the clear wells were then plated on Brain Heart Infusion agar plates for aerobes and BHI agar plates with Hemin, L-Cystein and Vitamin K1 for the anaerobes to determine the MBC.

Result: Both Myrrh and Camphor showed a definitive MIC and MBC against all three Gram-negative anaerobes tested; however, there were no antimicrobial effect against two of the three Gram-negative aerobes with an exception of Camphor which displayed bactericidal effect against E. coli.

	Pg	Pi	Fn	Pa	Ec	Aa
Myrrh MIC/MBC	1:256/1:2	1:64/1:2	1:16/1:2	-/-	-/-	-/-
Camphor MIC/MBC	1:32/1:32	1:16/1:16	1:16/1:16	-/-	1:8/1:8	-/-

Conclusion: Both Camphor and Myrrh are effective against tested Gram-negative anaerobes.