The Effect of Cinnamon Essential Oil on Lactobacillus species
Authors: Adams Victoria R. , Johnson Amanda K. , Santos Fernanda B.O. , Santos Anael A. 
Published: June 2021

Antimicrobial properties of cinnamon essential oil solutions (EO) have been identified against pathogenic bacteria, but its effects on commensal microorganisms have not yet been described. In previous studies in our laboratory, cinnamon EO was tested against Salmonella Typhimurium and Escherichia coli utilizing the disc diffusion method. Zones of inhibition were measured, and cinnamon EO at 2 and 4% displayed great effectiveness against these microorganisms. Both microorganisms are Gram negative rods and have the capability to cause disease. Thus, the main objective of this study is to evaluate the effect of cinnamon EO on the commensal Gram positive microorganisms Lactobacillus acidophilus and Lactobacillus rhamnosus.

The Lactobacillus acidophilus (ATCC® 4356™) and Lactobacillus rhamnosus (ATCC® 7469™) inoculums were prepared by growing the bacteria in MRS (De Man, Rogosa and Sharpe) broth for 24h under microaerophilic conditions (5% CO2) at 37°C, yielding 6.9 ×108 CFU/ml. One hundred microliters of starting bacterial culture was spread onto MRS agar plates and dried for 15 minutes. Treatments were formed by creating cinnamon EO solutions of 0, 0.5, 1, 2 and 4% using 70% ethyl alcohol as the diluent. Each EO was vortexed and filtered using a 0.2 microliter sterile syringe filter. Twenty microliters of each EO were pipetted into a sterile paper disc and left to dry for 1h. Five paper discs of each treatment containing the EO were placed on standardized locations on each inoculated plate in duplicate. Additionally, three manufactured standard antibiotic paper discs of 5 mcg ciprofloxacin, 10mcg ampicillin, and 10mcg streptomycin were placed on separate plates in duplicate as controls. The zone of inhibition created by each EO or antibiotic was measured using a calibrated digital caliper. All data were analyzed using GLM procedure for ANOVA and Person correlation analysis.

The antimicrobial property of the EO observed as the zone of inhibition increased as the concentration of the EO increased for Lactobacillus acidophilus (r=0.86, p<0.0001). EO at 4% showed the greatest antimicrobial effect against Lactobacillus acidophilus compared to 2.0, 1.0, and 0.5% (2.59, 2.11, 0.0 and 0.0mm, respectively; p<0.0001). Lactobacillus rhamnosus showed resistance to EO at all concentrations studied with no zones of inhibition observed. All antibiotics had some effect against Lactobacillus rhamnosus, where ampicillin had the greatest effect compared to ciprofloxacin and streptomycin (6.62, 6.27, and 2.33mm, respectively; p<0.0001). Ampicillin had the greatest effect against Lactobacillus acidophilus compared to streptomycin (9.72 vs. 2.8mm, respectively; p<0.0001). However, L. acidophilus was shown to be resistant to ciprofloxacin with no zone of inhibition formed.

In conclusion, Lactobacillus species were generally resistant to cinnamon EO. These Lactobacillus species are commonly used as probiotics and are often adversely affected by antibiotic intake. Using cinnamon essential oil as an antibiotic alternative has shown to be a promising option with limited detrimental effects against the commensal bacteria. Further evaluation of the effects of cinnamon EO on commensal bacteria is needed to further determine the benefits of utilizing a natural alternative.

This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.