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

Antimicrobial properties of cinnamon essential oil have been identified against foodborne bacteria, but its effectiveness has not yet been fully determined. In a previous study, cinnamon essential oil at concentrations of 2% and 4% showed to be effective against Salmonella enterica serovar Typhimurium. However, its effect on a commensal, opportunistic and specialized pathogen like E. coli has not been completely described. Thus, the main objective of this study is to evaluate the effectiveness of cinnamon essential oil on Escherichia coli.

The Escherichia coli (ATCC 25404™) inoculum was prepared by growing the bacteria in Luria‐Bertani (LB) broth for 24 hours at 37°C, yielding 8.7×109 CFU/ml. One hundred microliters of the starting bacterial culture were spread onto LB agar plates and left to dry for 15 minutes. Treatments were formed by creating cinnamon essential oil solutions (EO) 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 was pipetted into a sterile paper disc (weight ranged of 0.0086–0.0090g) and left to dry for one hour. Five paper discs of each treatment containing the EO were placed on standardized locations on each inoculated plate in duplicate. The plates were then incubated at 37°C for 24 hours. Additionally, three manufactured standard antibiotic paper discs of 5 mcg ciprofloxacin, 10mcg ampicillin, and 10mcg streptomycin were placed on separate plates in duplicate as positive controls. The zone of inhibition created by each EO or antibiotic was measured using a calibrated digital caliper. All data were analyzed using the general linear model procedure for analysis of variance (ANOVA) and Pearson correlation analysis.

The antimicrobial property of the EO observed as the zone of inhibition increased as the concentration of the EO increased (r= 0.922, p<0.0001). EO at 4% showed the greatest antimicrobial effect against Escherichia coli compared to 2, 1, and 0.5% (6.7, 5.0, 0.88 and 0.0mm, respectively; p<0.0001). There was no significant difference (p>0.05) between the zone of inhibition of 0% and 0.5% EO. However, 2% EO showed increasing effectiveness against Escherichia coli with a zone of inhibition of 5.1mm (p<0.0001). The 2% EO concentration showed a greater zone of inhibition against E. coli than the ampicillin treatment (5.1 vs. 2.3mm, p<0.0001). All antibiotics had some effect against E. coli, and ciprofloxacin had the greatest effect; its effect was even greater than the 4% EO (7.6 vs. 6.7mm, p<0.0001). The 4% EO was not as effective as ciprofloxacin, but it was more effective than both streptomycin and ampicillin (6.7 vs. 6.1 and 2.3mm, respectively; p<0.0001).

In conclusion, cinnamon EO showed increasing antimicrobial properties against Escherichia coli as the concentration of oil increased. It proved to be more effective than two of the antibiotic controls at 4% concentration. Further evaluation of the effects of cinnamon EO is needed to determine the extent of its effectiveness against additional commensal and pathogenic organisms.

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