Antimicrobial effects of cinnamon essential oil and cinnamaldehyde combined with EDTA against canine otitis externa pathogens.

The antimicrobial activity of cinnamon essential oil and cinnamaldehyde against bacterial and fungal pathogens associated with canine otitis externa, as well as the effect of their combination with EDTA were investigated. Antimicrobial susceptibility testing was performed using the broth microdilution method while spot-plating technique was used to determine their bactericidal activity. Time-kill kinetics and checkerboard assays were performed to confirm the bactericidal activity and combination effects of the compounds. Cinnamon oil and cinnamaldehyde exhibited antimicrobial activity against Gram-positive and Gram-negative pathogens, as well as Malassezia pachydermatis. Synergistic interaction was shown when EDTA (672 μg ml-1 ) was combined with cinnamon oil (41 μg ml-1 ) and cinnamaldehyde (22 μg ml-1 ) against Pseudomonas aeruginosa. Cinnamaldehyde exhibited significantly stronger antimicrobial activity than cinnamon bark oil. Cinnamon essential oil and cinnamaldehyde, either used alone or in combination with EDTA, were effective against the causative micro-organisms of canine otitis externa. The data suggest that cinnamaldehyde could be a promising antimicrobial agent against canine otitis externa. This study shows that cinnamon essential oil and cinnamaldehyde, especially the latter, could be used in combination with EDTA as novel treatment for sensitive and resistant bacterial and fungal pathogens involved in canine otitis externa.