Inhibitory effects of cinnamon oil, acetic acid, and lactic acid on Escherichia coli ATCC 23631

Abstract

In this study, the antimicrobial activities of cassia oil (Cinnamomum cassia), acetic acid, and lactic acid, alone or in combination, against Escherichia coli ATCC 23631 were evaluated by the agar disk diffusion, broth dilution, and UV absorption determination methods. In the agar disk diffusion assays using the antibiotics ampicillin and nalidixic acid as the positive control, all three agents tested exhibited an effective inhibition against E. coli with inhibition zones ranging from 3.00 to 15.33 mm, compared to those of ampicillin and nalidixic acid ranging from 0.00 to 12.00 mm. In the broth dilution assays, the MBC (Minimum bactericidal concentration) values of cassia oil and organic acid were determined from 300 to 5.000 ppm in which cassia oil giving the best result. In both assays, acetic acid and lactic acid showed similar antimicrobial activities, which are lower than those of cassia oil or their combinations. The assays also suggested that the combinations of cassia oil and lactic acid showed a higher synergic effect than those of cassia oil and acetic acid. Although the antimicrobial activities of the combinations of cassia oil with the organic acids were not higher than using the pure oil, the use of these combinations would reduce the essential oil amount needed to inhibit E. coli.