Potential of cinnamon (Cinnamomum verum) oil to control Streptococcus iniae infection in tilapia (Oreochromis niloticus)

In this study, four essential oils-cinnamon oil, leech lime oil, lemongrass oil, and turmeric oil-were examined for their antimicrobial activities against Streptococcus iniae, a bacterium that is pathogenic in fish, in which it causes streptococcosis. Cinnamon oil was the most potent antimicrobial agent among these oils, with a minimal inhibitory concentration (MIC) of 40 mu g/ml. By using gas chromatography-mass spectrometry (GC-MS), it was found that the major components of cinnamon oil were cinnamaldehyde (90.24), limonene (2.42%), cinnamyl acetate (2.03%), linalool (1.16%), and alpha-terpineol (0.87%). Of these compounds, only cinnamaldehyde exhibited antimicrobial activity against S. iniae, with an MIC of 20 mu g/ml. In an in vivo trial, no mortality was apparent in fish fed on fish diets supplemented with 0.4% (w/w) of cinnamon oil and with 0.1% (w/w) of oxytetracycline 5 days prior to infection with S. iniae. These results indicate that cinnamon oil had a protective effect on experimental S. iniae infection in tilapia, and thus has the potential to replace the antibiotics used to control this disease.