Abstract:
Eucalyptus camaldulensis and E. tetragona are the species of genus Eucalyptus in Ethiopia known for medicinal values of its essential oils. The essential oil composition of these species may vary due to genetic difference. In this study, essential oil composition and antibacterial activities of the leaves of E. camaldulensis and E. tetragona leaf essential oils were analyzed. The oil was extracted by steam distillation by using Clevenger apparatus and their compositions were analyzed by using Gas Chromatography-Mass Spectroscopy. Antibacterial activities of the essential oils at different concentrations were assessed with doxycycline and Ethanol used as positive and negative control respectively. The results showed that the essential oils extracted from E. camaldulensis and E. tetragona contained 18 and 15 compounds, respectively. Chemical composition of essential oils E. camaldulensis contained oxygenated monoterpene, hydrocarbon monoterpene, oxygenated sesquiterpene, and hydrocarbon sesquiterpene of 64.33%, 25.28%, 0.34%, and 4.52% respectively and E. tetragona contained 94.16%, 3.99%, 1.36% 0.33% respectively. The extracted essential oils were evaluated for their antibacterial activities using disc diffusion method against two bacterial species (S. aureus and E. coli). E. tetragona extracts were shown to have higher antibacterial activities with maximum zone of inhibition of (17.66±0.58 mm) against S. aureus and minimum zone of inhibition (8.33±0.57mm)against E. coli than E. camaldulensis extract with the maximum zone of inhibition (15.67±0.57 mm) against S. aureus while minimum zone of inhibition (7.32±0.58 mm) against E. coli. The MIC of the extract determined using broth dilution test against both bacterial species and the MIC of E. tetragona were 0.32 and 0.625 mg/ml for S.aureus and E. coli respectively, whereas MIC of E. camaldulensis against S. aureus and E. coli were 1.25 and 2.5 mg/ml respectively. In conclusion both the species of Eucalyptus showed antibacterial activity and the oil extract of E. tetragona indicated more antibacterial activity than the oil extract of E. camaldulensis against the studied bacterial species.
