In vitro evaluation of the antibacterial activities of the methanol, aqueous and n-hexane extracts of Ocimum lamiifolium from Ethiopia

Abstract

Ocimum lamiifolium (local name Dama Kesse, Amharic) is a medicinal plant in Ethiopia. Its leaves are squeezed and sniffed to treat coughs and colds. They are also used to treat eye infections and to stop nose bleedings. In the present study, leaves of O. lamiifolium were collected from their growing habitats. Dried leaf powders were extracted using methanol, distilled water and n-hexane. 25, 50, and 100 mg/ml doses of the extracts made in Tween 80 (2%) were screened for their antimicrobial activities against Staphylococcus aureus, Escherchia coli, Pseudomonas aeruginosa and Shigella boydii using disk diffusion assay. The inhibition zones due to the methanolic extract ranged from 0 (in S. aureus due to 25 mg/ml) to 12 mm (in E. coli due to 100 mg/ml). Inhibition zones due to the aqueous extract ranged from 8 mm in S. aureus and S. boydii to 12 mm in S. boydii at concentrations of 25 and 100 mg/ml, respectively. The n-hexane extract at 25 mg/ml resulted in inhibition zone that ranges from 7 mm (against S. aureus) to 11 mm (against E. coli) at 50 and 100 mg/ml doses. The minimum inhibitory concentration of S. boydii and E. coli was 10 mg/ml due to all the extracts. The minimum inhibitory concentrations on S. aureus were 10, 20 and 50 mg/ml due to the aqueous, n-hexane and methanolic extracts, respectively. P. aeruginosa was minimally inhibited at 10 mg/ml due to the methanol and aqueous extracts and 15 mg/ml due to the n-hexane extract. The methanol, aqueous, and n-hexane extracts of O. lamiifolium leaf extracts inhibited the test bacteria with significantly higher levels of inhibition zones than the negative control (T80). The positive controls (Tetracycline and Chloramphenicol) also showed significantly higher inhibition zones than the 100 mg/ml concentration of the extracts and T80 except that Chloramphenicol failed to inhibit S. aureus and P. aeruginosa. However, combination of Chloramphenicol with plant extracts raised their inhibition zones from zero to 23 and 25 mm in S. aureus and P. aeruginosa, respectively.