Antibacterial Efficacy of The Pigmented And De-pigmented Leaf Extracts of Alstonia boonei De Wild

Abstract

Antibacterial efficacy of pigmented and de-pigmented petroleum ether and methanolic leaf extracts of Alstonia boonei was investigated. Phytochemical screening of these extracts using standard methods revealed that the pigmented and de-pigmented petroleum ether extract showed the strong presence of steroidal nucleus only, while the pigmented and de-pigmented methanol extracts revealed the presence of alkaloids, saponins, tannins, flavonoids, steroidal nucleus and cardiac glycosides with the de-pigmented extract showing a stronger presence of these constituents. The in-vitro antibacterial efficacy of these extracts revealed that the de- pigmented methanol extract showed appreciable activity against all the test organisms at 100mg/ml; a broad spectrum inhibitory effect that was quite similar to that produced by the standard drug, Erythromycin at 0.5mg/ml. The antibacterial efficacy of the active extract was only slightly enhanced at increased temperatures. The minimum inhibitory (MIC), minimum bactericidal (MBC) concentrations and MBC/MIC ratio of the active extract ranged between 6.25- 50mg/ml, 25-100mg/ml and 1.0-4.0 respectively. Fractionation of the active extract by vacuum liquid chromatography gave rise to fractions that exhibited less inhibitory activities against the test organisms at 20mg/ml than the crude de-pigmented methanolic extract at 100mg/ml. MIC, MBC and MBC/MIC ratios of the active fractions also ranged between 100-200mg/ml, 50- 200mg/ml and 1.0-2.0 respectively. The above findings suggest that the de-pigmented methanol extract of A. boonei might be a valuable source of antibacterial agents for the treatment of diarrhoea, typhoid fever, urinary and gastrointestinal infections.