Antibacterial efficacy of the pigmented and de-pigmented leaf extracts of Alstonia boonei Wild

Abstract

This work was carried out to evaluate the antibacterial efficacy of pigmented and de-pigmented petroleum ether and methanolic extracts of Tridax procumbens (whole plant). Phytochemical screening of these extract 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. The in-vitro antibacterial assay of these extracts revealed that the de-pigmented methanol extract showed appreciable activity against all the test organisms at 100 mg/ml- a broad spectrum inhibitory effect that was quite similar to that produced by the standard drug, Tetracycline at 0.5 mg/ml against Gram positive Staphylococcus aureus and Bacillus subtilis and was slightly better against Gram negative Pseudomonas aeruginosa. The minimum inhibitory (MIC), minimum bactericidal (MBC) concentrations and MBC/MIC ratio of the active extract ranged between 12.5-100 mg/ml and 25-100 mg/ml and 1.00 and 2.00 respectively. Purification of the active extract by preparative thin layer chromatography gave rise to polar fractions that exhibited similar/slightly better inhibitory activities against the test organisms at 50 mg/ml than the crude de-pigmented methanolic extract at 100 mg/ml. MIC, MBC and MBC/MIC ratios of the active fractions ranged between 12.5-50 mg/ml and 25-50 mg/ml and 1.00 and 4.00 respectively. The above findings suggest that the de-pigmented methanol extract of A. booni might be a valuable source of antibacterial substance(s) for the treatment of diarrhea, typhoid fever, urinary and gastrointestinal infections.