Evaluation of antimicrobial activity of a Sudanese herbal plant (<i>Piliostigma reticulatum</i>)

Abstract

Background: Piliostigma reticulatum is a plant that is found in a wide area of Sahelo-Sudanian region of Africa. It is widely used in Africa as a traditional medicine for the treatment of a wide range of diseases including epilepsy, anxiety, and agitation. The leaf extract was found to have antimicrobial activity. In Sudan (Nuba mountains in particular), it is widely used to dress new wounds and as well puerperal sepsis. Moreover it’s fruit is eaten and used to prepare juice. Reported studies concerning antimicrobial activity of the plant in Sudan could not be found. This study therefore aimed to evaluate the antimicrobial action of Ethanolic and Aqueous extract of leaves and barks of the plant.

Methods: Barks and leaves of P. reticulatum were obtained from North Kordofan State. They were then air dried in the shade and milled into powder using Mortar.
Methanolic and water extract of each part of the plant was prepared using a Soxhlet apparatus. The following concentrations of extracts of each part (bark and leaves) of the plant were prepared using Distilled water (50 mg/ml, 25 mg/ml, 12.5 mg/ml, 6.25 mg/ml, 3.125 mg/ml, and 1.56 mg/ml). Antimicrobial action of the different concentrations of the extracts of the two parts of the plant on selected bacterial and fungal species was performed using well diffusion technique. Antimicrobial susceptibility of the tested organisms to serial concentrations (40 μg, 20 μg, 10 μg, and 5 μg) of three antibacterial (Gentamicin, Ampicillin, and Tetracycline) and 2 antifungal (Nystatin and clotrimazole) was evaluated using well diffusion method.

Results: The methanolic extract of P. reticulatum leaves showed high antibacterial activity against Bacillus subtilis (inhibition zone 22 mm), S. aureus (25 mm), P.
aeruginosa (23 mm), and E.coli (20 mm). The extract also showed antifungal activity against A. niger (23 mm) and C. albicans (23 mm). The aqueous extract revealed low activity against P. aeruginosa (10 mm) and no action on the rest of the microorganisms.

Conclusion: In this study, the methanolic extract of the leaves inhibited the growth of all the tested bacteria and fungi but with varied activity (inhibition zones between 8 mm and 20 mm). The highest activity was against B. subtilis (inhibition zone 20 mm), followed by A. niger and C. albicans (19 mm each), then P. aeruginosa (18 mm). Methanolic extract of the leaves revealed moderate activity against E. coli (13 mm) and low activity against S. aureus (8 mm).