Antimicrobial Activity of Isolated Compounds from Zanthoxylum gilletii Stem Bark Extract

Abstract

Background: Zanthoxylum gilletii, an important African medicinal plant, is widely used in traditional medicine for treating various ailments due to its rich phytochemical composition. However, despite its extensive ethnomedicinal applications, the specific bioactive compounds responsible for its antimicrobial properties remain insufficiently characterized. Aims: The study aims to isolate and characterize bioactive compounds from Zanthoxylum gilletii stem bark and evaluate their antimicrobial activity against selected bacterial and fungal pathogens. Methodology: Zanthoxylum gilletii stem bark was collected from Mabira Forest Reserve (0°23′54″N 33°0′59″E), Buikwe District, Uganda on 17th June 2022. The experiments were performed at the Department of Chemistry, Kyambogo University, between June 2022 and July 2023. Stem barks were shade dried, powdered, and extracted using Maceration technique with a mixture of methanol and dichloromethane (ratio 1:1) solvent. The extract was subjected to open column chromatography and identified using NMR spectroscopy and compared with literature information. Antimicrobial activity of crude extract and also the isolated compounds were assessed via disk diffusion against five bacterial and two fungal strains. Results: In this study, four known compounds: lupeol (1), stigmasterol (2), α-amyrin cinnamate (3) and α-amyrin acetate (4) were isolated from stem bark extracts of Zanthoxylum gilletii. This is the first-time compound 4 is reported in Zanthoxylum genus. The compounds had antimicrobial activities against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacter cloacae, Candida albicans and Aspergillus fumigatus. The extract and the compounds displayed inhibition against the microorganisms with diameters measuring 3.0±0.0 mm to 19.0±0.0 mm. The minimal inhibitory concentrations (MICs and MFCs) for active strains ranged from 6.25 to 150 mg/mL. Conclusion: The observed activities support the traditional use of this plant in treating various ailments by Ugandan communities.