Assessment of Antibacterial Activity of Crude and Partially Purified Stem-Bark Extracts of Alstonia boonei Against Multidrug-Resistant Bacterial Pathogens

Abstract

Introduction: Medicinal plants remain important sources of bioactive compounds for antibacterial drug discovery. Although Alstonia boonei is widely used in traditional medicine, systematic data on the antibacterial activity of its stem bark fractions against clinically relevant multidrug-resistant (MDR) bacterial pathogens remain limited. This study therefore evaluated the antibacterial activity of crude and solvent-fractionated stem bark extracts of A. boonei against selected MDR bacterial strains. Methods: The stem bark was extracted using ethanolic maceration and subsequently fractionated through liquid–liquid partitioning to obtain n-hexane, ethyl acetate, and aqueous fractions. Antibacterial activity against Escherichia coli, Acinetobacter baumannii, Klebsiella pneumoniae, Klebsiella aerogenes, Pseudomonas aeruginosa, and Staphylococcus aureus was assessed using the agar well diffusion method. Zones of inhibition were measured and subjected to statistical analysis. Results: The crude extract exhibited moderate antibacterial activity against most tested organisms, with inhibition zones ranging from 12.33 ± 0.33 mm to 13.33 ± 0.89 mm. The highest activity was observed against P. aeruginosa and A. baumannii. Solvent fractionation enhanced antibacterial efficacy and revealed organism-specific activity patterns. The n-hexane fraction showed the strongest inhibition against S. aureus (16.67 ± 0.67 mm), K. aerogenes (15.66 ± 0.33 mm), and A. baumannii (14.67 ± 0.89 mm), while the ethyl acetate and aqueous fractions exhibited the highest activity against K. aerogenes (16.67 ± 0.67 mm) and P. aeruginosa (16.33 ± 0.33 mm), respectively. Conclusion: This study addresses an important knowledge gap by systematically evaluating the antibacterial activity of crude and polarity-based fractions of A. boonei stem bark against clinically relevant MDR bacterial pathogens. The findings demonstrate the influence of solvent polarity on antibacterial potency and support A. boonei as a promising source of lead compounds for future antibacterial drug development.

Keywords: Alstonia boonei, Phytochemicals, Fractionation, Bacteria, Antibiotic resistance, Ethnomedicine