HPLC Profiling of Phenolic Compounds and Flavonoids and Comparative In Vitro Antibacterial Activity of Vachellia karroo Leaf Extract from Northeastern Libya

Abstract

Vachellia karroo is a medicinal plant traditionally used in Africa, but its antibacterial potential and phytochemical constituents in northeastern Libya remain insufficiently investigated. The study aimed to evaluate the antibacterial activity of an 80% ethanolic leaf extract of V. karroo, compare its effects with conventional antibiotics, and characterize its phenolic and flavonoid constituents using high-performance liquid chromatography (HPLC). Leaves collected from Shahat, northeastern Libya, were extracted using a cooled maceration method. Antibacterial activity against Gram-positive and Gram-negative bacterial strains, including reference strains and clinical isolates, was assessed using agar well diffusion and minimum inhibitory concentration (MIC) assay. We compared the extract with amoxicillin-clavulanate, cephalexin, imipenem, and vancomycin. HPLC identified eight phenolic compounds and seven flavonoids. Catechol (13.32 µg/ml) and syringic acid (11.45 µg/ml) were the predominant phenolics, while naringin (15.45 µg/ml) and rutin (8.60 µg/ml) were the major flavonoids. The extract showed variable antibacterial activity, with the largest inhibition zone against Staphylococcus aureus (23 ± 3.0 mm), followed by clinical Pseudomonas aeruginosa (20 ± 7.0 mm) and Escherichia fergusonii (18 ± 6.0 mm). The smallest zone was observed against Acinetobacter baumannii (13 ± 2.0 mm). Activity exceeded that of selected antibiotics against certain isolates. The results report that the extract demonstrated variable in vitro antibacterial activity and diverse phytochemical constituents, warranting further investigation to identify active compounds and clarify its antibacterial potential.