In vitro Antibacterial Activity and Antibiotic-Modulating Effects of a Methanol–Water Moringa oleifera Leaf Extract against Selected Bacterial Isolates from Libya

Abstract

Antimicrobial resistance has increased interest in plant-derived antimicrobial candidates. This laboratory-based in vitro study evaluated a methanol–water extract of locally collected Moringa oleifera leaves against selected isolates of Staphylococcus aureus, Staphylococcus epidermidis, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Antibacterial activity was assessed by agar well diffusion, while minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by broth dilution. Antibiotic susceptibility was evaluated by disk diffusion, and a modified disk-soaking procedure was used to screen for changes in antibiotic inhibition-zone diameters after exposure to the extract. The extract inhibited all tested isolates, with the largest inhibition zone against S. aureus (20.0 ± 1.2 mm) and the smallest against P. aeruginosa (12.0 ± 0.8 mm). Reported MIC/MBC values ranged from 10/20 mg/mL for S. aureus to 40/50 mg/mL for P. aeruginosa. The extract was associated with increased inhibition zones for selected antibiotic–isolate combinations, including amoxicillin–clavulanic acid against S. aureus and meropenem against P. aeruginosa. These findings provide laboratory evidence that locally cultivated M. oleifera leaves contain antibacterial activity and identify promising antibiotic–extract combinations for confirmation with standardized interaction assays, broader isolate collections, and subsequent translational studies.