Antimicrobial Activity of Neem (Azadirachta indica) Bark Extract Against Clinical Bacterial Isolates in Delta State

The increasing prevalence of antibiotic-resistant bacterial pathogens has generated renewed scientific interest in plant-derived antimicrobial agents, and Azadirachta indica remains one of the most extensively used medicinal plants in southern Nigeria. This study investigates the antimicrobial activity of neem bark extracts against selected clinical bacterial isolates obtained from patients at the Delta State University Teaching Hospital in Oghara. Bark samples of Azadirachta indica were collected, air-dried, and extracted using ethanol, methanol, and aqueous solvents. Phytochemical screening was performed to identify bioactive constituents. Antimicrobial testing against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Streptococcus pyogenes was conducted using the agar well diffusion method. Minimum inhibitory concentrations (MIC) were determined by broth microdilution. Phytochemical analysis revealed the presence of alkaloids, tannins, saponins, flavonoids, and terpenoids in all extracts. The ethanolic extract demonstrated the broadest spectrum of activity, producing zones of inhibition ranging from 14 to 22 millimetres across the tested organisms. Staphylococcus aureus was the most susceptible organism with an MIC of 6.25 milligrams per millilitre for the ethanolic extract. Pseudomonas aeruginosa showed the highest resistance across all extracts. Comparative analysis with gentamicin and ampicillin reference antibiotics showed that neem extracts, while less potent, exhibited activity against two ampicillin-resistant Staphylococcus aureus isolates. These findings support further pharmacological investigation of neem bark as a source of novel antimicrobial compounds. Keywords: Azadirachta indica, antimicrobial activity, clinical isolates, MIC, Delta State.