Azadirachta Indica (neem) Leaf: Chemical Composition and Antibacterial Activity As Determined by Different Polarity Solvents

The aim of this study was to investigate the antibacterial activity of Azadirachta indica leaf extracts against Staphylococcus aureus, Escherichia coli, Streptococcus pneumonia and Proteus mirabilis. This was performed using the disc diffusion method and the microdilution method (MIC). Solvents of variable polarity were used to extract the components of A. indica. The highest yield of extraction was obtained from methanol (3.30%), followed by ethanol (3.00%), ethyl acetate (1.50%) and hexane (0.90%). In general, A. indica leaf extracts exhibited broad spectrum antibacterial activity. The extracts of A. indica were shown to inhibit all tested strains in a dose dependent manner and the maximum activity was reported for the methanol extract followed by ethanol, ethyl acetate and hexane extracts. The most effective extract was methanolic leaf extract against P. mirabilis (inhibition zone equal to 28 mm and MIC equal to 0.47 μg/mL). Hexane extract showed no antibacterial activity against all strains tested. The chemical composition of the most effective extract, methanolic extract, has been analyzed using Liquid Chromatography–Mass Spectrophotometer (LC-MS) and the most dominant components were quercetin (20.4%), linoleic acid (14.5%), β-sitosterol (13.5%), myristic acid (11.3%) and oleic acid (7.3%). In conclusion, the potent antibacterial activity of A. indica is due to the polar compounds. The best solvents to extract the active antibacterial ingredients are solvents with high polarity such as ethanol and methanol.