Neem Seed Methanolic Extract Scavenges Free Radicals and Demonstrate Bacterial Growth Inhibition Potential

This study aimed to assess the free radical scavenging activity antibacterial and bacterial growth inhibitory potential of the Azadirachta indica (neem) seed methanolic extract (NSME). NSME was subjected to phytochemical screening and the antioxidant activity was assayed by determining the 2-diphenyl-1-picrylhydrazil (DPPH) and hydroxyl radical scavenging activities (RSA) as well as total antioxidant capacity (TAC). Pseudomonas aeruginosa and Staphylococcus aureus were the target microbes with gentamicin (CN) and 5% DMSO as positive and negative controls, respectively. Phytochemical screening revealed that the extract contains alkaloids, anthraquinones, flavonoids, phenols, steroids, tannins and terpenoids. The flavonoids and phenolic content were 65.25 ± 3.189 mg QE/g and 442.333 ± 3.055 mg GAE/g respectively. NSME showed high RSA equivalent to 85.83% ± 0.16% DPPH RSA and 87.09% ± 0.380 hydroxyl RSA at 1000 μg/mL. The TAC of the extract (32.51 ± 1.39 mg/100 mg ascorbic acid) was significantly higher (p<0.05) than that of butylated hydroxytoluene (22.87 ± 0.69 mg/100 mg ascorbic acid). The extract showed preliminary inhibitory activity against P. aeruginosa with the greatest inhibition at 1000 mg/mL with no noticeable inhibitory activity against S. aureus. Molecular docking revealed the interactions of phytol to penicillin-binding protein 1A and quercetin to DNA gyrase subunit B which obeyed the druggability and pharmacokinetic results that support NSME as one of the promising indigenous medicinal plants with antioxidant and antimicrobial properties.