Antimicrobial resistance has become a serious threat to human health nowadays. This research aimed to explore the potential of plants to be used as antimicrobial agents against pathogenic bacteria. Three different extracts of Azadirachta indica (Neem) leaves (methanolic, ethanolic, and aqueous) were tested against 5 Gram-positive and 4 Gram-negative bacteria. For Gram-positive bacteria, ethanolic extract showed the best antimicrobial potential. Bacillus cereus was found more sensitive to ethanolic extract at 500 mg/ml conc. with a 21.1 mm zone of inhibition. For methanolic extract, at 500 mg/ml conc. Bacillus cereus and Methicillin-resistant Staphylococcus aureus were found more sensitive with 15.4 mm and 15.1 mm ZOI, respectively. Streptococcus pneumoniae was resistant to methanolic Neem extract. Three Gram negative bacteria: Klebsiella pneumoniae, Escherichia coli, and Salmonella typhimurium were resistant to all Neem leaves extracts. The best antimicrobial results of ethanolic and methanolic extracts against Pseudomonas aeruginosa were at 200 mg/ml conc. of each extract with 18.3 and 21.2 mm ZOI, respectively. Negative results were found for aqueous extract with all tested pathogenic bacteria. HPLC analysis of Neem leaves extracts depicted that benzoic acid was detected in ethanolic extract, while ferulic acid and 4-hydroxy benzoic acid were found in all three Neem leaf extracts. This study confirmed the antibacterial activity of Neem leaves against these bacterial strains and the possibility of employing this knowledge in new antibacterial drug development.
