ABSTRACT 

Indiscriminate use of antibiotics is very common in developing countries, it is a major cause for development of antimicrobial-resistance. Thus it has now become essential to look for newer antibiotics mostly plants. Azadirachta indica is an Indian tree well known for its several pharmacological activities, and has been used against a few diseases in traditional medicine. This study was undertaken to screen for the phytochemical constituents as well as to investigate the antibacterial potential of Azadirachta indica leaf extract on Pseudomonas aeruginosa, Salmonella typhi, Staphylococcus aureus and Escherichia coli. The leaves of Azadirachta indica were collected, dried and was extracted with methanol and water. The susceptibility of these organisms to the methanol and aqueous extracts of Azadirachta indica were evaluated using the agar well diffusion method at various dilutions of 200 mg/ml, 100 mg/ml and 50mg/ml. Cultures of the test organisms were grown on Mueller Hinton agar plates. The agar plates were then incubated at 37°C for 24hours after which the zones of inhibition were measured. The results of this study demonstrated that, for all test organisms screened, the highest concentration (200mg/ml) of the methanol showed maximum antimicrobial action with zones on inhibition in the range of 9.0mm to 14.0mm. The methanol extract of Azadirachta indica demonstrated significant inhibitory activity against S. aureus compared to the other test microorganisms with an MIC value of 12.5mg/ml. Evaluation of the phytochemicals was made using standard methods. The phytochemical screening indicated the presence of alkaloids, saponins, tannins, flavonoids and phenolic content in the leaves. This result indicates that these plant materials have potential medicinal uses and the methanolic and water extracts can protect against some common microorganisms and thus may be a prospective therapeutic agent to combat antibiotic resistant bacteria.