Abstract

Most agents used by humans in the treatment of diseases are of plant origin. Azadirachta indica(neem) is a tree which has been found to possess antibacterial, antifungal, anti-inflammatory, anti-tumour properties and is also used as a pesticide. In this work, antibacterial effect of methanolic and aqueous extracts of the stem bark of A. indica was determined using minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and Kill-time of extracts as indices. Clinical bacterial isolates such as Escherichia coli, Salmonella spp andStaphylococcus aureus were used as test organisms. For the aqueous extracts, a minimum concentration of 43.75 mg/ml was found to inhibit the growth of E. coli in nutrient broth. S. aureuswas inhibited by 87.50 mg/ml and Salmonella spp by 175 mg/ml. Salmonella spp and S. aureuswere killed by a minimum concentration of 175 mg/ml but at 1200 and 130 s respectively; while E. coli was killed at 87.50 mg/ml at 600 s. For methanolic extract, 43.75, 87.50 and 175 mg/ml concentrations inhibited the growth of E. coli, Salmonella spp and S. aureus respectively in nutrient broth. Both Salmonella spp and S. aureus were killed by 175 mg/ml at 600 and 60 s respectively in nutrient broth, while E. coli was killed by 250 mg/ml at 1200 s. A comparison of the effects of commonly used antibiotics and the extracts of A. indica at 1, 3 and 5 mg per disc on the bacterial isolates by disc diffusion method, showed that the extracts had similar effects on the bacteria as the fluoroquinolones. The crude extracts of A. indica were able to inhibit the growth of bacterial isolates in vitro, it therefore means that the plant has antibacterial properties. It is recommended that further work be done to identify the specific ingredient(s) responsible for the effect, purify it and standardize same as a drug against bacteria.