This investigation was aimed at determining the antibacterial activity of extracts of stem bark of Azadirachta indica A. Juss on some clinical isolates. Results of preliminary analysis showed that the stem bark of A. indica possesses alkaloids, flavonoids, tannins, cardiac glycosides, phlobotannins and phenols. The ethanol extract produced higher antibacterial activity against all test microorganisms compare to the acetone extract, the highest Proteus vulgaris (15 mm) with ethanol extract at 500 mg/ml, and Staphylococcus aureus (13.5 mm) with acetone extract at 500 mg/ml respectively. Both the extracts produced definite strong antibacterial activity against test organisms at 50 to 1000 mg/ml concentration. Statistical analysis (t cal.-0.42) revealed that there was no significant difference among the antibacterial activities of ethanol and acetone extracts of A. indica against the test organisms. At pH value 2.0, the antibacterial activity of ethanol extract at 500 mg/ml was increased significantly against P. mirabilis (diameter of zone 20.0 mm) compared to the untreated one at pH 4.2 (diameter of zone 9.0 mm). In the case of S. aureus at pH 8.0 there was an increase in antibacterial activity of the ethanol extract (diameter of zone 29.0 mm) when compared to untreated extract at pH 4.2 (diameter of zone 14.0 mm). The minimum inhibitory concentration (MIC) values for acetone extract ranged from 100 to 500 mg/ml for the test organisms, and for ethanol extract the value was 200 mg/ml for all the test organisms. In case of test organisms, the minimum bactericidal concentration (MBC) value was 500 mg/ml for both extracts. So, the use of A. indica for treatment of urinary tract infection may be justified.
Key words: Phytochemicals, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), Azadirachta indica, Proteus mirabilis.