Abstract
The present study was carried out to evaluate the antimicrobial activity of ethanolic extracts of Azadirachta indica and Psidium guajava against four clinically important bacteria namely Staphylococcus aureus, Salmonella typhi, E. coli and Pseudomonas aeruginosa. The antimicrobial activity of extracts was done with agar well diffusion assay in plates containing MHA media. A fresh bacterial culture of 100 mu l containing approximately 1 x 10(6) CFU/ml of test microorganism was inoculated onto media plates and spread homogeneously. Wells of 6 mm in diameter were punched off in MHA plates with pH 6.0, 7.5, and 9.0, filled with different quantities of extracts in various combinations, and incubated for 24 h at 35 degrees C and 37 degrees C. The antimicrobial activity of ethanolic extracts showed that all the combinations of extracts were effective against the test microorganisms. The pH 6.0 and temperature 35 degrees C with concentration of each extract at 25 mg/mu l was found to be the inhibitoriest against all the bacteria tested. The diameter of zones of inhibition at pH 6.0 exhibited by S. aureus were in the range of 17-30 mm, E. coli (18-26 mm) and S. typhi (9-12 mm) and the zone of inhibition for P. aeruginosa was observed between 19-23 mm. The antimicrobial activity of the ethanolic extract was reduced when the same combination of extract concentration was tested at 37 degrees C. The antimicrobial activities of both the extracts were severely affected negatively at pH 9.0. The results contained in this study indicate that these plant extracts have enormous antimicrobial potential, and may be exploited for the treatment of various infectious diseases.