ANTIBACTERIAL ACTIVITY OF PLANT-EXTRACTS - A COMPARISON OF AGAR DILUTION AND MICROTITRE BROTH DILUTION METHODS

Two plants commonly used by herbal practitioners in Kenya, Azadirachta indica A. Juss. (Meliaceae) and Ximenia americana var caffra (Sond.) Engl. (Olacaceae) were compared by agar dilution method and microtitre broth dilution method for determining the minimum inhibitory concentr ation (MIC) against 15 strains of Staphylococcus aureus and a referenc e strain of Pseudomonas aeruginosa. The MIC50 (mg/ml) obtained for A. indica against S. aureus ranged from 0.62 - 10 in agar dilution and 0. 31 - 1.25 in microtitre dilution method. P. aeruginosa reference strai n values were 5 and 1.25 in agar and broth dilution, respectively. X. americana var caffra had values of 2.5 in all strains of S. aureus and 10 for P. aeruginosa in agar dilution. It seems that for MIC determin ation of plant extracts, the microtitre broth dilution method is super ior to agar dilution method.