Antibacterial Evaluation of Some Plant Extracts Against Some Human Pathogenic Bacteria

The aqueous, different solvent extracts and isolated constituents of eight higher medicinal plants viz., Argemone mexicana, Caesalpinia coriaria, Decalepis hamiltonii, Euphorbia tirucalli, Leucas aspera, Phyllanthus amarus, Phyllanthus niruri, Tinospora cordifolia and Tribulus terrestris were screened in vitro for antibacterial activity by cup diffusion method against eleven human pathogenic bacteria. Caesalpinia coriaria (Jacq.) Willd. (Caesalpinaceae) recorded significant antibacterial activity against all the test bacteria. The Minimal Inhibitory concentration (MIC) value of the aqueous extract of leaves and pod of C. coriaria for the test bacteria ranged between 2 to 10 mg/ml and 0.5 to 4 mg/ml, respectively. Similarly the MIC value of the methanol extracts of leaves and pod of C. coriaria for the test bacteria varied between 0.5to 4 mg/ml and 0.5 to 4 mg/ml, respectively depending on the bacterial species. Phytochemical analysis of leaf and pod materials revealed that the antibacterial activity is due to presence of acidic and phenolic fractions. Further separation of active fraction resulted in the loss of antibacterial activity, indicating a synergistic effect of the isolated active fraction. Comparison of the inhibitory activity with the antibiotics Gentamicin and Streptomycin revealed that methanol extract of both leaf and pod and aqueous pod extracts were significantly higher than that of the antibiotics tested. The results suggest that C. coriaria is a potential candidate plant for further exploitation in medical microbiology.