Abstract

In this study, the ethanol extract (EE), ethyl acetate extract (EAE), aqueous decoction extract (ADE) and aqueous maceration extract (AME) of Vernonia amygdalina leaves were subjected to total phenolic (TP) and total saponin (TS) content determination, in vitro radical scavenging activity and antimicrobial susceptibility testing (AST). The TP contents in order of decreasing quantities were 63.044, 38.834, 53.148 and 39.391 mg of gallic acid equivalents (GAE) per g dry extract for EE, EAE, ADE and AME, respectively. The TS assay revealed that the EAE extract possessed the highest TS content with a value of 952.037 mg of diosgenin equivalents (DE) per g dry extract. This was followed by the EE, ADE and AME extract with TS content of 841.370, 159.741 and 118.444 mg diosgenin equivalents (DE) per gram dry extract. The DPPH assay revealed that the ADE had the highest DPPH radical scavenging activity with an IC50 value of 501.207 µg/ml. This was followed by EE, EAE and AME with IC50 values of 636.010, 658.277 and 1368.929 µg/ml, respectively. The ADE also exhibited the highest ABTS radical scavenging activity with an IC50 value of 3195.083 µg/ml. In the subsequent order of decreasing ABTS scavenging activity was AME, EE and EAE extracts with IC50 values of 4142.156, 5508.517 and 6547.940 µg/ml. The results of AST showed that the test organisms E. coli O157:H7 and Y. enterocolitica were resistant towards the V. amygdalina extracts tested. Only the AME extract possesses a MIC value of 31.25 mg/ml against Y. enterocolitica. The data obtained reaffirms V. amygdalina’ spontential as a source of dietary antioxidants and provides information on the the suitability of V. amygdalina against E. c.oli O157:H7 and Y. enterocolitica.