Natural substances with medicinal properties have been isolated from several plants and are advocated for use as antimicrobials. This study was aimed at evaluating the antibacterial activities of ethanolic leaf extracts of four plants against selected bacterial species. The plants examined were Helianthus annuus, Moringa oleifera, Euphorbia heterophylla and Physalis angulata while the bacterial species were Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis, Escherichia coli, Klebsiella sp. The minimum inhibitory concentration of the extracts was carried out, using the agar diffusion method while the growth profiles of the test bacterial species were carried out in broth media. The plant extracts were observed to contain phenol, terpenoids, saponins and tannins as phytochemical constituents. All the extracts showed inhibition against most of the test bacteria, although the degree of inhibition was observed to be directly proportional to the concentration used. However, Klebsiella sp was recorded to show resistance to most concentrations of the extracts with resistance to all concentrations of the Physialis angulata. The minimum inhibitory concentration (MIC) of all the extracts against Staphylococcus aureus and Bacillus subtilis was observed to be 500 mg/L. For Pseudomonas aeruginosa, MIC of 500 and 2000 mg/L were observed for Physalis angulata and Euphorbia heterophylla, respectively while 1000 mg/L was observed for the Helianthus annuus and Moringa oleifera. In presence of the extracts, extended lag period was observed during growth, when compared to the control broth culture. In some cases, growth was not evident in the broth cultures containing the extracts throughout the period of incubation. The findings of this study could help in the development of advanced products that can be of medical and pharmaceutical importance.
