Abstract:
Plants have been used for generations as source of medicine in the treatment of a variety of
human illnesses. In Ethiopia, many plants are used for this purpose by traditional healers
without any scientific justification for their therapeutic values. Thus, this study was aimed atassessing the antibacterial activities of crude extracts obtained from different parts of Calotropis
procera and Vernonia amygdalina against Escherichia coli, Staphylococcus aureus, and
Pseudomonas aeruginosa. The stems, roots and leaves of the selected plant species were shade
dried and ground to powders and the bioactive components were extracted using ethanol
(99.5%), methanol (99.8%), hexane (99.8%) and distilled water. The antibacterial activities of
the resulting extracts against the three selected pathogens were evaluated using the paper disc
method and the inhibitory zones were recorded in millimeters. Minimum inhibitory
concentrations (MICs) of the plant extracts against Escherichia coli, Staphylococcus aureus
and Pseudomonas aeruginosa were assessed using the agar dilution method. Chloramphenicol
and sterile distilled water were used as positive and negative controls, respectively. The bioassay
studies of the crude extracts were undertaken at five different concentrations (20, 30, 40, 50 and
60 mg/ml). The results revealed that the crude extracts of ethanol, methanol, hexane and water
had antibacterial activities on all three bacterial species except at 20 mg/ml of all solvent
extracts. Methanol and ethanol extracts had the highest growth inhibitory effects as compared
with those of the aqueous and hexane crude extracts. However, the four solvent crude extracts
had less antibacterial activities than chloramephenicol. S. aureus was found to be the most
susceptible pathogen to the crude ethanol (99.5%) and methanol (99.8) extracts of the leaves of
Vernonia amygdalina (22 mg/ml) and ethanol extract of the leaves of Calotropis procera (22
mg/ml). Whereas Pseudomonas auruginosa was the least susceptible bacterium to crude ethanol
extract (99.5%) of the root of Calotropis procera at 28 mg/ml and crude water extract of the root of Vernonia amygdalina at 28 mg/ml. The growth inhibitory activities of the crude extracts were
found to be significantly different for the four concentrations (30, 40, 50 and 60mg/ml) in both
plant parts (p < 0.05).
