ANTIMICROBIAL ACTIVITIES OF CRUDE EXTRACTS OF SELECTED MEDICINAL PLANTS AGAINST SOME BACTERIAL AND FUNGAL TEST PATHOGENS

Abstract

Traditional medicinal plants have several uses in different parts of the world. In Ethiopia, it remains the main source of treatment for the majority of the population and its livestock. The aim of this study was to assess the antibacterial and antifungal activities of crude extracts of Solanum incanum, Vernonia amygdalina, Datura stramonium L., and Croton macrostachyus against four bacterial pathogenic species (i.e. Staphylococcus aureus, Streptococcus agalactiae, Salmonella Typhi, Escherichia coli) and two fungal pathogenic species (i.e. Aspergillus flavus and Aspergillus niger). The roots of Solanum incanum and leaves of Vernonia amygdalina, Datura stramonium L., and Croton macrostachyus were shade dried and ground to powders and the crude extracts were prepared using absolute ethanol, methanol (99.8%) and distilled water. Antimicrobial activities of the resulting extracts were determined by measuring zone of inhibitions on cultures of six selected pathogens using the disc diffusion method. The minimum inhibitory concentration (MIC) of the plant extracts against the same pathogens was determined using the broth dilution method. Chloroamphenicol and Tilt were used as positive controls for bacterial and fungal pathogens, respectively, while Dimethyl Sulfoxide was used as a negative control for both. The results showed that the highest percentage yield was recorded for methanol extract of V. amygdalina (14.89±0.25%) and the lowest yield was observed for the water extract of S. incanum (4.33±0.176 %). All the methanolic and ethanolic crude extracts, with the exception of the methanolic crude extract of D. stramonium, had the highest growth inhibitory effects as compared with the water crude extracts on all bacterial pathogens. However, the three solvent crude extracts had less antimicrobial activities than the standard antibiotics. The methanol crude extract of S. incanum had highest zone of inhibition (22±1.15 mm) against S. agalactiae with a minimum inhibitory concentration of 25mg/ml. Whereas, the methanolic crude extract of C. macrostachyus had relatively a lower zone of inhibition (4.0±0.0 mm) against E. coli with a minimum inhibitory concentration of 100mg/ml. Similarly, the methanol crude extract of S. incanum had shown significant antifungal activity against A. niger with inhibition zone of 25.13±0.4mm and a minimum inhibitory concentration of 125mg/ml. In contrast, the methanol crude extract of C. macrostachyus had a low antifungal activity (9.56±0.23 mm) against A.niger with a minimum inhibitory concentration of 500mg/ml. In conclusion, the results indicate the potential of these medicinal plants in treating some bacterial and fungal infection. Thus on the basis of these clues, further detailed studies are recommended to be carried out in the tested plant to identify and characterize their bioactive compounds which are necessary for the development of new and more effective antimicrobial drugs.