In vitro Antimicrobial Activities of Crude Extracts of Vernonia amygdalina and Croton macrostachyus against Some Bacterial and Fungal Test Pathogens

Abstract

The aim of the present study was to investigate the antibacterial and antifungal activities of crude extracts of Vernonia amygdalina 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). 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 two plant extracts against the same pathogens was determined using the broth dilution method. Chloroamphenicol was used as positive control for for bacterial pathogen and Tilt was also used as positive controls fungal pathogens. Meanwhile Dimethyl Sulfoxide was taken as a negative control for both. 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 V. amygdalina (4.58±0.27). All the methanolic and ethanolic crude extracts had the highest growth inhibitory effects as compared with the water crude extracts on all bacterial pathogens. The methanol crude extract of C. macrostachyus had highest zone of inhibition (21±0.29 mm) against S. aureus, with a minimum inhibitory concentration of 25mg/ml. Similarly, the ethanol crude extract of C. macrostachyus had shown highest antifungal activity against A. niger with inhibition zone of 15.5±0.29. The results indicate the potential of these medicinal plants in treating some bacterial and fungal infection. Thus, further detailed studies are recommended to be carried out to characterize their bioactive compounds for development of new effective antimicrobial drugs.