Phytochemical screening and antibacterial activities of Vernonia ambigua, Vernonia blumeoides and Vernonia oocephala (Asteraceae)

Some Vernonia species (Vernonia ambigua, Vernonia blumeoides and Vernonia oocephala) used in Northern Nigerian traditional medicine, were subjected to phytochemical screening using standard procedures. The antibacterial activity using the disc diffusion method as outlined by the NCCLS was carried out on Klebsiella pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Corynbacterium ulcerans, methicillin resistant Staphylococcus aureus (MRSA), Salmonella typhi, Pseudomonas aeruginosa, Shigella dysentriae, Proteus mirabilis and Pseudomonas fluorescence. The results of the antibacterial activity as indicated by zone of growth inhibition ranged from 14 to 27 mm for the crude ethanol extracts and chloroform fractions of the Vernonia species being studied. The activity of chloroform fraction of V. blumeoides was higher on C. ulcerans and K. pneumoniae (27 mm), while the chloroform fractions of V. oocephala and V. ambigua were more active on P. mirabilis (27 mm) and S. typhi (22 mm), respectively. It is worth of mention that the chloroform fractions of the three Vernonia species demonstrated activity (20 mm) against MRSA. The minimum inhibitory concentration (MIC) values ranged from 1.25-2.5 mg/mL for all the organisms tested. The MIC of 1.25 mg/mL exhibited by the chloroform fractions on both Gram positive and negative bacteria indicates broad spectrumactivity of the Vernonia species being studied. Phytochemical screening of the extracts/fractions revealed the presence of steroids/terpenes, saponins, flavonoids, alkaloids, tannins and glycosides. The antibacterial activity exhibited in this study may be attributed to flavonoids, saponinss or sesquiterpene lactones. The overall results indicate that the extracts/fractions are potent antibacterial preparations at least in vitro. This lends credence to the use of these plants for the treatment of various infectious diseases.