RESUMEN
This study was carried out to evaluate the antibacterial activity of Ocimum gratissimum and Vernonia amygdalina on selected bacterial species, as well as comparing the antibacterial activities of their fresh and dried leaves. Fresh leave samples of the plants were collected from Okwu, Uratta in Owerri North, Imo State, Nigeria. The plants were identified and ethanolic and aqueous extractions of the dried and fresh leave samples were done using standard procedures. Antibacterial activity of the extracts was tested invitro against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Streptococcus pyogenes using agar diffusion, punch method. The pattern of inhibition varied with plant extract, solvent used for extraction and test organisms. For the dried leave samples, all the extracts showed zones of inhibition above 5mm diameter against all the isolates, except hot water extract which had no activity for all. Ethanol extracts showed the highest zone of 20mm of O. gratissimum against Staphylococcus aureus and highest zone of 40mm by V. amygdalina against Pseudomonas aeruginosa. However, for the fresh leave samples, only Ethanolic extract of O. gratissimum was active against all the isolates. None of the fresh leave sample extracts of V. amygdalina was active against all the isolates, except the cold water extract which showed zones of inhibition of 10mm against E. coli and Streptococcus pyogenes each. It was also observed that Staphylococcus aureus had the lowest Minimum Inhibitory Concentration (MIC) of 0.48μg/ml and 0.82μg/ml against O. gratissimum and V. amygdalina respectively, and Minimum Bactericidal Concentration (MBC) of 0.28μg/ml and 0.61μg/ml respectively. From this work, it has been noted that the leaves of Ocimum gratissimum and Vernonia amygdalina have antibacterial properties. Government is therefore advised to invest money into more pharmacological researches on these extracts in order to make them better alternative to modern medicine for the treatment of infection caused by these pathogens.