The emergence of antibiotic resistance as well as the recent undesirable side effect of some of the commercially available antibiotics has led to the screening of plant extract in order to discover new drug that could serve as alternative therapy for the treatment of various infections and diseases. Fresh leaf of Ocimum gratissimum (scent leaf) sample was collected, air-dried at room temperature and blended to powder using electric blender. The extraction was done using reflux extraction method and methanol as solvent. The phytochemical analysis and the antibacterial activity of O. gratissimum were determined to ascertain the different phytochemicals present in the plant extract. The extract was also tested against some selected Gram negative intestinal pathogenic bacteria; Escherichia coli, Shigella and Salmonella species, by reconstituting the extract in dimethyl sulphoxide (DMSO) to obtain different concentration (0.2, 0.1, 0.05 and 0.025 g/ml) and agar well diffusion techniques were used to evaluate the antibacterial susceptibility of the leaf extract. The qualitative phytochemical analysis of the extract revealed the presence of alkaloid, anthraquinone, flavonoid, glycoside, phenol, saponin, steroid and tannins. The result of antibacterial analysis showed that the extract of O. gratissimum has antibacterial activity against E. coli. This could be as a result of the presence of various phytochemicals or the interaction of one or more of the identified metabolites against the test organisms. However, there was no zone of inhibition (antibacterial effect) recorded on Salmonella and Shigella spp. as they were resistant to the extract. The results obtained from this research, suggest that Escherichia coli was susceptible to the leaf extract and the plant could be used as potential source of natural product for the treatment of infection.
Key words: Antibacterial activity, scent leaf, gastrointestinal bacteria, phytochemicals, plant extract.