www.ajethno.com American Journal of Ethnomedicine, 2014, Vol. 1, No. 1, 064-071 Available online at http://www.ajethno.com © American Journal of Ethnomedicine Antibacterial Activities of the Leaf and Bark Extract of Persea americana Ogundare A. O. and Oladejo B. O.* Department of Microbiology, Federal University of Technology, P.M.B. 704, Akure, Nigeria ABSTRACT The antibacterial activities of the methanolic leaf and bark extract of Persea americana was tested in vitro on bacterial isolates namely: Streptococcus pyogenes, Proteus mirabilis, Salmonella typhi, Klebsiella pneumoniae, Escherichia coli, Bacillus subtilis (NCIB 3610), Staphylococcus aureus (NCIB 8588), Escherichia coli (NCIB 86), Klebsiella pneumoniae (NCIB 418) and Pseudomonas aeruginosa (NCIB 950), using the agar well diffusion method. The leaf extract was able to inhibit the growth of the test organisms at a concentration of 50.0mg/ml except Escherichia coli, Salmonella typhi, Proteus mirabilis and Escherichia coli (NCIB 86), while the bark extract at the same concentration inhibited the test organisms except Salmonella typhi, Escherichia coli, Bacillus subtilis (NCIB 3610) and Escherichia coli (NCIB 86). The highest zone of inhibition of 6.0 mm and 12.0 mm was observed on Staphylococcus aureus (NCIB 8588) for the leaf and bark extract respectively, while the least zone of inhibition was observed on Klebsiella pneumoniae (2.0 mm) for leaf extract and Proteus mirabilis (3.0 mm) for bark extract. The Minimum Inhibitory Concentration (MIC) of the leaf extract ranged from 10.0 to 30.0 mg/ml and 5.0 to 30.0 mg/ml for the bark extract. The antibacterial activity of the methanolic plant extract inhibited the growth of the test isolates as much as that of the commercial antibiotics. There was a decrease in the bacterial count as the exposure time to the extract increased in the rate of killing of the plant extracts on the isolates. Phytochemicals such as saponins, tannins, flavonoids and terpenoids were observed to be common to both extracts. The bark extract exhibited a higher antibacterial activity as compared to the leaf extract. Keywords- Antibacterial, Zone of inhibition, Agar well diffusion, Phytochemicals and Rate of killing.