Vol. 8(2), pp. 211-216, 8 January, 2014 DOI: 10.5897/AJMR2013.6390 ISSN 1996-0808 ©2014 Academic Journals http://www.academicjournals.org/AJMR African Journal of Microbiology Research Full Length Research Paper Antibacterial activity of the stem bark extracts of Acacia mearnsii De Wild Mbolekwa B. N. 1 , Kambizi L. 2 , Songca S. P. 3 * and Oluwafemi O. S. 4 1 Department of Botany, Walter Sisulu University, Private Bag X1, Mthatha, 5099, Eastern Cape, South Africa. 2 Department of Horticulture, Cape Peninsula University of Technology, PO Box 652, Cape Town, 8000, Western Cape, South Africa. 3 Faculty of Science, Engineering and Technology, Walter Sisulu University, PO Box 19712, Tecoma, East London, 5214, Eastern Cape, South Africa. 4 Department of Chemistry, Cape Peninsula University of Technology, PO Box 652, Cape Town, 8000, Western Cape, South Africa. Accepted 25 November, 2013 Antibacterial activity of four different extracts from the stem bark of Acacia mearnsii was measured against five Gram-positive and five Gram-negative bacterial strains: Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Micrococcus kristinae, Streptococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, Shigella flexneri, Klebsiella pneumonia and Serratia marcescens. The extracts assessed include hexane, ethyl acetate, dichloromethane and methanol. The hexane, ethyl acetate and methanol extracts showed some inhibitory effects on the selected bacteria. The hexane extract showed some activity against four Gram-positive and two Gram-negative bacterial strains, but was not active against one Gram-positive and three Gram-negative bacterial strains. The ethyl acetate extract was effective against all the bacterial strains used in this study. The methanolic extract was effective against all the Gram-positive bacterial strains but it was not active against the Gram-negative bacterial strains except Escherichia coli. The dichloromethane extract was not active at all against all the bacterial strains tested. Key words: Acacia mearnsii, antibacterial activity, bacteria species. INTRODUCTION Globally, the attractions that have led to the study of medicinal plants as a basis of pharmacologically active compounds have improved and have become greater than ever before. In some developing countries, it is acknowledged that plants are the main medicinal sources to treat infectious diseases. The human environment in these countries is crowded while sanitation is poor; therefore diseases like diarrhoea and dysentery which are caused by bacterial enteropathogens are among the core causes of morbidity and death (Alanis et al., 2005). Plants still make an input that is very important to health care, even though there is great progress in modern medicine. The reason for this is the growing appreciation of the value of traditional medical systems, mainly of Asian origin, and the recognition of medicinal plants from the native pharmacopoeias, which have important healing power (Adebolu and Oladimeji, 2005). A lot of work has been done on antimicrobial and phytochemical constituents of medicinal plants and utilizing them for the management of microbial infections for both topical and systemic applications as likely alternatives to formally approved chemically artificial drugs to which many infectious microorganisms have become resistant (Akinpelu and Onakoya 2006). National *Corresponding author. E-mail: spsongca@wsu.ac.za.