Abstract

Leaves of seventeen medicinal plants used inter alia to treat infections were collected from Phalaborwa, Limpopo Province, South Africa. Plant species used in this investigation wereTerminalia sericea, Diospyros mespiliformis, Cordia grandicalyx, Fluggea virosa, Cassia abbreviata, Colophospermum mopane, Xanthorcesis zambesiaca, Dichrostachys cineria,Helinus integrifolius, Schotia brachypetala, Berchemia discolor, Bridelia mollis, Psidium guavaja and Vangueria infausta. The antibacterial activity of acetone leaf extracts was determined against twenty different bacterial species using a serial microplate dilution method to determine the minimal inhibitory concentrations (MIC). C. abbreviata and X. zambesiaca had the highest activity against both groups of bacteria with overall average MIC values of 0.113 and 0.285 mg/ml, respectively, while C. grandicalyx had poor inhibition against both Gram positive and Gram negative bacteria (overall MIC value of 1.677 mg/ml). Judging from average MIC values (mg/ml), it would appear that all extracts save C. abbreviata had better activity against Gram positive bacteria than Gram negative bacteria.V. infausta, D. mespiliformis, F. virosa and T. sericea had good activity against Gram positive bacteria. Judging from average MIC values, it would seem that K. oxytoca was the most sensitive bacterium to plant extracts, while P. mirabilis was the most resistant. Someof these plant species are used to treat ailments associated with one or another form of infection. These finding suggests that extracts of these plants exert their medicinal actions through inhibition of growth of the pathogen.

Key words: Antibacterial activity, minimal inhibitory concentration, total activity, Cassia abbreviate.