Antimicrobial activity of cowpea (Vigna unguiculata) leaf extracts

Cowpea (Vigna unguiculata (L.) Walp), an indigenous African legume crop, is used to treat epilepsy, bilharzia, chest pains and constipation. Acetone and ethanol extracts of the leaves of Bechwana White (BW) and Kpodjiguégué (Kpod) cultivars were investigated for their antimicrobial properties against bacterial and fungal pathogens. With the exception of Fusarium equiseti, all the extracts significantly inhibited growth of the fungal pathogens at 5.0mg ml− 1. Alternaria alternata was significantly reduced by both BW extracts at 2.5mg ml− 1 whereas only the ethanol extract showed antifungal activity against Fusarium proliferatum at the same concentration. The acetone extract from Kpod significantly inhibited the growth of A. alternata at 2.5mg ml− 1. The acetone and ethanol extracts showed no inhibitory activity at 1.0mg ml− 1. BW acetone extracts inhibited growth of the Gram-positive bacteria, Staphylococcus aureus and Enterococcus faecalis, at 2.5mg ml− 1 and Bacillus cereus, B. subtilis and Enterobacter cloacae at 5.0mg ml− 1. Ethanol extracts of the same cultivar only showed antibacterial activity against Enterococcus faecalis and Enterobacter cloacae at 5.0mg ml− 1. The Kpod extracts exhibited no inhibitory effect on the bacteria. This is the first report on the inhibitory effect of cowpea leaf extracts on the growth of bacterial and fungal pathogens.