In vitro killing rate of Euphorbia heterophylla and Pterocarpus lucens extracts minimum bactericidal concentration (MBC) on some clinical bacterial isolates

Abstract

In vitro antibacterial activity of methanol and ethanol leaf extracts of Euphorbia heterophylla and Pterocarpus lucens were investigated against six bacterial clinical isolates using the tube dilution and agar diffusion methods. Salmonella typhi was the most susceptible to methanol leaf extracts of E. heterophylla with a zone of inhibition ranging from 16 to 24 mm for 12.5 to 100 mg/ml concentration. This was followed by Streptococcus lactis, Escherichia coli, Staphylococcus aureus, and Shigella species in that order with Proteus vulgaris not susceptible to the different test concentrations of both plant extracts. E. heterophylla had the least minimum inhibitory concentration (MIC) of 6.25 mg/ml against E. coli and S. typhi while P. lucens extract MIC of 25.00 mg/ml was the least against S. typhi. Since there is an inverse relationship between MIC value and susceptibility of the clinical test isolates, the MIC values also shows that E. heterophylla methanol leaf extracts were more potent to the susceptible test organisms having lower MIC values than the corresponding ethanol leaf extract MIC value. E. heterophylla extract minimum bactericidal concentration (MBC) was 25.00 mg/ml for the sensitive isolates except for methanol extract with 12.50 mg/ml against S. typhi and ethanol extract with 12.50 mg/ml against S. aureus. P. lucens extract MBC was 100.00 mg/ml for the sensitive test isolates except for ethanol leaf extracts with 50.00 mg/ml against S. typhi. The killing rate of E. heterophylla methanol leaf extract MBC shows that E. coli was most rapidly killed at a rate of 4.53x106 CFU/min with S. aureus as the least killed at a rate of 0.62x10 6 CFU/min. S. lactis and E. coli were the most rapidly killed by P. lucens leaf extract MBC at a rate of 1.90x10 6 CFU/min. The killing rate of the extracts showed a positive support in the potential use of these plants in curing some infections as done by the traditional herbal healers in Anyigba, Kogi State, Nigeria.