Antibacterial activity of Plectranthus cyaneus leaf extracts on Escherichia coli and Staphylococcus aureus

Abstract

Drug resistance of pathogenic microorganisms is becoming an increasing problem to human health. In order to find alternative therapy against these drug resistant pathogens, there is need to screen natural herbs that have historically been used for treatment hence the aim of this study is to determine the antibacterial activity of Plectranthus cyaneus on E. coli and S. aureus.During this study, aqueous and methanolic leaf extracts of Plectranthus cyaneus were used and the phytochemical profile of these extracts was determined. Thereafter, the activity of the extracts was assessed on two pathogenic microorganisms i.e., E. coli and S. aureus and three methods were used during the study, that is,(a) the agar gel well diffusion assay for antibacterial susceptibility, (b) the Minimum Inhibitory Concentration Determination and (c) the Minimum Bactericidal Concentration determination.The phytochemicals detected were;saponins (+++),tannins(++), flavonoids, alkaloids, phenolic compounds and cardiac glycosides (+). S. aureus was susceptible to the extracts with mean diameters of25.5±2.121mm for aqueous extracts and 19±0.000mm for methanolic extracts whereas E. coli was resistant to both aqueous and methanolic extracts.The mean minimum inhibitory concentrations for S. aureus were 1.953±0E-7mg/ml and 2.929±1.381mg/ml for aqueous and methanolic extracts respectively. Also, the minimum bactericidal concentrations for S. aureus were 11.791±5.523mg/ml for aqueous extract and 4.883±4.143mg/ml for methanolic extract meaning that the drug should be admitted in those concentrations to be able to inhibit or kill S. aureus respectively. This study suggests that Plectranthus cyaneus leaf extracts has potential for treatment of wounds caused by S. aureus. MIC and MBC results showed no statistical significance when the activity of the two solvents was compared (p>0.05),so both solvents don’t give similar results meaning Plectranthus cyaneus is more effective with one solvent than the other.