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.