Abstract:
Medicinal plants, as treatment options of human and animal diseases, are traced back to
human history in their use and about ten percent of them ever identified serve a
pharmaceutical role as they have active chemical constituents of phenolic acids, flavonoids,
tannins and lignin. Ethiopia is reported to be rich habitat of them with most studies
conducted on the individual effects of extracts leaving their combined effects less
concerned. So, the objective of this experimental research was to assess the synergistic
antibacterial activity of crude extracts of leaves of Croton macrostachyus, Calpurnia aurea
and Ocimum gratissimum collected from Bahir Dar town on standard and clinical isolates
of Staphylococcus aureus, Escherichia coli and Salmonella typhi by using methanol,
acetone and chloroform as solvents. Extracts prepared in plant to solvent ratio of 50 g to
500 ml were made into a concentration of 50 mg/ml by dissolving 100mg of crude extract
in 2ml of 50% DMSO in small cups, from which 100 µl of it was used for antibacterial
assay using disc diffusion method. Minimum inhibitory and bactericidal concentration
assays were assessed by broth micro dilution and overnight bacterial culture preparation
techniques respectively. The fractional inhibitory concentration index was used for
synergistic activity analysis. Combinations of extracts showed relatively better effect
against most test bacteria with inhibition zone inclining up to 23.00 ± 1.00 (Salmonella
typhi) despite of limited activity both on standard and clinical isolates of Escherichia coli.
The lowermost minimum inhibitory and bactericidal concentrations of 3.125 mg/ml and
6.25 mg/ml respectively and few synergistic and many additive effects were recorded for
different forms of combinations on different bacterial isolates. As a result, combined use
of extracts is relatively promising though it requires further work to clearly set safety
margins of combinations in in-vivo as this was the first report with all settings used here.
The finding may add a scientific evidence for community, pharmaceutical industries and
other concerned bodies about alternative formulations of phytochemicals for relief of
different physiological deviations with combined use of plants found better performing
