Title : Combined antibacterial effect of croton macrostachyus, calpurina aurea and ocimum gratissimum against selected clinical and standard pathogenic bacteria
Background: The use of medicinal plants as treatment options of human and animal diseases can be traced back in human history, and about ten percent of identified medicinal plants serve a pharmaceutical role because they have active chemical constituents such phenolic acids, flavonoids, tannins and lignin. Ethiopia is a place rich in medicinal plants, though most studies in the region have only considered the individual effects of their extracts while under-exploring their combined effects.
Objective: The objective of this 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 against standard and clinical isolates of Staphylococcus aureus, Escherichia coli and Salmonella typhi by using methanol, acetone and chloroform as solvents. Methods: Extracts were prepared at a plant-to-solvent ratio of 50 g to 500 mL and then set to a concentration of 50 mg/mL by dissolving 100 mg of crude extract in 2 ml of 10% dimethyl sulfoxide in small cups, from which 100 µL was used for antibacterial assays using the disc diffusion method. Minimum inhibitory and bactericidal concentration assays were assessed with the broth microdilution and overnight bacterial culture preparation techniques, respectively. The fractional inhibitory concentration index was used for synergistic activity analysis.
Results: Combinations of extracts showed relatively better effects against most test bacteria with inhibition zones reaching up to 23.00 ± 1.00 mm (Salmonella typhi) despite limited activity on both standard and clinical isolates of Escherichia coli. The lowermost minimum inhibitory and bactericidal concentrations were 3.125 mg/mL and 6.25 mg/mL, respectively, and a few synergistic and many additive effects were recorded for different forms of combinations on different bacterial isolates.
Conclusion: The combined use of extracts is relatively promising, though further work is required to clearly set the safety margins of combinations used in vivo, as this is the first report on all settings used here. The findings of this study provide scientific evidence for communities, pharmaceutical industries, and other concerned bodies regarding alternative formulations of phytochemicals for the relief of different physiological deviations, with the combined use of plants showing better performance.