Phytochemical Screening and in-vitro Evaluation of Antibacterial Activities of Echinops amplexicaulis, Ruta chalepensis and Salix subserrata Against Selected Pathogenic Bacterial Strains in West Shewa Zone, Ethiopia

Background Although traditional healers in Ethiopia have a long history of using medicinal plants to treat diseases in animals and humans, studies on the antibacterial activities and potential bioactive ingredients of most medicinal plants have been insufficient. Therefore, this study aimed to evaluate the in-vitro antibacterial activities and to screen phytochemical constituents of selected medicinal plants against reference bacterial strains. Methods The fresh and healthy roots of Echinops amplexicaulis, fruits of Ruta chalepensis, and leaves of Salix subserrata were collected from West Shewa Zone, Ethiopia. Agar well diffusion and agar dilution methods were used to evaluate antibacterial activities and minimum inhibitory concentrations (MIC). All the crude plant extracts were tested against Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli and Pseudomonas aeruginosa at concentrations of 100, 50, and 25 mg/mL in each triplet (3x). MIC of crude extracts ranging from 1.5625 to 12.50 mg/mL was applied to all bacterial strains. The positive control was ciprofloxacin disk (5 μg) and the negative control was 5% dimethyl sulfoxide. The presence of secondary metabolites of each crude extract was screened. The group means comparisons were done using one-way ANOVA and results were presented as mean ± standard deviation. Results Although all selected plant extracts had shown antibacterial activities, methanol extracts had a greater zone of inhibition against all reference bacterial strains when compared to petroleum ether extracts. The growth of P. aeruginosa was inhibited at a minimum concentration of both methanol and petroleum extracts (1.5625 mg/mL) when compared to the remaining bacterial strains. Phytochemical screening showed that saponins and alkaloids were found in all crude plant extracts, while phytosterol was meager. Conclusion This study revealed that all tested plants had significant secondary metabolites and antibacterial activities against reference bacterial strains.