Shibeshi, Workineh(PhD)Nedi, Teshome (PhD)Molla, Yalew2018-06-272023-11-062018-06-272023-11-062015-11http://etd.aau.edu.et/handle/123456789/4255Infectious diseases are the critical problems of the world as a result of the emergence of different antimicrobial resistant microorganisms. Medicinal plants play great roles in the treatment of various infectious diseases. Rhamnus prinoides is one of the the medicinal plants used traditionally for treatment of bacterial infections. The antibacterial activity of the crude extract of the plant had been shown by a previous study, but this study was undertaken to further the claimed medicinal use of the plant by screening its solvent fractions for the said activity so that it could serve as a basis for subsequent studies. The solvent fractions of the plant were obtained by successive soxhlet extraction with solvents of increasing polarity, with chloroform and methanol, followed by maceration of the marc of methanol fraction with water. The antibacterial activity of the solvent fractions was evaluated on seven bacterial species using agar well diffusion method at different concentrations (780 mg/ml, 390 mg/ml and 195 mg/ml) in the presence of positive control and negative control. The minimum inhibitory concentration of the solvent fractions was determined by micro-broth dilution method using resazurin as indicator. Methanol and chloroform fractions revealed antibacterial activities against the growth of test bacterial strains with varying antibacterial spectrum and the susceptible bacterial species were Staphylococcus aureus, Streptococcus pyogen, Streptococcus pneumoniae and Salmonella typhi. The strains of Pseudomonas aeruginosa and Escherichia coli were iv not sensitive to chloroform fraction. The average minimum inhibitory concentration value of the methanol and chloroform fractions ranged from 8.13 mg/ml to 32.5 mg/ml and from 8.13 mg/ml to 16.25 mg/ml, respectively. In conclusion, the methanol and chloroform fractions demonstrated significant antibacterial activities against the growth of pathogenic bacteria unlike the aqueous fraction. Key words: Antibacterial activity, agar well diffusion, minimum inhibitory Concentration, Staphylococcus aureus, Streptococcus pyogen, Streptococcus pneumoniae, Salmonella typhi Pseudomonas aeruginosa, Escherichia colienAntibacterial activityAgar well diffusionThesis