Bitew, Adane (PhD, Associate Professor)Abebe, Abiy2018-10-302023-11-062018-10-302023-11-062018-06http://etd.aau.edu.et/handle/123456789/13405Background: Cognizant of the fact that, there has been an alarming increase in the incidences of infectious diseases, emerging and re-emerging antibiotic resistance organisms; there is an urgent need of novel antimicrobial compounds with new mode of action, effective and inexpensive. One potential source for the search of such agent is medicinal plants due to the presence of wide range secondary metabolites in their tissue. Objectives: The aim of this study was to investigate the antimicrobial activity of 12 traditionally used Ethiopian medicinal plants for their potency, spectrum of antibacterial, antifungal activity and acute toxicity. Methods: Ethnobotanical literature survey was conducted to select 12 medicinal plants. Antimicrobial activities of 80% Ethanol extracts of all plants were investigated by agar well diffusion techniques against 22 organisms. Agar dilution techniques were employed to determine the Minimum Inhibitory, Bactericidal and Fungicidal Concentrations. The Oral acute toxicity study was determined on the most active plant extract B. abyssinica. Results: Among investigated medicinal plants, B. abyssinica, X. strumarium, R. natalensis, Z. scabra, E. cymosa, C. abyssinica and S. abyssinica, showed strong antibacterial activity with inhibition zone ranging from 9-27 mm; while, B. abyssinica (42 mm) and X. strumarium (48 mm) showed strong antifungal activity. The extracts of B. abyssinica showed most potent antimicrobial activity with MIC value ranging 0.250-16 mg/ml. Staphylococcus aureus was the most sensitive organism against B. abyssinica with MIC value of 0.25 mg/ml. Nevertheless, K. pneumoniae and Citrobacter species were the least sensitive bacteria with 16 mg/ml MIC and MBC value. T. mentagrophytes and T. rubrum were the most susceptible fungal organism to the treatment of B. abyssinica, X. strumarium while, A. niger was the most resistant fungus. The LD 50 of B. abyssinica was found to be 4103.175 mg/kg. Conclusion: The majority of the plants tested showed promising antibacterial and antifungal potency, especially on gram positive bacteria and dermatophytes. Further studies are recommended to explore in-vivo efficacy, mechanism of action and toxicological studies of the most promising plant.en-USAntibacterial, Antifungal, Medicinal Plant, B. abyssinica, MIC, Acute ToxicityThesis