Master's Thesis from the year 2019 in the subject Biology - Micro- and Molecular Biology, grade: 4, Arba Minch University, course: Medical Microbiology, language: English, abstract: The aim of this study was to determine the antibacterial activity of crude extracts of four medicinal plants (A. pirottae, G. schweinfurthii, K. begoniifolia, and U. leptocladon), against ATCC and MDR clinical isolates of bacteria. Based on ethnobotanical data, four plants were collected from different areas of South Omo through several field trips followed by taxonomic identification. Leaves (A. pirottae, K. begoniifolia, and U. leptocladon) and root (G. schweinfurthii) parts of plants specimens were subjected to extraction process using six different organic solvents through maceration and subsequent filtration. The resultant crude extracts were screened for primary in vitro antibacterial activity against ATCC bacterial strains, using agar well diffusion assay. The plants that showed the highest activity indices were further screened against MDR bacterial isolates. MIC was performed on the most active plant extract. Results of antibacterial activities were analyzed using statistical software, SPSS for Windows version 20. The antibacterial activity significantly varied among the plant species, type of solvents used for the extraction and strains of bacteria tested. Ethyl acetate and ethanol was highly effective for extracting antibacterial principles, irrespective of plant species. The results of primary screening revealed that two plants (K. begoniifolia, and U. leptocladon) were highly active against ATCC strains. The results of the extended screening showed that, among the two plants, ethyl acetate extract of U. leptocladon efficiently inhibited the growth of MDR bacterial isolates. The MIC values of U. leptocladon were varied in inhibiting MDR bacteria tested. The overall findings of this study demonstrated that all the four plants have antibacterial activities in varying degrees. U. leptocladon showed the widest and highest spectrum of antibacterial activities as per agar well diffusion assay and analysis of MIC. However, further ongoing and in-depth studies are mandatory in order to prove and understand in vivo efficacy, mechanism of action and toxicological profile of these plants. In many regions of the world, particularly Ethiopia, the vast majority of traditional medicines are plant based. However, these plants were neglected and scarcely explored. Therefore, screening of plants used in traditional medicine could provide the chance of discovering antimicrobials that fight against infectious diseases.