Antibacterial activity of selected medicinal plants used in South-western Ethiopia

Traditional medicinal plants claim many traditional uses across different parts of the world. In Ethiopia, it remains the main source of treatment for the majority of human population and livestock. The aim of this study was to evaluate antibacterial activity of crude extracts of some traditional medicinal plants commonly used for traditional human medication in selected localities of Jimma Zone, Southwest Ethiopia. Data on ethno-botanical information and traditional uses of medicinal plants were gathered using semi-structured interview questionnaire involving a total of 30 experienced respondents of the study area. Candidate traditional medicinal plants were collected from Sigmo District of Jimma Zone, South western Ethiopia, labeled, processed, and extracted in accordance with standard procedures and the plant samples were deposited at Herbarium of Jimma University, Ethiopia. Antibacterial activities and minimum inhibitor concentration (MIC) of petroleum ether, chloroform and methanol extracts of leaves and stems of three frequently used plants [Kosteletzkya begonifolia, Leucas martinicensis, and Ranunculus multifidus] were evaluated against Staphylococcus aureus DSM 7346, Pseudomonas aeruginosa DSM 1117, Escherichia coli ATCC 25722 and Salmonella typhimurium ATCC 13311. Phytochemical constituents of the extracts were determined following standard analytical procedures. Results revealed that leaves were the most frequently used parts of the three medicinal plants. They are usually used for the treatment of tooth ache and gastro-intestinal ailments. The highest antimicrobial activities were observed in petroleum ether extract of K. begonifolia stems against S. aureus [Inhibition Zone (IZ), 28.3-30 mm], P. aeruginosa (IZ: 27-28.67 mm), E. coli (IZ: 28.3-31 mm) and S. typhimurium (IZ, 28-30.3)]. The extract displayed activity significantly closer to that of the control antibiotics, ciprofloxacin (IZ, 30-35 mm). Likewise, chloroform extracts of leaves of R. multifidus and methanol extracts of L. martinicensis displayed strong activities against S. aureus (IZ, 26.67±0.8 mm) and E. coli (IZ 26.67±3.3 mm), respectively. The lowest MIC observed in the current study was 5.6 mg/mL and recorded for both petroleum and chloroform extracts of leaves of R. multifidus, L. martinicensis, and K. begonifolia against S. aureus. The observed antibacterial activities could be accounted to combinations of phytochemical compounds isolated from the test plants including alkaloids, tannins, flavonoids, terpenoids and cardiac glycosides. Leaves of the three traditional medicinal plants evaluated in the current study displayed promising antibacterial activities against bacterial test strain. However, the highest activity was observed in petroleum ether extract of stems of K. begonifolia against all test strains with Inhibition Zone (IZ) diameter ranging between 28-31 mm. Further toxicity and pharmacokinetic study are recommended.