In vitro antibacterial properties of selected medicinal plants used by traditional healers for gastrointestinal disorders in the Heban-Arsi and Kofale districts of Southern Ethiopia

In many previous studies, a number of medicinal plants used by traditional healers for gastrointestinal disorders have shown promising antibacterial activity in vitro. This study aimed to validate the antibacterial properties of nine indigenous Ethiopian medicinal plants traditionally used to treat gastrointestinal illnesses in Heban-Arsi and Kofale Districts of Southern Ethiopia. These include Syzygium guineense (Wild.) DC., Ximenia americana L., Bersama abyssinica Fresen., Vernonia amygdalina Delile, Olinia rochetiana A. Juss., Rumex nepalensis Sprengel, Euclea schimperi (A.DC.) Dandy, Prunus africana (Hook.f.) Kalkman, and Withania somnifera (L.) Dunal. The significance of this study lies in providing scientific evidence for the traditional use of these plants, thereby supporting the search for alternative treatments against bacterial pathogens. The in vitro assessment of antibacterial activity for 80% methanol leaf crude extracts from the nine plants were carried out at a concentration of 100 mg/ml against reference strains of Staphylococcus aureus ATCC 25,923, Escherichia coli ATCC 25,922, Pseudomonas aeruginosa ATCC 15,442, and Salmonella typhimurium ATCC 13,311, and their clinical isolates, employing the agar-well diffusion method to validate the claims made by traditional healers. Furthermore, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) value of the two most effective crude extracts and their different solvent fractions were determined using the micro-broth dilution method. Initial phytochemical screenings of the crude extracts were also conducted using chemical and chromatographic methods. The crude extracts of the leaves from nine medicinal plants and fractions of the most promising extracts, demonstrated antibacterial properties against all tested bacteria, though the degree of inhibition varied among the plants and target organisms. Notably, the crude extracts and certain fractions from S. guineense (Willd.) DC., and O. rochetiana A. Juss., exhibited strong antibacterial activity, with mean growth inhibition zones ranging from 10 ± 0.66 mm to 26 ± 0.11 mm for S. guineense and 9 ± 0.10 mm to 25 ± 0.77 mm for O. rochetiana. The 80% methanol extract of S. guineense had a minimum inhibitory concentration (MIC) of 1.56 mg/ml and a minimum bactericidal concentration (MBC) value of 6.25 mg/ml against standard S. aureus. The chloroform fraction of O. rochetiana exhibited an MIC and value MBC of 3.125 mg/ml and 12.5 mg/ml, respectively, against standard S. aureus. Preliminary phytochemical screenings of the crude extracts revealed the presence of major phytochemical groups including alkaloids, flavonoids, saponins, terpenoids and tannins. The number of spots detected in TLC profiling of crude extracts further supported the antibacterial activity observed in the crude extracts. This study has validated the traditional uses of medicinal plants by local healers for treating gastrointestinal diseases like diarrhea. Future research should focuses on safety levels, isolation and structural elucidation of the active compounds responsible for the observed antibacterial activities particularly from the most promising crude extracts and active fractions of S. guineense and O. rochetiana. Overall, investigating the antibacterial properties of medicinal plants could enhance medical science, expand treatment options and ethnopharmacological based drug discovery, and contribute to global health solutions.