Antibacterial activity of selected plants used in traditional medicine from Gedeo zone, Ethiopia against multidrug-resistant wound bacterial isolates.

Developing new drugs and identifying alternative sources of antimicrobial leads in the context of emerging multidrug resistance (MDR) are extremely important. In Ethiopia, medicinal plants are often used by traditional healers owing to their affordability, ease of access, and efficacy. Many plants have well-documented antimicrobial activity and contain bioactive compounds, which are even effective against multidrug-resistant bacteria. This study aims to determine the in vitro antimicrobial activity of three selected traditional medicinal plants against MDR wound bacterial isolates. An in vitro experimental study was conducted on three traditionally used medicinal plants: Ajuga integrifolia (roots and stems), Ocimum lamiifolium (leaves), and Ruta chalepensis (aerial parts). These plant parts were collected from various fields and the Dilla University Botanical Garden and were authenticated by a botanist. Following cleaning and shade drying, they were ground into powder and extracted by means of maceration with diethyl ether and absolute methanol (MeOH) (1:10 w/v) independently. The antimicrobial activities of the extracts obtained were tested against four MDR wound isolates, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes using both the Kirby-Bauer disc diffusion method and the minimum inhibitory concentration (MIC) method and time kill kinetic assay, following the guidelines of the Clinical Laboratory Standards Institute (CLSI). All the six crude extracts showed varying degrees of antimicrobial activity against all four tested MDR wound isolates. Remarkably, the MeOH extracts of the parts of all the three selected plants exhibited higher zones of inhibition against bacteria compared to the ethereal extracts. The leaf extracts of O. lamiifolium demonstrated superior efficacy compared to others; the highest inhibition zones, 21.04 ± 0.57 and 19.7 ± 0.43 mm, were shown against drug-resistant burn wound strains of P. aeruginosa and methicillin-resistant S. aureus, respectively. In contrast, the ethereal extract of the aerial parts of R. chalepensis was ineffective, with an inhibition zone of only 8.5 ± 0.78 mm. The obtained MIC values of O. lamiifolium correspond to the range of 0.5 × 103 to 1 × 103 µg/mL, and minimum bactericidal concentration (MBC) values observed were within the range of 1 × 103 to 2 × 103 µg/mL. The time-kill kinetics showed a dose-dependent bactericidal activity against P. aeruginosa, achieving a ≥ 3 log₁₀ colony forming units/mL (CFU/mL) reduction within 2 h at concentrations of 4× and 8× MIC. This research examines the antibacterial effects of extracts from various parts of three selected plants, substantiating their traditional use in treating wound infections and providing a baseline for future investigation. It also highlights the probable ethnobotanical uses of O. lamiifolium; in particular, which may be a promising candidate in the search for new antimicrobial drugs.