Antibacterial activity and phytochemical screening of Rumex abyssinicus Jacq and Verbascum sinaiticum Benth collected from Debre Markos, northwest Ethiopia

Abstract Background The increasing challenge of antibiotic resistance necessitates the need to explore alternative antimicrobial agents derived from natural sources. Rumex abyssinicus Jacq and Verbascum sinaiticum Benth are well-regarded in Ethiopian traditional medicine for their therapeutic potential. This study thus aimed to assess the antibacterial activity and phytochemical screening of extracts from the roots of R. abyssinicus and the leaves of V. sinaiticum collected from Debre Markos, northwest Ethiopia. Methods Crude extracts were prepared using a 1:10 w/v cold maceration technique with 80% ethanol and chloroform as solvents. In vivo, toxicity was assessed using Galleria mellonella larvae exposed to extracts at concentrations ranging from 12.5 to 100 mg/ml. Antibacterial activities were evaluated using disc diffusion assays against four strains of human pathogenic bacteria at concentrations ranging from 25 to 200 mg/ml. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were also determined to quantify the potency of the extracts. Phytochemical analysis identified secondary metabolites using standard qualitative tests, while chromatographic techniques: thin layer chromatography (TLC), and high-performance liquid chromatography (HPLC) were conducted for fractionation, followed by nuclear magnetic resonance spectroscopic (NMR) characterization, and mass spectrometry (MS) of isolated compounds. Results Toxicity assessments of the plant extracts on G. mellonella larvae indicated dose-dependent toxic effects, with 100 mg/ml causing 40% mortality, suggesting moderate toxicity. Yet, mortality decreased at lower concentrations. Both plant extracts demonstrated significant (p < 0.05) antibacterial activity against all tested bacteria. The ethanol extract of R. abyssinicus exhibited the highest activity against Staphylococcus aureus (inhibition zone: 21.3 ± 1.21 mm) at 200 mg/ml. However, chloroform extracts of V. sinaiticum did not exhibit response at concentrations of 50 mg/ml and 25 mg/ml. MIC values for ethanol extracts of R. abyssinicus were consistent at 32 mg/ml across the majority of tested bacteria, while chloroform extracts of V. sinaiticum showed higher MIC values (64 mg/ml), indicating lower potency. Phytochemical analysis revealed the presence of anthraquinones, saponins, and tannins in R. abyssinicus, and flavonoids and phenols in V. sinaiticum. In addition, chromatographic separation yielded compounds such as chrysophanol and emodin from R. abyssinicus, and luteolin and aucubin from V. sinaiticum extracts. Conclusion Ethanol extracts from R. abyssinicus roots and V. sinaiticum leaves exhibit potent antibacterial activity against tested pathogens, supported by their diverse phytochemical profiles. These findings underscore their potential as sources of antibacterial agents, warranting further investigation into their therapeutic applications.