Rhus coriaria L. (sumac) leaves harbour robust antimicrobial activity

Introduction: Rhus coriaria L. (sumac) has various medicinal properties, with the antibacterial activity of its fruit particularly well known. Building on earlier research, this project focused instead on the less-studied antimicrobial effect of Rhus coriaria L. leaves. Methods: Leaf extracts were fractionated and sub-fractionated using high-performance liquid chromatography (HPLC). The most active subfraction (Rs5) was analyzed by liquid chromatography-mass spectrometry (LCMS). The antibacterial activity of the extracts was assessed according to well- and disk-diffusion methods. Results: Crude leaf extracts, their fractions, and subfractions all showed substantial antibacterial activity, with minimum inhibitory concentration (MIC) values ranging from 0.2–3.1 mg/mL, depending on the fraction and the bacteria species. Subfraction Rs5 had the strongest antibacterial activity with a MIC of 0.4 mg/mL. Rs5 incorporated into a commercial eye drop formula also exhibited antibacterial activity. Notably, the crude leaf extract also showed antifungal activity against the agricultural pest B. cinerea. LCMS analysis revealed that Rs5 subfraction contains mainly flavonoids, tannins, and antioxidants, which may be the active compounds. Conclusions: Rhus coriaria L. crude leaf extracts and their fractions exhibit antimicrobial activity. The leaves, available in greater quantities and regularly throughout the year in comparison to the plant's fruit, are therefore a cheaper and more effective resource for developing sumac-based antimicrobial products to be used in the food and agricultural industries.