Microscopical characteristics, phytochemical screening and antimicrobial activity of different fractions of Litsea monopetala leaves

Background: Litsea monopetala (Lauraceae) is a medicinal plant widely distributed in tropical and subtropical regions. Previous studies have reported its antimicrobial, antioxidant, and anti-inflammatory properties. However, data on the microscopical characteristics and chemical constituents of L. monopetala in Vietnam remain scarce. This study aimed to provide detailed anatomical and powder descriptions of the leaves, to perform preliminary phytochemical screening, and to evaluate the antibacterial potential of different solvent fractions against Staphylococcus aureus, including methicillin-resistant strains (MRSA). Methods: Leaves of L. monopetala were collected from Pu Huong National Park, Vietnam. Anatomical and powder features were examined using standard double-staining methods under a light microscope. Preliminary phytochemical tests were conducted with common reagents to detect major secondary metabolite groups. Crude ethanol extracts were fractionated with n-hexane, ethyl acetate, and water. Thin-layer chromatography (TLC) was performed to compare phenolic and flavonoid profiles among the fractions. Antibacterial activity was evaluated in vitro against methicillin-susceptible S. aureus (MSSA, ATCC 25923) and MRSA (ATCC 33591) by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using broth microdilution according to CLSI guidelines. Results: Microscopical analysis revealed distinct diagnostic features of L. monopetala leaves, including uniseriate epidermis with unicellular covering trichomes, palisade mesophyll, and calcium oxalate crystals. Powder microscopy showed fragments of epidermis, stomata, fibers, vessel elements, and oxalate crystals. Phytochemical screening detected six groups of compounds: flavonoids, tannins, sterols, reducing sugars, amino acids, and lipids. TLC confirmed that the ethyl acetate fraction was rich in phenolics and flavonoids, displaying strong fluorescent spots under UV light after NP/PEG derivatization. Antibacterial assays demonstrated that ethyl acetate fraction exhibited the strongest inhibitory activity with MIC values of 1 mg/mL against both MSSA and MRSA, although no clear bactericidal effect (MBC) was observed at tested concentrations. The n-hexane and water fractions showed weaker activity, inhibiting MRSA only at MIC = 4 mg/mL. Conclusions: This study provides the first comprehensive microscopical description and phytochemical screening of L. monopetala leaves from Vietnam, along with evidence of significant antibacterial activity, particularly in the ethyl acetate fraction. The results suggest that flavonoids and related phenolic compounds concentrated in this fraction may serve as promising candidates for developing novel anti-staphylococcal agents, especially against drug-resistant strains such as MRSA.