Isolation and Characterisation of Antimicrobial Compounds from Stem Bark of Erythrina senegalensis Collected in Niger State, North Central Nigeria

The escalating global crisis of antimicrobial resistance demands a renewed commitment to natural product-based drug discovery, with African plant biodiversity offering significant untapped chemical diversity. Erythrina senegalensis, distributed across the Guinea savannah zones of North Central Nigeria including Niger State, is used by the Nupe and Gbagyi peoples for infections of the skin, respiratory tract, and urogenital system. This study isolates and characterises antimicrobial compounds from the stem bark of Erythrina senegalensis through bioassay-guided fractionation. Crude methanol bark extract was sequentially partitioned, and fractions were screened against methicillin-resistant Staphylococcus aureus (MRSA), Klebsiella pneumoniae, Pseudomonas aeruginosa, and Candida albicans using broth microdilution. The most active fraction was subjected to silica gel column chromatography and preparative TLC. Isolated compounds were characterised by 1H and 13C NMR, COSY, HMBC, HSQC, and HR-ESIMS analyses. Four alkaloids of the erythrinane class and two flavanone glycosides were characterised, including one previously undescribed erythrinane analogue. The novel compound demonstrated MIC values of 1.95 ug/mL against MRSA and 3.9 ug/mL against C. albicans. Synergistic activity with amoxicillin-clavulanate was demonstrated against MRSA in checkerboard assays. These results establish Erythrina senegalensis as a promising source of novel antibiotics and support further mechanism-of-action and toxicological studies. Keywords: Erythrina senegalensis, antimicrobial, MRSA, erythrinane alkaloids, Niger State