Antimicrobial Activity and Bioactive Constituents of Methanol Extracts of Cassia Senna (Senna alexandrina Mill)

Abstract

Medicinal plants remain important sources of antimicrobial compounds, particularly as antibiotic resistance increases. This study evaluated the antimicrobial activity and bioactive constituents of methanol extracts from the flowers, leaves and stems of Senna alexandrina Mill. (Cassia senna) against selected bacterial and fungal pathogens. Extracts were tested against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Candida albicans and Aspergillus spp. at concentrations of 50–200 mg/ml using agar well diffusion, followed by MIC, MBC/MFC and GC-MS analyses. Antimicrobial activity was concentration dependent and varied among plant parts. The flower extract showed minimal activity, with weak inhibition of S. aureus only at 200 mg/ml. Leaf and stem extracts showed broader activity; the leaf extract inhibited all tested organisms at 200 mg/ml, with inhibition zones ranging from 8.0 to 13.3 mm, whereas the stem extract produced the highest inhibition against S. aureus (16.0 mm) and C. albicans (15.0 mm). MIC/MBC values indicated greater sensitivity of Gram-positive bacteria than Gram-negative bacteria and fungi. GC-MS profiling identified 20 compounds in the leaf extract, dominated by sparteine (24.93%), and 60 compounds in the stem extract, with docosane, 2,21-dimethyl- (8.29%) as the major constituent. The findings support further investigation of leaf and stem extracts as sources of antimicrobial constituents.