Phytochemical Synergy and Antibacterial Activity of Crude and Fractionated Extracts of Senna occidentalis and Croton zambesicus Targeting Multidrug-Resistant Pathogens

Introduction: The escalating burden of multidrug-resistant (MDR) bacterial infections has intensified the search for alternative antimicrobial agents. Medicinal plants rich in bioactive metabolites provide a promising source of new therapeutic leads. This study evaluated the in vitro antimicrobial activity of crude and fractionated leaf extracts of Senna occidentalis and Croton zambesicus against selected MDR clinical bacterial isolates. Methods: Crude extracts were obtained by maceration and fractionated using liquid–liquid partitioning. Antibacterial activity was assessed via agar well diffusion and broth dilution assays. Minimum inhibitory (MIC) and bactericidal concentrations (MBC) were determined, and phytochemical composition was characterized using Gas Chromatography–Mass Spectrometry (GC–MS). Results: Crude extracts exhibited broad-spectrum activity, with inhibition zones ranging from 12.67 ± 0.67 mm to 18.00 ± 0.00 mm. Fractionation reduced overall potency, though select n-hexane and ethyl acetate fractions retained moderate activity. MIC and MBC values indicated a concentration-dependent transition from bacteriostatic to bactericidal effects. GC–MS analysis revealed major constituents including unsaturated fatty acids, long-chain aldehydes, phytol derivatives, and sesquiterpenes. Conclusion: S. occidentalis and C. zambesicus demonstrate notable antimicrobial potential, supporting further exploration for plant-based antibacterial agents and targeted isolation of bioactive compounds.