Assessment of the Antibacterial Activity of Secondary Metabolites of Endophytic Bacteria Isolated from Senna occidentalis against some Clinical Multidrug-Resistant Bacteria

Endophytic bacteria are endosymbiotic bacteria that colonize the inter- or intracellular regions of plants, providing them with protection through cross-communication and the release of metabolites via their biosynthetic gene clusters. The emergence of new diseases due to rapid multidrug resistance against existing drugs has created an indisputable need for biologically active secondary metabolites. This study aimed to assess the antibacterial activity of secondary metabolites from endophytic bacteria isolated from Senna occidentalis against multidrug-resistant clinical bacterial isolates. Endophytic bacteria were isolated from the leaves, stems, and roots of S. occidentalis (coffee senna) and identified based on their cultural, microscopic, and biochemical characteristics. The Agar well diffusion method was employed to evaluate the endophytes for antibacterial activity against clinical isolates of Staphylococcus aureus, Salmonella Typhi, and Pseudomonas aeruginosa. A total of twenty-three endophytes were isolated from Senna occidentalis, and molecular identification using the 16S rRNA gene sequencing method was carried out for the three most active endophytic bacteria, each from the leaf, stem, and root of the plant, respectively. Screening using agar well diffusion method yielded mean inhibitory zones ranging from 30.00±0.00 (mm) to 12.00±0.00 (mm) for the secondary metabolites. Molecular identification revealed 99–100% sequence identity to related type strains in two major classes: Gammaproteobacteria (Escherichia sp.) and Bacilli (Bacillus sp.). The findings of this study suggest that endophytic bacteria from S. occidentalis can serve as a promising source of novel antimicrobial compounds with broad therapeutic significance.