Phytochemical screening and antibacterial activity of the methanolic extract of 'Indigofera oblongifolia' leaves naturally grown in Saudi Arabia

The growing prevalence of drug-resistant pathogens necessitates the search for novel antimicrobial agents. This study evaluated the antimicrobial and antibiofilm activities of the methanolic leaf extract of Indigofera oblongifolia against selected Gram-positive (Listeria monocytogenes ATCC 7644 and Staphylococcus aureus ATCC 25923) and Gram-negative bacteria (Escherichia coli ATCC 8739 and Salmonella enterica ATCC 14028). The methanolic extract was prepared, and its phytochemical composition was analyzed. Qualitative analysis revealed the presence of phenolics, flavonoids, tannins, and saponins, with phenolics being the predominant constituents. Antimicrobial activity was assessed using the agar well-diffusion method, while antibiofilm activity was determined by the microtiter plate assay. The extract exhibited pronounced antibacterial effects against Gram-positive strains, whereas Gram-negative bacteria showed limited susceptibility. Furthermore, the extract significantly inhibited biofilm formation in L. monocytogenes and E. coli, while a slight enhancement of biofilm production was observed in S. enterica. These results indicate that I. oblongifolia leaves possess bioactive compounds with potent antimicrobial and antibiofilm properties. Further studies are recommended to isolate and characterize the active constituents and elucidate their mechanisms of action, which may support the potential development of plant-derived alternative therapeutic agents.