Total Phenolic and Flavonoid Contents, Antibacterial Evaluation, and Bioactive Compounds Identification in Calliandra surinamensis Benth. cultivated in Egypt

Calliandra surinamensis is an ornamental plant widely distributed across tropical and subtropical regions, and it is cultivated in Egypt. Despite its traditional use, there have been limited studies exploring its phytochemical composition and biological activities. This study aimed to evaluate the total phenolic and flavonoid contents of the plant crude methanolic extract along with phenolic-rich fractions, to isolate phytoconstituents from the most active fraction using different chromatographic techniques, to identify their structures using 1H and 13C NMR techniques, and to assess the antibacterial activity of the extract and all subsequent fractions. The ethyl acetate fraction exhibited the highest total phenolic and flavonoid content. Phytochemical investigation of this fraction led to the isolation of four phenolic compounds: methyl gallate, kaempferol-3-O-rhamnoside (afzelin), quercetin-3-O-rhamnoside (quercitrin), and myricetin-3-O-rhamnoside (myricitrin). Interestingly, the ethyl acetate fraction showed the strongest antibacterial activity against Escherichia coli bacterial strains. These findings suggest that C. surinamensis may serve as a promising source of natural antioxidants and antibacterial agents. Further in vivo studies are recommended to confirm its safety and therapeutic potential.