PHYTOCHEMICAL PROFILE, ANTIOXIDANT AND ANTIBACTERIAL ACTIVITIES OF POLYALTHIA LONGIFOLIA AND HYPTIS SUAVEOLENS LEAF EXTRACTS AGAINST SELECTED BACTERIAL PATHOGENS

Abstract

The increasing prevalence of antimicrobial resistance and the limitations associated with some conventional antimicrobial agents have intensified the search for bioactive compounds from medicinal plants. This study evaluated the phytochemical composition, antioxidant activity and antibacterial activity of aqueous and methanolic leaf extracts of Polyalthia longifolia and Hyptis suaveolens against selected bacterial pathogens. Dried leaf samples were extracted separately with distilled water and methanol by maceration. The extracts were screened qualitatively and quantitatively for selected phytochemicals. Antioxidant activity was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging and ferric-reducing antioxidant power (FRAP) assays. In contrast, antibacterial activity was determined by agar-well diffusion against Staphylococcus aureus, Escherichia coli, Haemophilus influenzae, Klebsiella pneumoniae and Streptococcus pyogenes. The extraction yields of methanolic and aqueous extracts of P. longifolia were 15.80% and 13.24%, respectively, while those of H. suaveolens were 18.89% and 49.63%, respectively. Tannins, phenols and terpenoids were detected in several extracts, while the distribution of other phytochemicals varied by plant species and extraction solvent. At 2 mg/mL, P. longifolia and H. suaveolens extracts exhibited DPPH radical-scavenging activities of 65.5% and 56.0%, respectively, compared with 40.1% for ascorbic acid. Their FRAP values were 399.50 and 373.00 μmol Fe(II)/g, respectively, compared with 300.25 μmol Fe(II)/g for ascorbic acid. Both plants demonstrated concentration-dependent antibacterial activity, with the greatest inhibition generally observed at 20 mg/mL. P. longifolia produced the largest inhibition zone (25.7 ± 1.52 mm) against E. coli, while H. suaveolens produced a maximum zone of 23.7 ± 0.58 mm against the same organism. However, the inhibition zones produced by the plant extracts were generally lower than those of ciprofloxacin. These findings show that P. longifolia and H. suaveolens leaves contain diverse phytochemicals and exhibit appreciable antioxidant and antibacterial activities, supporting their potential as sources of bioactive compounds for further investigation.