Antibacterial Activity and Phytochemical Composition of Ethanolic and Aqueous Leaf Extracts of Vernonia galamensis Against Selected Pathogenic Bacteria

Abstract

The rising prevalence of antimicrobial resistance has intensified the search for alternative therapeutic agents from medicinal plants. This study evaluated the antibacterial activity and qualitative phytochemical composition of ethanolic and aqueous leaf extracts of Vernonia galamensis against selected pathogenic bacteria. Fresh leaves of V. galamensis were collected, authenticated, air-dried, and extracted using ethanol and distilled water. Qualitative phytochemical screening was performed to detect alkaloids, tannins, flavonoids, saponins, phenols, phytate, and oxalate using standard chemical tests. Antibacterial activity of the extracts at concentrations of 25 mg/mL, 50 mg/mL, and 100 mg/mL was assessed against Salmonella typhi and Staphylococcus aureus using the disc diffusion method. Ciprofloxacin (250 mg) and dimethyl sulfoxide served as positive and negative controls, respectively. Phytochemical analysis revealed solvent-dependent variation in constituent distribution. Alkaloids were strongly present in the ethanolic extract but absent in the aqueous extract, while tannins, flavonoids, saponins, and phenols were more pronounced in the aqueous extract. Both extracts contained moderate levels of phytate, whereas oxalate was more abundant in the ethanolic extract. The antibacterial assay demonstrated concentration-dependent inhibition against both test organisms. The ethanolic extract showed higher antibacterial activity, producing inhibition zones of up to 15 mm against S. typhi and 14 mm against S. aureus at 100 mg/mL. Although ciprofloxacin exhibited greater activity, the findings highlight the antibacterial potential of V. galamensis and support its ethnomedicinal use as a source of bioactive compounds for complementary antimicrobial development.