Antibacterial and antioxidant potential of Eucalyptus globulus against biofilm-forming bacteria

Eucalyptus globulus, a versatile evergreen native to Africa and Asia, has been globally recognized for its medicinal properties, mainly because of its rich phytochemical content, including eucalyptol, flavonoids, and terpenoids. This study examined the antibacterial and antioxidant potential of E. globulus leaf extracts against biofilm-forming pathogens (Staphylococcus aureus, Escherichia coli, and Salmonella typhi), which are becoming increasingly resistant to standard antibiotics. Leaves were collected, authenticated (voucher ASP-1725), and extracted using reflux extraction with N-hexane and water-based solvents. Phytochemical screening identified alkaloids, flavonoids, phenols, tannins, and terpenoids in the N-hexane extract; meanwhile, the aqueous extract contained phenols, tannins, steroids, and saponins. Antibacterial activity was tested through agar well diffusion and broth dilution methods. Both extracts showed concentration-dependent inhibition, with the aqueous extract being more effective against S. aureus (15.03 ± 0.38 mm at 100 mg/mL) and S. typhi (MIC: 12.5 mg/mL). The N-hexane extract was more effective against E. coli (14.07 ± 0.22 mm at 100 mg/mL), although amoxicillin controls displayed significantly higher activity. Minimum bactericidal concentration (MBC) values ranged from 12.5 to 50 mg/mL, with S. aureus being the most susceptible. Antioxidant tests revealed significant activity, with the aqueous extract exhibiting the highest ascorbic acid equivalent (AAE) capacity (78.63 ± 0.19 μg/mL), which is attributed to its high phenolic and flavonoid levels. These results support traditional uses of E. globulus and suggest its potential as a supplementary antimicrobial agent in the face of rising antibiotic resistance. The study emphasizes the importance of solvent choice in phytochemical extraction, with water-based extracts showing greater effectiveness against Gram-negative bacteria. Further research is needed to isolate active compounds and explore possible synergistic effects with standard antibiotics.