Phytochemical Profiling, Antimicrobial Activity and Characterization of Bioactive Compound from Eucalyptus Globulus Leaf Extracts

Abstract

Eucalyptus globulus is a medicinal plant widely employed in traditional healthcare systems for managing respiratory infections, wounds, and inflammatory disorders. Despite its ethnomedicinal relevance, the antimicrobial potential of its chemically characterized leaf fractions remains underexplored. This study was designed to screen the phytochemical constituents, isolate bioactive fractions, evaluate antimicrobial activity, and structurally characterize the most potent fractions from methanolic leaf extracts of E. globulus. Fresh leaves were collected, air-dried, powdered, and extracted with methanol. Qualitative phytochemical screening was conducted using standard protocols. Bioactive compounds were separated via thin-layer chromatography (TLC) and column chromatography. Antimicrobial activity was assessed against four pathogenic bacteria (Staphylococcus sp., Escherichia coli, Salmonella typhi, and Pseudomonas sp.) using the agar well diffusion method at concentrations ranging from 1.25 to 15.00 mg/mL. The most active fractions (F1 and F2) were characterized using FT-IR spectroscopy and gas chromatography-mass spectrometry (GC-MS). Phytochemical screening revealed the presence of terpenoids, alkaloids, flavonoids, tannins, saponins, glycosides, volatile oils, and phenols. Column chromatography yielded six fractions with distinct polarity profiles. Antimicrobial testing established a clear polarity-activity relationship, with fraction F1 demonstrating the highest overall potency, particularly against E. coli (zone of inhibition: 30.27 mm; MIC: 2.50 mg/mL). Fraction F2 exhibited selective activity against S. typhi (28.63 mm; MIC: 2.50 mg/mL). FT-IR analysis confirmed C-H, C=O, C-C, C-Cl and C–O functional groups. GC-MS identified sesquiterpenes (aromadendrene, β-guaiene, alloaromadendrene) and long-chain aliphatic hydrocarbons in F2, while F1 was dominated by very-long-chain alkenes, including Z-14-nonacosane (16.90%) and 1-hexacosene (10.61%). The methanolic extract of E. globulus is rich in diverse bioactive phytochemicals. Non-polar fractions, particularly F1 and F2, exhibit significant antimicrobial activity attributable to sesquiterpenes and long-chain hydrocarbons. These findings validate the traditional medicinal use of E. globulus and highlight its potential as a source of natural antimicrobial agents for pharmaceutical development.