Chemical Profile and In-Vitro Antibacterial, Biofilm-Inhibitory, Antioxidant, and Cytotoxic Activities of Cineole-rich Southern Blue Gum Essential Oil

Abstract

Eucalyptus globulus Labill essential oil was chemically characterized and evaluated for selected biological activities using integrated in vitro assays supported by exploratory in silico analysis. GC–MS profiling identified 8 constituents, with 1,8-cineole (eucalyptol) representing 90.51% of the total composition, indicating a cineole-dominant chemical profile. Antibacterial screening was performed against three clinical isolates and three reference strains, representing Gram-positive and Gram-negative bacteria. The essential oil produced inhibition zones ranging from 24.3 to 38.8 mm, with minimum inhibitory concentrations (MICs) of 62.5 to 125 µg/mL, depending on the strain. Biofilm biomass testing demonstrated concentration-dependent inhibition, with the strongest reduction observed for Pseudomonas aeruginosa (61.35% at 0.5 MIC). Antioxidant evaluation using DPPH and ABTS assays revealed dose-dependent radical scavenging activity. Cytotoxicity screening in Caco-2 and HepG2 cell lines showed concentration-dependent responses with IC₅₀ values of 24.4 ± 0.15 and 59.52 ± 0.35 µg/mL, respectively. Molecular docking suggested moderate interaction of eucalyptol with bacterial DNA gyrase through hydrophobic contacts and hydrogen bonding. This study provides integrated chemical and functional characterization of Eucalyptus globulus Labill oil and supports further investigation of eucalyptus-derived volatile compositions in antimicrobial and biofilm-control research, while indicating that additional pharmacological, selectivity, and in vivo studies are required before translational application.