Antibacterial potential and in silico analysis of inflorescence-derived essential oils from three Eucalyptus species

Inflorescences represent a relatively underexplored source of essential oils (EOs); this investigation explores the chemical composition of three Eucalyptus species cultivated in Tunisia and their antibacterial efficacy. The GC-MS analysis showed that the EOs from Eucalyptus salubris and E. fasciculosa were dominated by oxygenated monoterpenes, chiefly eucalyptol. In contrast, E. stoatei displayed a more complex profile, rich in sesquiterpene hydrocarbons (mainly amorpha-4,7(11)-diene) and oxygenated sesquiterpenes, primarily spathulenol and maaliol. These compositional differences were reflected in the minimum inhibitory concentrations (MIC), which ranged from 14 to 18 µg/mL, depending on both the EOs tested and the bacterial strains. Antibiofilm activity, assessed by crystal violet and MTT assays, also varied according to the EOs and bacterial species. Molecular docking of the major constituents into the target proteins revealed that amorpha-4,7(11)-diene showed high binding affinities across all tested proteins, potentially linking its presence to the antibacterial effects observed for E. stoatei EOs. Moreover, all predicted compounds demonstrated promising pharmacokinetic profiles with no toxicity. Overall, Eucalyptus inflorescences emerge as valuable sources of EOs with distinctive bioactive compounds that contribute to their antibacterial efficacy.