Nanoemulsification Promotes Antibacterial Activity of Selected Essential Oils Against Multidrug-Resistant...

Essential oils (EOs) are unique materials with healing powers that have been extensively reported. Yet their full antimicrobial potential is still underexplored due to their complex molecular properties, high viscosity, and low solubility, which limit their wide pharmaceutical application. In this study, we report the formulation of water-soluble nanoemulsions (NEs) of three EOs, namely, Artemisia vulgaris, Rhododendron anthopogon, and Eremophila mitchellii. The prepared NEs had an average particle diameter between 190 and 230 nm and remained physically stable at 4°C for up to 6 months. Most importantly, the fabricated NEs enhanced the antibacterial activity of the EOs against a multidrug-resistant Staphylococcus aureus clinical isolate by eightfold, with the EO having a median minimum inhibitory concentration (MIC) of 64 mg/mL, whilst the NEs had a median value of 8 mg/mL. Moreover, the NEs reduced the biofilm viability by up to > 6 log₁₀ compared with the control groups. Among the tested EOs, E. mitchelli showed the strongest antibacterial activity, with MIC values of 16 and < 0.125 mg/mL for the EO and NE, respectively. In addition, E. mitchellii NE nearly eradicated S. aureus biofilms at 10 mg/mL across all strains. Safety studies against human foreskin fibroblasts indicated a harmless effect of the excipients used in the fabrication process, where the viability of cells exposed to the NEs of E. mitchellii and A. vulgaris was > 70% and 90%, respectively. These findings highlight the successful fabrication of EO-based NEs with potent antibacterial activity against multidrug-resistant S. aureus clinical isolates in vitro.