Tea Tree Oil Nanoemulsion Potentiates Antibiotics against Multidrug-Resistant Escherichia coli.

Extensive efforts are underway to overcome the rising prevalence of antibiotic resistance. Combination therapy may be a potential method to treat multidrug-resistant (MDR) bacterial infections. In this study, tea tree essential oil (TTO) nanoemulsion (nanoTTO) was used in combination with antibiotics to kill microbes. Results showed that nanoTTO enhanced the activities of multiple antibiotics against MDR Escherichia coli (E. coli), and its antimicrobial activity was not changed against bacteria that were cultured in the presence of nanoTTO for 30 passages. Further studies to visualize and quantify intracellular antibiotics concentrations identified that nanoTTO increased the drug accumulation in MDR E. coli by disrupting outer and inner membranes and inhibiting the AcrAB-TolC efflux pump involved in membrane permeability. In addition, nanoTTO was effective in enhancing antibiotic efficacy in the Galleria mellonella infection model and mouse peritonitis model, suggesting a potential strategy against MDR bacterial infections.