Oil-in-water nanoemulsification of peppermint oil enhances its antibacterial and antibiofilm activity.

Peppermint essential oil (PEO) exhibits broad antimicrobial activity but suffers from poor aqueous dispersibility, volatility, and limited physicochemical stability. To overcome these limitations, an oil-in-water peppermint essential oil nanoemulsion (PEONE) was formulated using Brij®58 and Span®80 surfactants via careful optimization of ultrasonication technology that resulted development of spherical droplets of ∼40 ± 9 nm. The formulation was found to be stable for ∼28 days and exhibited negligible coalescence and Ostwald ripening and a low creaming index (∼1.42-2%) over 60 days. PEONE exhibited significantly enhanced antibacterial activity compared to native PEO, with MIC50 values of ∼18.22 μL/mL against Staphylococcus aureus and ∼35.55 μL/mL against Escherichia coli, corresponding to ∼2.4 and ∼3.3-fold higher efficacy, respectively. PEONE also showed potent antibiofilm activity, eradicating mature biofilms (MBEC50 ∼333 μL/mL for S. aureus and ∼300.7 μL/mL for E. coli). In practical assays, PEONE spray reduced surface bacterial loads by ∼83% (for S. aureus) and ∼48% (for E. coli), outperforming a commercial sanitizer, and decreased bacterial adhesion via enhanced surface hydrophilicity (contact angle reduced from ∼80° to ∼50°). These results support PEONE as a robust plant-based antimicrobial formulation for hygiene and biomedical surface/device applications.