Ultrasonic preparation of Tween-essential oil (Zanthoxylum schinifolium Sieb. et Zucc) oil/water nanoemulsion: Improved stability and alleviation of Staphylococcus epidermidis biofilm

Abstract

Staphylococcus epidermidis has been identified as a pathogen in ready-to-eat foods, and its biofilm can cause devastating chronic infections in affected hosts. For the demand of natural antibacterial reagents and overcoming their inherent properties, nanoemulsions are increasingly being used in the delivery of natural drugs. The nanoemulsion obtained by ultrasonic technology has the advantages of small droplet size , low polydispersity index (PDI), high stability and small amount of surfactant. Therefore, ultrasonic technology was used to prepare Zanthoxylum schinifolium Sieb. et Zucc essential oil nanoemulsion (ZEO-NE), a novel antibiofilm nanoemulsion with a mean particle size of 105.6 nm, polydispersity index of 0.278, and Zeta potential of − 22.3 mV. Assessment of antibacterial activity defined the minimum inhibitory concentration (MIC) and minimum bactericidal concentration of ZEO-NE against S. epidermidis as 2.5 and 5.0 mg/mL, respectively. Meanwhile, the antibiofilm assays revealed that the inhibition rate of ZEO-NE at sub-MIC levels (1/16–1/2 MIC) against S. epidermidis biofilm formation was 4.65–81.38 %. Further studies showed that sub-MIC ZEO-NE can effectively inhibit the formation of biofilms by extracellular polymeric substances and regulate gene expression of biofilm initial adhesion, formation, and quorum-sensing systems. Meanwhile, the inhibition rates of ZEO-NE (1/2–4 MIC) on preformed biofilm biomass and cell metabolic activity were 45.06–72.40 % and 30.72–62.54 %, respectively. In addition, electron microscopy analysis showed that ZEO-NE can destroy the established biofilms to a great extent. Finally, cytotoxicity evaluation experiments showed that ZEO-NE could damage human immortalized keratinocytes . These findings indicate that nanotechnology is an effective strategy to increase ZEO stability and solubility, and the prepared ZEO-NE is a viable candidate to inhibit S. epidermidis and its biofilms. • A high-quality ZEO-NE with a size of 105.6 nm, PDI of 0.278 and Zeta potential of − 22.3 mV was obtained. • The ZEO-NE can strongly inhibit Staphylococcus epidermidis and its biofilms. • The ZEO-NE can down-regulate the expression of virulence genes of S. epidermidis . • The ZEO-NE can effectively destroy the stable structure of the preformed biofilm.