Antibacterial Activity and Mechanism of Thyme Essential Oil Nanoemulsion Prepared with Potato Protein Modified by Transglutaminase(TGase) against Staphylococcus aureus and Escherichia coli: A Metabolomic Study

In this study, thyme essential oil (TEO) nanoemulsion (tPTNs) was constructed with transglutaminase (TGase)-modified potato protein, and its antibacterial activity and mechanism of action were evaluated and explored. Results indicated that tPTNs exhibited great antibacterial activity against both Staphylococcus aureus and Escherichia coli, with minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 2.5 and 5.0 mg/m L, respectively. Also, the antibacterial effects of tPTNs were concentration-dependent. We observed a significant decrease in the absolute value of the zeta potential, and significant increases in particle size, cell membrane hydrophobicity, conductivity, the release of metal ions, and the leakage of nucleic acid as the concentration of tPTNs increased from 0 mg/m L to MBC. Furthermore, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that protein synthesis was inhibited or even disrupted. Analysis by liquid chromatography-mass spectrometry (LC-MS) indicated that treatment with tPTNs caused significant changes in bacterial metabolites, 1117 and 692 differential metabolites being found for S. aureus and E. coli, respectively. The differential metabolites were involved in nucleotide metabolism, amino acid metabolism, tricarboxylic acid cycle and other metabolic pathways. These findings provide valuable insights for the application of thyme essential oil as an efficient antibacterial agent and for the understanding of its mechanism of action.