Mechanisms of Triton X-100 reducing the Ag⁺-resistance of Enterococcus faecalis

To investigate the mechanism of Triton X-100 (TX-100) reducing the Ag⁺-resistance of Enterococcus faecalis (E. faecalis), and evaluate the antibacterial effect of TX-100 + Ag⁺ against the induced Ag⁺-resistant E. faecalis (AREf). The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of AgNO₃ against E. faecalis with/without TX-100 were determined to verify the enhanced antibacterial activity. Transmission electron microscopy (TEM) was used to observe the morphological changes of E. faecalis after treatment. The intra- and extracellular concentration of Ag⁺ in treated E. faecalis was evaluated using inductively coupled plasma mass spectrometer (ICP-MS). The changes in cell membrane potential and integrity of treated E. faecalis were also observed using the flow cytometer. Moreover, AREf was induced through continuous exposure to sub-MIC of Ag⁺ and the antibacterial effect of TX-100 + Ag⁺ on AREf was further evaluated. The addition of 0.04% TX-100 showed maximal enhanced antibacterial effect of Ag⁺ against E. faecalis. The TEM and ICP-MS results demonstrated that TX-100 could facilitate Ag⁺ to enter E. faecalis through changing the membrane structure and integrity. Flow cytometry further showed the effect of TX-100 on membrane potential and permeability of E. faecalis. In addition, the enhanced antibacterial effect of TX-100 + Ag⁺ was also confirmed on induced AREf. TX-100 can facilitate Ag⁺ to enter E. faecalis through disrupting the membrane structure and changing the membrane potential and permeability, thus reducing the Ag⁺-resistance of E. faecalis and enhancing the antibacterial effect against either normal E. faecalis or induced AREf.