Bactericidal mechanisms and effector targets of TiO2 and Ag-TiO2 against Staphylococcus aureus

PURPOSE In our previous study, Ag+-loaded TiO2 and Ag+-loaded SiO2 coatings for tracheal intubation were prepared to prevent ventilator-associated pneumonia (VAP), but the antimicrobial targets and the underlying mechanisms of TiO2 and Ag-TiO2 (Ag+) are still unclear. We attempted to elucidate the antimicrobial activity and potential mechanisms against Staphylococcus aureus. METHODOLOGY The study tested the TiO2 and Ag+ bacteriostatic activity against S. aureus strains by MIC assays and S. aureus growth curves, lesion in the membranes by surface hydrophobicity tests, conductivity tests and measurements of DNA and RNA contents in S. aureus cultures, and investigated the inhibition of soluble protein and nucleic acid synthesis by measurements of soluble protein content, fluorescent intensity and nucleic acid content of living S. aureus. RESULTS The MIC values of TiO2 and Ag+ were 1.6 mg ml-1 and 5.781 µg ml-1. TiO2 and Ag+ could inhibit the growth of S. aureus. After treatment with TiO2 and Ag+, the surface hydrophobicity was significantly reduced, the conductivity of cultures increased, and DNA and RNA content in cultures showed no obvious changes. The expressions of soluble proteins and nucleic acid contents of living S. aureus were reduced after treatment with TiO2 and Ag+. CONCLUSION TiO2 and Ag+ could cause slight lesion in the membrane to affect S. aureus membrane permeability, but not decomposition of membrane. Moreover, TiO2 and Ag+ could lead to reduced expression of soluble protein by inhibiting the synthesis of nucleic acids, thereby further inhibiting the growth of S. aureus.