Abstract
PurposeIn 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.MethodologyThe 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.ResultsThe 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+.ConclusionTiO2 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.
Highlights
TiO2 is one of the most important semiconducting oxides because of its photocatalytic activity, conservative properties, low cost, low toxicity and stability in response to light illumination [1] TiO2 has a high band gap energy (3.2 eV), which limits its wide applications in the visible light range of the solar spectrum [2, 3]
The expressions of soluble proteins and nucleic acid contents of living S. aureus were reduced after treatment with TiO2 and Ag+
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
Summary
TiO2 is one of the most important semiconducting oxides because of its photocatalytic activity, conservative properties, low cost, low toxicity and stability in response to light illumination [1] TiO2 has a high band gap energy (3.2 eV), which limits its wide applications in the visible light range of the solar spectrum [2, 3]. To enhance the generation of reactive oxygen species by TiO2 nanomaterials under conditions of visible light irradiation, noble metals such as Pd, Pt, Au and Ag have been used to modify TiO2 [5,6,7,8,9,10,11]. Among these noble metals, Ag has attracted significant attention for doping TiO2 to inactivate bacteria because of its excellent broad-spectrum antibacterial properties, heat resistance, good dispersion and low drug resistance [12]. Heidenau et al found that an Ag+ concentration of 3.5 μM was not cytotoxic to mouse L929
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