Department of Chemical Engineering, Loughborough University, Loughborough, United Kingdom.
Clore Laboratory, University of Buckingham, Buckingham, United Kingdom.
J Photochem Photobiol B. 2019 Apr;193:131-139. doi: 10.1016/j.jphotobiol.2019.02.009. Epub 2019 Mar 1.
The aim of this study was to evaluate the bactericidal effect of reactive oxygen species (ROS) generated upon irradiation of photocatalytic TiO surface coatings using low levels of UVA and the consequent killing of Staphylococcus aureus. The role of intracellular enzymes catalase and superoxide dismutase in protecting the bacteria was investigated using mutant strains. Differences were observed in the intracellular oxidative stress response and viability of S. aureus upon exposure to UVA; these were found to be dependent on the level of irradiance and not the total UVA dose. The wild type bacteria were able to survive almost indefinitely in the absence of the coatings at low UVA irradiance (LI, 1 mW/cm), whereas in the presence of TiO coatings, no viable bacteria were measurable after 24 h of exposure. At LI, the lethality of the photocatalytic effect due to the TiO surface coatings was correlated with high intracellular oxidative stress levels. The wild type strain was found to be more resistant to UVA at HI compared with an identical dose at LI in the presence of the TiO coatings. The UVA-irradiated titania operates by a "stealth" mechanism at low UVA irradiance, generating low levels of extracellular lethal ROS against which the bacteria are defenceless because the low light level fails to induce the oxidative stress defence mechanism of the bacteria. These results are encouraging for the deployment of antibacterial titania surface coatings wherever it is desirable to reduce the environmental bacterial burden under typical indoor lighting conditions.
本研究旨在评估在低强度 UVA 照射下，光催化 TiO 表面涂层产生的活性氧（ROS）的杀菌效果，以及由此对金黄色葡萄球菌的杀灭作用。使用突变株研究了细胞内酶过氧化氢酶和超氧化物歧化酶在保护细菌方面的作用。研究发现，金黄色葡萄球菌在暴露于 UVA 时，其细胞内氧化应激反应和存活能力存在差异，这取决于辐照度水平而不是 UVA 总剂量。在低强度 UVA（LI，1 mW/cm）照射下，野生型细菌在没有涂层的情况下几乎可以无限期存活，而在存在 TiO 涂层的情况下，暴露 24 小时后就无法检测到存活的细菌。在 LI 下，TiO 表面涂层的光催化效应的致死性与细胞内氧化应激水平升高有关。与在 LI 下相同剂量的 TiO 涂层相比，野生型菌株在高强度 UVA 照射下更能抵抗 UVA。在低强度 UVA 照射下，TiO2 通过“隐形”机制起作用，产生低水平的细胞外致死性 ROS，细菌对此无能为力，因为低光水平不能诱导细菌的氧化应激防御机制。这些结果令人鼓舞，因为在需要在典型室内照明条件下降低环境细菌负荷的地方，可以部署抗菌 TiO2 表面涂层。
