TiOb>2b> nanoparticles suppress Escherichia coli cell division in the absence of UV irradiation in acidic conditions

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• 作者：Lyudmila V. Zhukova^a ; John Kiwi^b ; ^{john.kiwi@epfl.ch} ; Vitaly V. Nikandrov^a
• 关键词：TiO2 ; Nanoparticles ; Escherichia coli ; Antimicrobial effect ; TiO2 dark reactions
• 刊名：Colloids and Surfaces B ; Biointerfaces
• 出版年：2012
• 期刊代码：14_09277765
• 类别：ms
• 出版时间：1 September, 2012
• 卷：97
• 期：Complete
• 页码：240-247
• 文件大小：1176 K

摘要

TiOb>2b> nanoparticles (NPs) activated by UV irradiation are known to have a bactericidal effect. In this study we report the details of TiOb>2b> NPs influence on the colony-forming capacity of E. coli in the dark at pH 4.0-4.5. At this pH the bacterial cells are negatively charged and TiOb>2b> NPs present a positive charge. A 60 min contact between E. coli with TiOb>2b> at concentrations of 0.02-0.2 mg/mL led to a reduction of E. coli cell number from 10⁸ to 10⁴ CFU/mL. After the reduction the system remains unchanged during the subsequent incubation. The observed reduction was a function on the initial E. coli concentration. In the presence of 0.04 mg/mL TiOb>2b> the colony-forming units (CFU) reduction after 60 min was of four-five orders of magnitude when the initial concentration was 10⁸ cells/mL. But when starting with an E. coli concentration of 10⁷ cells/mL the cell number reduction was less than one order of magnitude. Less than one order of magnitude cell number reduction was also observed for suspensions of E. coli 10⁸ cells/mL and 0.002 mg/mL of TiOb>2b>. The bacteria number reduction was always accompanied by the formation of cell aggregates. During cell incubation with TiOb>2b>, the pH of the suspension increased, but did not reach the TiOb>2b> isoelectric point (IEP). E. coli cells stained with the fluorescent dye acridine orange (AO) showed that the fluorescence of single cells remained unchanged after incubation in the presence of TiOb>2b>. The color change of fluorescence was revealed only in aggregated cells. This suggests changes in the physiologic state of E. coli incorporated into the aggregates. Aggregates of E. coli occur due to the electrostatic interaction between TiOb>2b> NPs and the bacterial cell surface. A hypothesis is suggested in this study to explain the CFU reduction and the retention of a certain irreducible number of cells capable of further division in the suspension in the presence of TiOb>2b> in the dark.