TiO₂ Application for the Photocatalytical Inactivation of S. enterica, E. coli and M. luteus Bacteria Mixtures

Abstract

Water contamination by various bacteria, viruses and other pathogens is a great threat to human health. Amongst other Advanced Oxidation Processes TiO2 photocatalysis is considered as one of the most efficient treatment for the polluted wastewater disinfection. Usually, the wastewater produced by higher risk objects, such as hospitals, implicates diverse contaminants, but efficiency of most of the Advanced Oxidation Processes is tested by using only single pathogens and information on inactivation of bacteria mixtures is still limited. In this study, photocatalytical inactivation of three commonly found bacterial pathogens (gram-positive (Micrococcus luteus) and gram-negative (Salmonella enterica, Escherichia coli)) was investigated. Efficiency of traditional photocatalytic disinfection process using single bacterial pathogens was compared to the one observed for their mixtures. The impact of photocatalytical process parameters and treatment time on bacteria disinfection efficiency was studied. Photocatalytic disinfection efficiency testing with bacteria mixtures revealed, that in the presence of TiO2 photocatalyst and UV irradiation tested gram-positive cells were inactivated slower than gram-negative cells. Another important finding was that an overall photocatalytic disinfection efficiency of bacteria mixtures is not a straight forward sum of inactivation rates of individually tested pathogens but has a strong relationship to the properties of their competitive growth.

Synergistic Generation of Reactive Oxygen Species by Visible Light Activated TiO2 and S. Enterica Interaction

“…In our previous study [7] bacteria inactivation by UV light and 1 mg/ml of TiO2 at 23 °C temperature in 40 min reached more than 90 %. In current study we did not reach such high efficiencies and this could be related to the difference in temperature.…”

“…The amount of colony forming units and NPN uptake factor values are indicated as means ± standard deviation. Methods of statistical analysis are described in our previous publication Kuliesiene et al [7]. Tukey Test was used to pick out the significant differences within each group.…”

Photocatalytic Inactivation of Salmonella typhimurium by Floating Carbon-Doped TiO2 Photocatalyst

“…The cultivation of Gram-negative Salmonella enterica ser. Typhimurium SL1344 bacteria was performed by the procedure described in [ 34 ]. The only modification of the procedure was that after dilution to an OD 600 of 0.15, overnight bacteria culture was grown to an OD 600 of 0.7 instead of 0.8–1.0.…”

Influence of the Metabolic Activity of Microorganisms on Disinfection Efficiency of the Visible Light and P25 TiO2 Photocatalyst

“…Escherichia coli KMY strain cells were obtained from prof. Edita Suziedeliene (Institute of Biosciences, Vilnius University, Vilnius, Lithuania). Bacteria preparation and cultivation were performed following the procedure described in [30].…”

“…Our recent study [29] showed that under certain conditions the combination of gramnegative Salmonella enterica bacteria, visible light, and pristine P25 TiO 2 photocatalyst can provide an unexpectedly high disinfection efficiency, although under the same conditions photocatalytic bleaching of methylene blue solution was found to be negligible. Photocatalytic disinfection of bacteria mixtures by UV light activated P25 TiO 2 also indicated interesting behavior of the competing bacteria cells and showed a non-linear response [30]. To better understand the mechanisms behind the observed results, we performed in depth analysis of the role of bacteria metabolism in its response to the oxidative stress caused by pristine P25 TiO 2 photocatalysts and visible light.…”