Variables to be considered when assessing the photocatalytic destruction of bacterial pathogens

Abstract

The current study sought to assess the importance of three common variables on the outcome of TiO(2) photocatalysis experiments with bacteria. Factors considered were (a) ability of test species to withstand osmotic pressure, (b) incubation period of agar plates used for colony counts following photocatalysis and (c) chemical nature of suspension medium used for bacteria and TiO(2). Staphylococcus aureus, Escherichia coli, Salmonella ser. Typhimurium and Pseudomonas aeruginosa were found to vary greatly in their ability to withstand osmotic pressure, raising the possibility that osmotic lysis may be contributing to loss of viability in some photocatalytic disinfection studies. Agar plate incubation time was also found to influence results, as bacteria treated with UV light only grew more slowly than those treated with a combination of UV and TiO(2.) The chemical nature of the suspension medium used was found to have a particularly pronounced effect upon results. Greatest antibacterial activity was detected when aqueous sodium chloride solution was utilised, with approximately 1 x 10(6) CFU mL(-1)S. aureus being completely killed after 60 min. Moderate activity was observed when distilled water was employed with bacteria being killed after 2h and 30 min, and no antibacterial activity at all was detected when aqueous tryptone solution was used. Interestingly, the antibacterial activity of UV light on its own appeared to be very much reduced in experiments where aqueous sodium chloride was employed instead of distilled water.

Bactericidal Effects and Mechanisms of Visible Light-Responsive Titanium Dioxide Photocatalysts on Pathogenic Bacteria

“…In previous studies, treating polluted air and water with TiO 2 -based photocatalysts achieved total destruction of a large number of organic and inorganic compounds (Ho et al 2006;Ranjit et al 2001;Wong et al 2006). Recently, research has extended to the potential application of TiO 2 -based photocatalyts in the treatment of pathogenic microbes, including bacteria, fungi, and viruses (Chen et al 2009;Ditta et al 2008;Foster et al 2011;Maness et al 1999;Cushnie et al 2009;Yao et al 2008); thus providing a new approach to disinfection.…”

Inactivation of Staphylococcus aureus and Escherichia coli in Water Using Photocatalysis with Fixed TiO2

“…When TiO 2 is irradiated with UV light, free hydroxyl ·OH radicals are generated which exhibit strong bactericidal activity (Rincón and Pulgarin 2003). Unfortunately, TiO 2 suspended in crude water exhibited considerably less feasibility in real application (Cushnie et al 2009). Conversely, methods of coating the TiO 2 onto the material in the crude water demonstrated better performance in antibacterial activities.…”

Comparison of solar/H2O2 and solar photo-fenton processes for the disinfection of domestic wastewaters

“…Although high light intensities shortened the time to obtain better inactivation efficiencies than low light intensities by only solar light (Rincón and Pulgarin, 2003), 4-log removal was achieved in 58 and 59 (Rincón and Pulgarin, 2004). Cushnie et al (2009) showed that peptide rich suspension media are not suitable for performing photocatalytic and photolytic disinfection experiments and attributed this partially to absorption of UV light by peptides. It can be stated that the presence of peptides and inorganic ions in wastewater reduced the light reaching the bacteria by absorption and the real disinfection effect of solar light at 200 W/m 2 and 500 W/m 2 did not occur.…”