Bactericidal Activity of Photocatalytic TiO ₂ Reaction: toward an Understanding of Its Killing Mechanism

Abstract

When titanium dioxide (TiO2) is irradiated with near-UV light, this semiconductor exhibits strong bactericidal activity. In this paper, we present the first evidence that the lipid peroxidation reaction is the underlying mechanism of death of Escherichia coli K-12 cells that are irradiated in the presence of the TiO2 photocatalyst. Using production of malondialdehyde (MDA) as an index to assess cell membrane damage by lipid peroxidation, we observed that there was an exponential increase in the production of MDA, whose concentration reached 1.1 to 2.4 nmol · mg (dry weight) of cells−1 after 30 min of illumination, and that the kinetics of this process paralleled cell death. Under these conditions, concomitant losses of 77 to 93% of the cell respiratory activity were also detected, as measured by both oxygen uptake and reduction of 2,3,5-triphenyltetrazolium chloride from succinate as the electron donor. The occurrence of lipid peroxidation and the simultaneous losses of both membrane-dependent respiratory activity and cell viability depended strictly on the presence of both light and TiO2. We concluded that TiO2 photocatalysis promoted peroxidation of the polyunsaturated phospholipid component of the lipid membrane initially and induced major disorder in the E. coli cell membrane. Subsequently, essential functions that rely on intact cell membrane architecture, such as respiratory activity, were lost, and cell death was inevitable.

Photocatalytic disinfection using titanium dioxide: spectrum and mechanism of antimicrobial activity

“…Most studies show that ROS are responsible for the killing, and various authors propose that ⋅OH are responsible (Ireland et al 1993;Kikuchi et al 1997;Maness et al 1999;Salih 2002;Cho et al 2004Cho et al , 2005Cho and Yoon 2008). Lipid peroxidation by ROS was demonstrated by the release of MDA as a breakdown product, and there was a concurrent loss of membrane respiratory activity measured by reduction of 2,3,5-triphenyltetrazolium chloride .…”

Removal of bioaerosols by the combination of a photocatalytic filter and negative air ions

“…Escherichia coli (Bioresource Collection and Research Center in Taiwan, BCRC 10675), Candida famata (BCRC 22304, a kind of yeast), and vir phage (BCRC 70193) were selected as the model strains of bacteria, fungi, and viruses, respectively. E. coli is a common rod-shaped bacterium with a particle size of about 0.78 m and is often selected as a challenge bioaerosol for germicidal tests (Keller et al, 2005;Lin & Li, 2003a, 2003bManess et al, 1999;Vohra et al, 2005Vohra et al, , 2006. C. famata is a frequently encountered airborne yeast with a particle size of about 2.44 m and has been selected as a challenge bioaerosol for germicidal tests (Lin & Li, 2003a, 2003b.…”

“…TiO 2 PCO has been applied for the purification of volatile organic compounds (VOCs) (Luo & Ollis, 1996;Yu & Lee, 2007; and for the disinfection of microbial contaminations in liquid phase (Cho, Chung, Choi, & Yoon, 2005;Christensen, Curtis, Egerton, Kosa, & Tinlin, 2003;Lee, Nishida, Otaki, & Ohgaki, 1997;Sunada, Kikuchi, Hashimoto, & Fujishima, 1998). Moreover, the mechanisms of PCO for the removal of microbial contaminations and VOCs have also been reported (Cho et al, 2005;Maness et al, 1999;Sunada et al, 1998;Yu & Lee, 2007;. Lin and Li (2003a) demonstrated that the effectiveness of a photocatalytic filter on the removal of bioaerosols was insignificant, which might be caused by a lack of enough time (on the order of 1 s) for the microorganisms to contact and react with the TiO 2 and reactive species generated by the PCO reaction.…”

Nanoparticles and the control of oral biofilms

“…The anatase form of nano-TiO 2 and UV light excitation are required to ensure maximum antimicrobial activity. TiO 2 photocatalysis is able to promote the peroxidation of the polyunsaturated phospholipid component of the microbial lipid membrane, induce loss of respiratory activity, and elicit cell death [80]. The study of Tsuang et al [81] demonstrated TiO 2 -mediated photocatalytic and bactericidal activities against obligate aerobes (P. aeruginosa), facultative anaerobes (S. aureus, E. coli, and Enterococcus hirae) and obligate anaerobes (Bacteroides fragilis).…”