Journal of Photochemistry and Photobiology A: Chemistry 157 (2003) 81–85 Photocatalytic bactericidal effect of TiO 2 on Enterobacter cloacae Comparative study with other Gram (-) bacteria Jorge A. Ibáñez a , Marta I. Litter b,∗ , Ramón A. Pizarro a a Unidad de Actividad Radiobiolog´ ıa, Centro Atómico Constituyentes, Comisión Nacional de Energ´ ıa Atómica, Av. Gral. Paz 1499, 1650 San Mart´ ın, Prov. de Buenos Aires, Argentina b Unidad de Actividad Qu´ ımica, Centro Atómico Constituyentes, Comisión Nacional de Energ´ ıa Atómica, Av. Gral. Paz 1499, 1650 San Mart´ ın, Prov. de Buenos Aires, Argentina Received 30 December 2002; received in revised form 30 December 2002; accepted 24 January 2003 Abstract The bactericidal action of heterogeneous photocatalysis (UV-A/TiO 2 ) has been tested on Enterobacter cloacae, a microorganism very resistant to UV-A irradiation. Results have been compared with other representative strains of Gram (-) bacilli of different photosensitivity like E. coli, Pseudomonas aeruginosa and Salmonella typhimurium. The TiO 2 photocatalytic technology can inactivate bacteria resistant to oxidative membrane damage caused by direct UV irradiation, like E. cloacae, a common soil and aquatic microorganism, which normally is not affected by low UV-A irradiation intensity. In all cases, sublethal UV-A doses provoked an important lethality in the presence of TiO 2 . Inactivation rates of the microorganisms are compared and some clues on the mechanism of bacteria destruction are discussed. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Heterogeneous photocatalysis; TiO 2 ; Disinfection; Enterobacter cloacae; Gram (-) bacilli 1. Introduction Ultraviolet radiation deleterious effects on bacterial cells have been long recognized and its applications on antimi- crobial process have received great attention. The most energetic fraction of the ultraviolet spectra, corresponding to the UV-C range (200–290 nm), is commonly used as an antibacterial agent in water and air treatments, allowing effective disinfection rates by the employment of germici- dal lamps (254 nm). Furthermore, photo-induced bacterial inactivation caused by UV-A (320–400 nm) is well known and its lethal and sublethal effects have been studied by several workers [1–5]. Heterogeneous photocatalysis, an Advanced Oxidation Technology that uses UV and TiO 2 , has emerged in last years as an innovative method for water treatment. The potential applications of the technology in- clude organic matter degradation, abatement of metal toxic ions and water disinfection ([6–12] and references therein). Moreover, UV/TiO 2 has been proposed as one of the best disinfection technologies, because no dangerous (carcino- genic or mutagenic) or malodorous halogenated compounds ∗ Corresponding author. Tel.: +54-11-67727016; fax: +54-11-67727886. E-mail address: litter@cnea.gov.ar (M.I. Litter). are formed, in contrast with other disinfection techniques, e.g. those that use halogenated reagents. The antimicrobial activity of UV/TiO 2 has been es- sayed in several bacteria and viruses including Escherichia coli [10,16,17], Lactobacillus acidophilus [13], Serratia marcescens [10,16], Pseudomonas aeruginosa [16], Pseu- domonas stutzeri [18], Bacillus pumilus [19], Streptoco- cus mutans, Streptococus rattus and Streptococus cricetus (references in [12]), Streptococus sobrinus AHT [20], Deinococcus radiophilus [13,21], yeasts as Saccharomyces cerevisiae [13], algae as Chlorella vulgaris [13], and viruses such as phage MS2 [13,21,22], B. fragilis bacteriophage [13,21] and Poliovirus 1 [23]. Transparent TiO 2 films [24], TiO 2 immobilized in acetylcellulose membranes [14] and entrapment of TiO 2 into sol–gel prepared pellets [21] have been tested, and use of optical fibers [25] or intermittent and variable irradiation [21] have been also recommended to improve the application. Municipal wastewaters have been also treated with relatively good efficiency [26,27] and total and fecal coliforms and viruses present in secondary wastewater effluents have been successfully removed [23]. The technology can even be applied to destroy bioaerosols in air [28,29]. As TiO 2 photocatalysis can make use of the UV part of the solar spectrum, it becomes promis- ing to potabilize waters in developing tropical countries 1010-6030/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S1010-6030(03)00074-1