Effects of Photoactivated Titanium Dioxide Nanopowders and Coating on Planktonic and Biofilm Growth of Pseudomonas aeruginosa

We exploited the ability of photocatalytic titanium dioxide (TiO2) as an agent for the biofilm control. Two photocatalytic systems were investigated: a 3 g L-1 suspension of TiO2 nanopowder in demineralized water and glass slides coated with a TiO2 thin film, achieved by sol-gel deposition. A running protocol for the photoactivation of TiO2 was set up using the dye rhodamine B. The microorganisms studied were Pseudomonas stutzeri, Pseudomonas aeruginosa and a Bacillus cereus-group as planktonic cells. P. aeruginosa biofilms were also studied at both the solid-liquid and the solid-air interface. The TiO2 nanopowder produced 1-log reduction of Bacillus sp. planktonic cells in 24 h, 2-log reduction of P. stutzeri planktonic cells in 30 min and 1-log reduction of P. aeruginosa planktonic cells in 2 h compared with non-photo-activated TiO2. TiO2 thin film produced almost a complete eradication of P. aeruginosa planktonic cells (initial concentration 10(8) cells mL(-1)) in 24 h compared to a 3-log reduction caused by UV-A light alone. In contrast, neither the photocatalytic treatment with TiO2 film nor that with TiO2 nanopowder had any effect on P. aeruginosa biofilms at all the interfaces investigated. Possible explanations for these findings, and for the discrepancy between this work and literature data, are discussed.