Thirteen different commercial TiO2 powders with specific surface areas varying from 9 to 335 m(2)/g and with isoelectric points (IEP) from 3 to 7.5 were investigated for their catalytic activity in E. coli inactivation. The TiO2 samples zeta potential, attenuation sizes and isoelectric points (IEP) were measured by the electroacoustic method. The influence of the initial pH of the TiO2 suspension was followed during the bacterial inactivation. It was observed that TiO2 Degussa P-25 consisting of an anatase-rutile powder inactivated E coli with high kinetics that did not vary with the initial pH of the suspension. This was not the case for the other TiO2 samples used in this study. The IEP could be correlated with the catalytic activity of the commercial samples for most of TiO2 powders investigated. The lower the IEP of the TiO2, the lower the bacterial inactivation activity. By electron microscopy it is shown that the clusters of TiO2 Degussa P-25 are only in partial contact with E. coli K-12 (diameter 1 mu m). The reasons for this behavior are discussed in terms of the interaction of the E. coli with TiO2. (c) 2005 Elsevier B.V. All rights reserved.