Fast and total inactivation of Gram-negative Pseudomonas aeruginosa in suspensions at natural pH 5.9 has been achieved by photoelectrocatalyisis (PEC), using Ag-decorated TiO2 photoanodes onto transparent conducting indium tin oxide (ITO) under UVA irradiation. The assays were made with 100 mL of bacterial suspensions in an undivided cell equipped with a photoanode, a stainless steel cathode and Ag vertical bar AgCl (3 M KCl) as reference electrode. Total inactivation was obtained in only 5 min using coatings with 4 wt.% Ag, 25 mM Na2SO4 as the electrolyte and 1.70 V as applied bias potential. Comparative photocatalytic treatments reached total inactivation at much longer time, suggesting the crucial role of hydroxyl radicals in PEC. These oxidants, which were detected by electron spin resonance, attacked the outer cell wall very effectively, since the recombination of the electron/hole pairs photoinduced under UVA irradiation was reduced. As characterized by high-resolution transmission electron microscopy (HRTEM), the best synthesized Ag-TiO2 thin-film photoanode mainly contains anatase TiO2 nanopowder decorated with Ag nanoparticles of ca. 45 nm. Analyses by X-ray powder diffraction and UV/Vis spectroscopy were also performed. The potential use of PEC for bacterial disinfection was confirmed for the rod-shaped Gram-positive Bacillus atrophaeus, which was more slowly inactivated due to its different cell wall structure. Scanning electron micrographs of both bacteria showed that PEC induced a high roughness, cell lysis and accumulation of cellular debris.