The alarming level of antibiotic resistance in common pathogenic bacteria requires alternative methods for their control. In recent years, the photodynamic inactivation of microorganisms gained increased attention as an alternative to antibiotics in order to control bacterial diseases and to prevent the spreading of multiresistant bacteria. It has been shown that porphyrin derivatives, mainly those bearing positive charges, are excellent photosensitizers in photodynamic inactivation. In this study it was evaluated how the charge of the photosensitizer influences, per se, the inactivation of Escherichia coli. For that purpose, five cationic porphyrins (1a-5a) with identical meso substituent groups were used. The results show that singlet oxygen production, charge number, charge distribution, aggregation behaviour and molecular amphiphilicity are all important features that contribute to the photodynamic inactivation efficiency of the photosensitizer. (C) 2015 Elsevier B.V. All rights reserved.