Effective light-activated photosensitizers for photoinactivation of microorganisms

Among the various groups of microorganisms, bacteria and viruses can cause critical and persistent infections in humans. 1-3 The bacterial organization in biofilms, besides providing a pronounced advantage on microorganism survival when compared with planktonic forms, also promotes the development of higher resistance to conventional antimicrobial treatments. 2 Viruses have generally a greater capacity for mutation, especially RNA viruses, as was demonstrated by SARS-CoV2 virus mutations. This high viral mutation rate promotes the development of their resistance to traditional antivirals and establishes the resistance behaviour in virus populations, decreasing their susceptibility to some drugs. 3 Antimicrobial photodynamic treatments (aPDT) can be an efficient therapeutic alternative to eradicate microorganisms through the combination of a photosensitizer molecule (PS), dioxygen (O2), and visible light to induce the formation of reactive oxygen species (ROS), as singlet oxygen (1O2), that leads to the cell death. 3-5 Having this in mind, water-soluble PS bearing cationic groups (e.g., porphyrin, chlorin, and phthalocyanine dyes) were synthesized, structurally characterized, and their aPDT efficiency towards bacteria (Gram-(-) bacterium Escherichia coli in planktonic and biofilm forms) and viruses (bacteriophage Φ6 or Phage Phi6, as a surrogate for RNA viruses) were assessed.