Highly potent photoinactivation of bacteria using a water soluble, cell permeable, DNA-binding photosensitizer

ABSTRACT Antimicrobial photodynamic therapy (APDT) employs a photosensitizer, light, and molecular oxygen to treat infectious diseases via oxidative damage, with a low likelihood for the development of resistance. For optimal APDT efficacy, photosensitizers with cationic charges that can permeate bacteria cells and bind intracellular targets are desired to not limit oxidative damage to the outer bacterial structure. Here we report the application of brominated DAPI (Br-DAPI), a water-soluble, DNA-binding photosensitizer for eradication of both gram-negative and gram-positive bacteria (as demonstrated on N99 E. coli and B. subtilis, respectively). We observe intracellular uptake of Br-DAPI, ROS-mediated bacterial cell death via 1- and 2-photon excitation, and selective photocytotoxicity of bacteria over mammalian cells. Photocytotoxicity of both N99 E. coli and B. subtilis occurred at sub-micromolar concentrations (IC50 = 0.2 μM – 0.4 μM) and low light doses (5-minute irradiation times, 4.5 J cm−2 dose) making it superior to commonly employed APDT phenothiazinium photosensitizers such as methylene blue. Given its high potency and 2-photon excitability, Br-DAPI is a promising novel photosensitizer for in vivo APDT applications.