Antibacterial Photodynamic Therapy in the Near-Infrared Region with a Targeting Antimicrobial Peptide Connected to a π-Extended Porphyrin

The increase of antimicrobial resistance to conventional antibiotics is worldwide a major health problem that requires the development of new bactericidal strategies. Antimicrobial photodynamic therapy (a-PDT) that generates reactive oxygen species acting on multiple cellular targets is unlikely to induce bacterial resistance. This localized treatment requires, for safe and efficient treatment of nonsuperficial infections, a targeting photosensitizer excited in the near IR. To this end, a new conjugate consisting of an antimicrobial peptide linked to a π-extended porphyrin photosensitizer was designed for a-PDT. Upon irradiation at 720 nm, the conjugate has shown at micromolar concentration strong bactericidal action on both Gram-positive and Gram-negative bacteria. Moreover, this conjugate allows one to reach a low minimum bactericidal concentration with near IR excitation without inducing toxicity to skin cells.