Investigating the Efficacy of Various Photosensitizers and Irradiation Strategies in Antimicrobial Photodynamic Inactivation on Different Types of Microbes

Antimicrobial photodynamic therapy is a method that utilizes photodynamic inactivation of microorganisms exposed to a photosensitizer irradiated by a specific wavelength, followed by the formation of reactive oxygen species and subsequent oxidative stress. In contrast to antibiotics, which are generally efficient against specific microorganisms, photodynamic inactivation exhibits efficacy against a wide range of bacteria, representing a promising and non-invasive alternative to treating infections caused by pathogens of different origins. This study compares the antibacterial efficacy of five different photosensitizers, including TMPyP, Protoporphyrin IX, PdTPPS4, Methylene Blue, and ZnPCS2, against eight representatives of various pathogens, including Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa, Gram-positive bacteria Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Enterococcus faecium, MRSA and Bacillus subtilis. An optimal irradiation protocol was developed based on growth curve measurements involving double irradiation. To induce the photodynamic effect, we utilized LED emitters with wavelengths of 414 nm and 660 nm, chosen to align with the photophysical properties of the photosensitizers. Additionally, the research included assessments of the radiation’s phototoxicity and the photosensitizers’ dark toxicity against specific microorganisms. The optical properties of the photosensitizers were analyzed using absorption spectrophotometry. The effectiveness of photodynamic inactivation was assessed by determining the minimum inhibitory and bactericidal concentrations. This study aimed to identify the most suitable photosensitizer for clinical application, considering the toxicity of the photosensitizer, the radiant exposure, and its efficacy in photodynamic inactivation.