Photodynamic InactivationMediated by Endogenous Porphyrinsof Corynebacterium diphtheriae in Planktonicand Biofilm Forms

Photodynamic inactivation (PDI) has emerged as a promising approach to combat bacterial infections by using light activation of photosensitizers to induce microbial death. This study investigated the potential of endogenous porphyrins produced by Corynebacterium diphtheriae as photosensitizers for PDI. Qualitative analysis revealed the presence of porphyrins in all strains studied, with coproporphyrin III predominating. The addition of 5-aminolevulinic acid (ALA) enhanced porphyrin production, as evidenced by increased fluorescence intensity. In addition, high-performance liquid chromatography with diode array and mass spectrometry detection analyses confirmed the presence of coproporphyrin III and protoporphyrin IX in all strains, and the ALA supplementation did not alter the porphyrin profiles. Quantitative analysis showed that strain-dependent coproporphyrin III levels were significantly increased with ALA supplementation. Additionally, biofilm formation was positively correlated with porphyrin production, suggesting a role for porphyrins in biofilm formation. Photoinactivation experiments showed that the strains responded differently to light exposure, with ALA supplementation, reducing the time required for significant CFU/mL reduction. In addition, biofilm survival exceeded planktonic cell survival, highlighting the challenges posed by biofilm structures with regard to PDI efficacy. Despite the variable responses observed, all strains exhibited a reduction in viability following light exposure, demonstrating the potential of endogenous porphyrins for antimicrobial photoinactivation applications.