Potential of Photodynamic Inactivation with Porphyrins Against Planktonic and Biofilm Forms of Antibiotic-Resistant Wound Infection Pathogens

Antimicrobial photodynamic inactivation is of particular interest in the context of the global spread of antimicrobial resistance. Aim. Evaluation of the effect of porphyrins on planktonic and biofilm forms of wound infection pathogens during photodynamic inactivation in vitro. Methods. Objects: asymmetric water-soluble porphyrins containing heterocyclic fragments on the periphery of the porphyrin cycle: residues of benzoxazole (O-por), N-methyl benzimidazole (N-por) and benzothiazole (S-por). Microorganisms: planktonic forms (N=91): clinical isolates from wound discharge with a predominance of gram-positive microorganisms; biofilms (N=20). Irradiation parameters: light source — LED lamp (white light) 20 W, maximum luminous flux 1500–1800 Lm; exposure time: 10, 15, 30, 60 minutes. The bactericidal effect of porphyrins on planktonic forms was studied using the «sterile» stain method. The destructive activity of porphyrins to biofilms was assessed by changes in optical density. Results. Antibiotic resistance was determined in 84.9% of the strains (95% CI 65.3–97.5). Three porphyrin compounds provided a high level of lysis of 94.5% of antibiotic-resistant and antibiotic-sensitive strains (N=86; 95% CI 86.7–102.3) after 10 minutes of irradiation. Porphyrins did not have a bactericidal effect on 5.5% of the strains (N=5; 95% CI 14.9–25.9); 80% (N=4) of these strains were gram-negative microorganisms. The activity of S-por and N-por porphyrins ranged from weak biofilm destruction to no effect, and the absence of destructive activity was determined for O-por. Conclusions. Porphyrins have a pronounced bactericidal potential against planktonic forms of gram-positive pathogens of infectious diseases, including those with antibiotic resistance. Some types of molecules (N-por, S-por) led to weak biofilm degradation.