Antimicrobial activity of cationic water-soluble porphyrin against multidrug-resistant bacteria in biofilms and canine skin samples.

Multidrug-resistant (MDR) microorganisms pose a threat to animal health, particularly in integumentary diseases, which can be caused by multiple organisms and often manifest as biofilms, hindering treatment effectiveness. We evaluated the antimicrobial activity of antimicrobial photodynamic therapy (aPDT) using a water-soluble tetra-cationic porphyrin (4-HTMeP) against MDR bacteria cultured in biofilm and in mono and polyculture grown on canine skin samples. We utilized 4-HTMeP porphyrin against MDR Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus pseudintermedius. A non-cytotoxic concentration of 4-HTMeP (40 µM), previously shown to be effective in vitro against these bacteria cultured in solution, was employed. Biofilms were treated with 4-HTMeP and subjected to light irradiation for 30, 60, and 90 min. Monocultures on canine skin samples were treated with 4-HTMeP and irradiated for 30 (S. pseudintermedius), 60 (E. coli), or 60 and 90 min (P. aeruginosa). Polycultures of S. pseudintermedius and E. coli were treated with light for 60 and 90 min. The efficacy of aPDT was evaluated by plating light-exposed biofilms, mono and polycultures of bacteria obtained from skin samples exposed to light and kept in the dark. Colony-forming units were counted after 24 h of incubation at 37 °C. aPDT using 4-HTMeP reduced bacterial concentrations of S. pseudintermedius and E. coli biofilms. Additionally, it significantly reduced bacterial concentrations cultivated on skin samples, with a particular emphasis on S. pseudintermedius. These findings indicate that aPDT with 4-HTMeP is a promising alternative treatment against MDR bacteria in animal skin infections and should be further explored through in vivo research.