In Vitro Efficacy Testing of TONS504-Based Photodynamic Antimicrobial Chemotherapy (TONS504-PACT) Under a 405-nm Light-Emitting Diode Against Antimicrobial-Resistant Bacteria Causing Canine Keratitis.

Abstract

OBJECTIVE: To evaluate the in vitro efficacy of photodynamic antimicrobial chemotherapy (PACT) using TONS504, a newly developed hydrophilic and cationic photosensitizer, under a blue light emitting diode (LED) against antimicrobial-resistant bacteria isolated from dogs with keratitis. METHODS: Three bacterial strains (i.e., methicillin-resistant Staphylococcus pseudintermedius, extended-spectrum beta-lactamase-producing Escherichia coli, and Pseudomonas aeruginosa), isolated from two dogs with keratitis, were used in this study after antimicrobial susceptibility tests. PACT using TONS504 (0.1-100 mg/L) was performed under a 405-nm LED at 30 J/cm(20 mW/cm, 25 min) against bacterial suspensions (1.0 × 10CFU). Bacterial strains that were unexposed, exposed to TONS504 only, or exposed to blue light only served as controls. Antimicrobial effects were assessed by calculating the survival fraction based on the assessment of colony-forming units (CFU) on agar plates. RESULTS: Exposure to TONS504 or blue light only did not decrease the bacterial survival fraction against any of the strains. After TONS504-PACT under blue light against S. pseudintermedius, no colonies were observed at any TONS504 concentration, resulting in an approximate reduction of 2.3 × 10in the survival fraction. TONS504-PACT under blue light against E. coli and P. aeruginosa at 10 mg/L of TONS504 showed the greatest reduction in survival fraction, and the reduction was substantially lower than those of the respective controls. CONCLUSIONS: TONS504-PACT under blue light exhibited satisfactory activity against antimicrobial-resistant bacteria in vitro. Further research on the safety and clinical efficacy of TONS504-PACT under blue light is required; however, it is a potential treatment for antimicrobial-resistant bacterial keratitis in veterinary ophthalmology.