Optimizing the Antibacterial Efficacy of Photoactivated Chromophore for Infectious Keratitis–CXL Treatment Parameters
Purpose
When treating bacterial keratitis, determination of the correct pathogen is often clinically challenging. The benefits of using PACK (Photoactivated chromophore for infectious keratitis)-CXL to treat corneal infections is that the treatment is not pathogen-specific. In an attempt to optimize the treatment parameters, we analyzed the effect of high intensity PACK-CXL on the bacterial killing rate in an in vitro model using Pseudomonas aeruginosa.
Methods
The killing rate of a known concentration of bacterias (Pseudomonas aeruginosa and Staphylococcus aureus) was analyzed for the following conditions: 1) preservative-free riboflavin, with UV-A irradiation @ 18 mW/cm2 for 5 minutes 2) preservative-free riboflavin, with UV-A irradiation @ 36 mW/cm2 for 2.5 minutes 3) riboflavin with preservatives, with UV-A irradiation @ 18 mW/cm2 for 5 minutes 4) riboflavin with preservatives, with UV-A irradiation @ 36 mW/cm2 for 2.5 minutes 5) riboflavin only, no UVA 6) riboflavin with preservatives, no UVA. We used 0.1% riboflavin in all experiments.
Results
The groups with preservative-free riboflavin showed a pathogen reduction (killing rate) of 2 log units with 18 mW/cm2 and of one log unit with 36 mW/cm2. The groups with riboflavine with preservatives showed a killing rate of 2 log units (98 %) at both irradiation levels.
Conclusion
The P. aeruginosa and S. aureus killing rate is intensity-dependent when using conventional riboflavin and intensity-independent when preservatives are added to the riboflavin solution. These findings will allow the generation of optimized riboflavin solutions for the treatment of bacterial keratitis.