Chlorin e6 mediated photodynamic inactivation for multidrug resistant Pseudomonas aeruginosa keratitis in mice in vivo

Following corneal epithelium scratches, mouse corneas were infected with the multidrug resistant (MDR) P. aeruginosa strain PA54. 24 hours later, 0% (for control group), 0.01%, 0.05% or 0.1% Chlorin e6 (Ce6), a second generation photosensitizer derived from chlorophyll, was combined with red light, for photodynamic inactivation (PDI). 1 hour or 2 days later, entire mouse eyes were enucleated and homogenized for counting colony forming units (CFU) of P. aeruginosa. For comparison, 0.1% Ce6 mediated PDI was started at 12 hours post infection, and 0.005% methylene blue mediated PDI 24 hours post infection. Clinical scores of corneal manifestation were recorded daily. Compared to the control, CFU 1 hour after PDI started 24 hours post infection in the 0.01% Ce6 and 0.05% Ce6 groups were significantly lower (more than one log₁₀ reduction), the CFU 2 days post PDI higher in the 0.1% Ce6 group, clinical score lower in the 0.1% Ce6 group at 1 day post PDI. These findings suggest that PDI with Ce6 and red light has a transient efficacy in killing MDR-PA in vivo, and repetitive PDI treatments are required to fully resolve the infection. Before its clinical application, the paradoxical bacterial regrowth post PDI has to be further studied.