Efficacy of 265 nm ultraviolet C light in the treatment of multi-drug resistant Pseudomonas aeruginosa keratitis in vitro and in an in vivo murine model

Background

This study evaluated the in vitro and in vivo efficacy of 265 nanometer (nm) ultraviolet C (UVC) light using 1.93 mW/cm² against multi-drug-resistant (MDR) Pseudomonas aeruginosa (P. aeruginosa) keratitis.

Methods

The effect of UVC light was studied on two clinical isolates of P. aeruginosa. Isolate 1 was ciprofloxacin-susceptible, and isolate 2 was MDR (but ceftazidime-susceptible). For the in vitro evaluation, P. aeruginosa isolates (100 μl, 1*10⁸ CFU/ml) were spread on Muller-Hinton solid agar surface and exposed to UVC light for 1, 5, 10, 15, and 30 seconds (s). For the in vivo study, the right eyes of C57BL mice were infected with the P. aeruginosa isolates (5 μL, 1*10⁸ CFU/ml) in two sets with isolates 1 and 2, respectively. The first set (n = 24) was randomized into four groups: a) untreated, b) UVC light 15 s exposure twice daily for two days, c) topical ciprofloxacin 0.3 %w/v twice daily for two days, d) topical ciprofloxacin 0.3 %w/v two-hourly for two days. The second set with MDR P. aeruginosa (n = 24) was treated similarly except for group d (which received topical ceftazidime 5 %w/v two hourly for two days). The left eyes were used to evaluate the safety of applied treatments without inducing infection. At 48 hours (hrs), eyes were enucleated and subjected to microbiological and histopathology analysis.

Results

In vitro, the UVC light exposure resulted in a clear inhibition area for exposures of 15 and 30 s. In the in vivo murine model, UVC light prevented overall clinical severity (p < 0.05) at 24 and 48 hrs by both isolates. Microbiological assessment at 48 hrs showed no growth of organisms in UVC light-treated corneas of either of the sets, similar to an observed treatment with ciprofloxacin (set 1) and ceftazidime (set 2).

Conclusion

265 nm UVC light showed an exposure-dependent in vitro bactericidal effect on P. aeruginosa. The in vivo studies showed that UVC light eliminated both strains of P. aeruginosa with an equivalent efficacy.