Assessment of Ocular Surface Pathogen Susceptibility to Ultraviolet-C (UVC) Light Treatment With a Novel Prototype...

Assess in vitro efficacy of a device emitting 265 nm UVC light against bacteria isolated from veterinary infectious keratitis.

Twenty-seven clinically-derived bacterial isolates: Staphylococcus pseudintermedius (n = 10; including n = 2 methicillin-resistant Staphylococcus pseudintermedius [MRSP]), Staphylococcus aureus (n = 1), Streptococcus canis (n = 4), Escherichia coli (n = 4, including n = 2 multidrug-resistant isolates), Pseudomonas aeruginosa (n = 7) and Serratia marcescens. (n = 1), and three type culture strains (n = 1 E. coli, S. aureus, S. pseudintermedius) were lawn cultured. Prototype UVC device (2.50 mW/cm² intensity, 23 mm diameter beam) provided triplicate exposures at 1, 2, 3, and 5 s, and plates incubated (37°C, 16-20 h). All experiments were performed in duplicate (n = 6 treatment zones per timepoint, per isolate). Absence of growth in all exposed areas at any time demonstrated complete UVC inhibition; presence of growth was categorized as < 10 or ≥ 10 colonies.

UVC inhibition was complete in 11/30 isolates at ≤ 5 s exposure. Partial efficacy was seen in 18/19 remaining isolates at 5 s; ≥ 33% zones demonstrated absence of bacterial growth. Efficacy against MDR-MRSP and MDR-E. coli was comparable to susceptible counterparts. All P. aeruginosa were completely inhibited at ≤ 5 s; the S. marcescens isolate was least susceptible with ≥ 10 bacterial colonies within 50% zones after 5 s.

Five seconds of UVC exposure is sufficient to markedly reduce growth of most bacterial species, including MDR-isolates and completely inhibit P. aeruginosa in vitro. These findings support further controlled in vivo safety and efficacy studies of UVC as an adjunct to topical antibiotics in companion animal infectious keratitis.