Evidence Library / Condition guides
Condition guide · Dogs, cats and horses
Antibiotic-resistant keratitis: where UVC fits.
A guide for veterinary teams
34%
of canine keratitis isolates were multidrug-resistant in 2020, up from 5% in 2016 (US study, 476 dogs)
0
bacterial growth in mouse corneas infected with multi-drug-resistant Pseudomonas after UVC
5 s
of 265 nm UVC worked as well against MRSP and MDR E. coli as against susceptible strains in vitro
Multidrug-resistant bacteria are increasingly found in corneal infections, especially in referral cases. UVC acts on microbial DNA directly, so its effect doesn’t depend on antibiotic susceptibility, and published studies show it working against resistant strains.
What it is.
Bacterial keratitis in companion animals is most often caused by Staphylococcus pseudintermedius, β-haemolytic streptococci and Pseudomonas aeruginosa. A 2026 review in Veterinary Ophthalmology describes multidrug-resistant strains as increasing, especially in referral and specialty clinics, and calls resistance a current, clinically significant problem rather than a future risk.
Why it’s hard to treat.
- In a Midwestern US study of 476 dogs, multidrug resistance among isolates rose from 5% in 2016 to 34% in 2020. Staphylococci were the most often resistant (33%).
- Animals recently treated with topical antimicrobials are more likely to carry resistant bacteria.
- Standard susceptibility testing is based on systemic drug levels, so lab results may not predict how eye drops perform on the ocular surface.
- Culture results take days, so first-line treatment is empirical.
Where UVC fits.
UVC damages microbial DNA directly, so the resistance mechanisms that defeat antibiotics don’t protect bacteria from it. In mice with keratitis caused by a multi-drug-resistant Pseudomonas strain, UVC cleared the infection as effectively as the one antibiotic the strain was susceptible to. An independent Royal Veterinary College study using a prototype 265 nm device found 5-second exposures worked as well against MRSP and multidrug-resistant E. coli as against susceptible strains. In the 2026 clinical study, one 5-second PhotonUVC treatment cut bacterial load by a median 96.5%. The 2026 review lists ultraviolet-based approaches among the antibiotic-sparing strategies to develop alongside antibiotics.
What the evidence doesn’t show yet.
- Clinical outcome data, such as healing time and recurrence, in resistant infections are not yet published.
- The resistant-strain studies were laboratory and mouse studies.
- UVC treats only the surfaces it reaches, not the conjunctival fornices or deeper tissue.
Sources
- Veterinary Ophthalmology, 2026
- Sebbag L, Pe’er O. Antibiotics in veterinary ophthalmology: resistance, stewardship, and emerging antibiotic-sparing strategies
- Frontiers in Veterinary Science, 2020;7
- Hewitt JS, Allbaugh RA, Kenne DE, Sebbag L. Prevalence and antibiotic susceptibility of bacterial isolates from dogs with ulcerative keratitis in Midwestern United States
- Veterinary Ophthalmology, 2026;29(4):e70214
- Williams OJ, Dawson C, Fischer MC, Frosini SM. Assessment of ocular surface pathogen susceptibility to UVC light treatment with a novel prototype device: an in vitro study
About this guide
Written by Photon Therapeutics for veterinary professionals. It summarises published evidence and is not a substitute for clinical judgement. Photon Therapeutics makes the PhotonUVC Vet device.
The evidence.
Independent efficacy study · 2025
UVC against multi-drug-resistant Pseudomonas keratitis
Independent study: no bacteria grew from UVC-treated corneas, matching targeted antibiotics.
Veterinary clinical study · 2026
Single 5-second UVC treatment cuts bacterial load in dogs, horses and cats
Median 96.5% drop in bacterial count across 34 eyes at a UK referral hospital.
Laboratory efficacy study · 2025
Anti-biofilm efficacy of low-dose 265 nm UVC
15-second exposures killed 48-hour Pseudomonas biofilm within 4 hours.
Bring PhotonUVC Vet into your practice.
A 5-second, non-contact UVC treatment for corneal infections in dogs, cats and horses.