Antibiotics in Veterinary Ophthalmology: Resistance, Stewardship, and Emerging Antibiotic-Sparing Strategies

Antimicrobial resistance (AMR) is a growing challenge in veterinary ophthalmology, particularly in cases of bacterial keratitis, where progressive stromal infection can threaten vision and globe integrity within hours to days. This review synthesizes current evidence on pathogen distribution, antimicrobial susceptibility profiles, multidrug resistance (MDR) prevalence, and determinants of nonsusceptibility in veterinary patients, highlighting the emerging role of antibiotic-sparing alternatives. Across contemporary studies, Staphylococcus pseudintermedius, β-hemolytic streptococci, and Pseudomonas aeruginosa are consistently among the most frequently isolated pathogens. The highest MDR burdens are reported in referral populations and among methicillin-resistant staphylococci worldwide. Feline data remain comparatively limited but show regional variability in resistance patterns, while equine studies reveal temporal shifts in isolate distribution and a rising prevalence of methicillin-resistant organisms in tertiary settings. Recent topical antimicrobial exposure is the most consistently identified predictor of reduced culture positivity and elevated resistance rates in subsequent ocular isolates, highlighting the importance of early microbiologic sampling and judicious antibiotic use. Interpreting antimicrobial susceptibility testing (AST) in ophthalmology remains challenging because clinical breakpoints are generally derived from systemic dosing regimens, despite substantially higher, albeit transient, drug concentrations being achieved at the ocular surface following topical administration. Moreover, the ocular surface microenvironment, including tear proteins, inflammation, biofilm formation, and concurrent serum therapy, may substantially influence antimicrobial activity and therapeutic response. The review concludes with practical ophthalmology-specific stewardship recommendations, a One Health perspective on resistant ocular pathogens, and a forward-looking discussion of antibiotic-sparing adjuncts within a broader multimodal strategy to preserve antimicrobial effectiveness.