Bacterial Corneal Infections in Veterinary Ophthalmology
Fluorescein dye highlights a corneal ulcer on a dog’s eye. Corneal infections, particularly bacterial keratitis, are a common and serious ocular problem in veterinary patients. They cause significant pain and can progress rapidly, potentially leading to vision impairment or even blindness if not promptly and aggressively treated[1]. In fact, infectious keratitis is considered one of the most common and sight-threatening eye diseases in both human and animal ophthalmology[2]. Prompt recognition and treatment are critical to prevent irreversible damage to the eye.
Common Causes and Pathogens in Animals
In dogs, corneal ulcers are frequently associated with bacterial infection[3]. Studies indicate that approximately 71% of isolates are Gram-positive cocci, while 29% are Gram-negative rods[4]. The most commonly identified pathogens in canine corneal infections include Staphylococcus pseudintermedius, Streptococcus canis, and Pseudomonas aeruginosa[5]. S. pseudintermedius—a normal skin commensal—is often the predominant organism.
Other species show distinct infection patterns. In cats, bacterial keratitis may develop secondary to viral ulceration, often involving Staphylococcus and Streptococcus species. Horses are especially prone to post-traumatic corneal infections caused by Streptococcus equi subspecies zooepidemicus and Pseudomonas[6]. Additionally, fungal keratitis (commonly Aspergillus spp.) is frequent in equine eyes, adding complexity to treatment[7]. Across species, opportunistic flora can invade corneal wounds, making vigilant monitoring essential.
Diagnosis and Initial Treatment
Diagnosis is based on clinical examination and diagnostic testing. Corneal cytology and bacterial culture are standard tools to identify the pathogen[8]. Cytology provides immediate insight (e.g., Gram-positive cocci vs. Gram-negative rods), guiding the empirical antibiotic choice while awaiting culture results. Culture and sensitivity testing confirm the diagnosis and allow for targeted therapy once results are available.
Initial therapy typically involves broad-spectrum topical antibiotics administered very frequently. Combinations such as triple-antibiotic ointments (neomycin-polymyxin-bacitracin) or fluoroquinolone eye drops are commonly used[9]. The treatment is later refined according to culture results for precise antimicrobial coverage[10][11].
Aggressive Therapy and Importance of Compliance
Bacterial keratitis requires aggressive and consistent therapy. In severe cases, topical medication may be administered every 1–2 hours initially[12]. Additional therapies, such as anti-collagenase agents (serum, EDTA) and pain control with atropine or anti-inflammatories, are often incorporated. Owner compliance is critical — skipped doses or premature discontinuation can lead to ulcer progression and vision loss[13].
Veterinarians emphasize adherence to the treatment plan and may recommend hospitalization to ensure accurate dosing. Diligent compliance greatly improves healing outcomes, while poor compliance often necessitates surgical intervention.
Antibiotic Resistance: A Growing Challenge
Rising antibiotic resistance poses a major challenge in treating corneal infections. Many Staphylococcus pseudintermedius isolates are now methicillin-resistant (MRSP), similar to MRSA in humans[4]. In one study, 9% of isolates were methicillin-resistant and 20% were multidrug-resistant (MDR), with MDR rates climbing from 5% in 2016 to 34% in 2020[14]. This trend mirrors human ophthalmology, where superbugs increasingly complicate treatment[15][16].
This underscores the importance of antimicrobial stewardship—using culture-guided therapy and avoiding overuse of antibiotics. Emerging alternatives, including antimicrobial peptides, bacteriophage therapy, and cold atmospheric plasma, are being explored to combat resistant ocular pathogens[17].
Conclusion
Bacterial corneal infections are ophthalmic emergencies requiring rapid diagnosis, empirical treatment, and timely adjustments based on culture results. With prompt intervention, aggressive therapy, and strict compliance, most cases can heal successfully, preserving vision. However, growing antibiotic resistance emphasizes the need for collaborative and evidence-based management strategies to safeguard ocular health in veterinary patients.
References
- Corneal ulcers update in canine and feline pets
- Comparison of bacterial culture results in canine ulcerative keratitis
- Susceptibility pattern of bacterial isolates in equine ulcerative keratitis
- Equine Infectious Keratitis: Diagnosis and Treatment – VetFolio
- Treating corneal ulceration in dogs – Part 2: Deep ulcers