Bacterial Isolates from Indolent Corneal Ulcers in Dogs

In the Literature

Levitt S, Osinchuk SC, Bauer B, Sandmeyer LS. Bacterial isolates of indolent ulcers in 43 dogs. Vet Ophthalmol. 2020;23(6):1009-1013.

The Research …

Indolent corneal ulcers (also referred to as superficial chronic corneal epithelial defects) are a common ocular problem in middle-aged and older dogs. This painful condition is recognized by its characteristic historical and clinical features. Indolent corneal ulcers tend to be chronic and appear as superficial corneal defects that are not associated with corneal stromal loss. A nonadherent ring of corneal epithelium surrounds the ulcer and produces an indistinct halo of fluorescein retention after the ocular surface is stained because of dye diffusion under the epithelium. Although corneal vascularization occurs in some dogs with indolent corneal ulcers, this finding is inconsistent.¹ Pathophysiology has not been fully elucidated, but there is evidence that the development and persistence of these defects results from a primary corneal healing abnormality and that they are not related to an infectious process.²

This study sought to determine whether bacteria could be isolated from the ocular surface in dogs with indolent corneal ulcers and whether isolation of bacteria influences clinical outcomes. Ocular swab samples were evaluated via aerobic and anaerobic bacterial culture. One or more bacteria were isolated from 8 of 43 dogs (19%) included in the study. Staphylococcus spp and Streptococcus spp were most commonly isolated. No difference in clinical outcome was detected between culture-positive and culture-negative indolent corneal ulcers. Following a procedure to encourage indolent ulcer resolution (eg, diamond burr debridement, grid keratotomy), both culture-positive and culture-negative groups had a similar healing rate and time to healing. 

The study did not find that isolation of bacteria significantly affected the healing rate of indolent ulcers; however, potentially pathogenic aerobic bacteria were identified in the corneas of affected dogs. After debridement, 4 dogs with culture-negative ulcers developed clinical complications, possibly as a result of opportunistic bacterial infection. This included 3 dogs with corneal stromal loss, which is a distinguishing characteristic of bacterial keratitis.³ Of the 4 dogs with complications, 2 required conjunctival pedicle graft surgery for ulcer resolution. Although infrequent, complications of indolent corneal ulcers potentially resulting from secondary bacterial infection have been reported in other studies, particularly after debridement procedures,^4,5 highlighting the importance of prophylactic topical antibiotic treatment in dogs with indolent corneal ulcers.

... The Takeaways

Key pearls to put into practice:

• Indolent corneal ulcers in dogs can be colonized by potentially pathogenic aerobic bacteria, most commonly Staphylococcus and Streptococcus spp.

• Isolation of bacteria from indolent corneal ulcers does not impact the clinical outcome in most dogs but can occasionally result in severe, globe-threatening corneal complications. Close clinical monitoring is advised until the ulcer heals.

• Prophylaxis with topical antibiotics that provide coverage for gram-positive bacteria is important to reduce the risk for severe complications associated with opportunistic bacterial infection.