Streptococcus canis sequence type 43 may be associated with treatment failure in dogs with corneal ulceration

To profile Streptococcus canis isolates obtained from corneal ulcers in dogs.

10 dogs.

Medical records were searched to identify dogs diagnosed with ulcerative keratitis by a veterinary ophthalmologist and having a positive corneal culture for S canis during the year 2020. For each case, clinical findings and outcome were determined, antimicrobial resistance and sensitivity panels were summarized, whole genome sequencing was performed, and isolates were typed using multi-locus sequence typing and genome-based proteome phylogenetic analysis.

10 S canis isolates were included from dogs diagnosed with ulcerative keratitis. Dogs were either treated surgically via keratectomy and conjunctival grafting (n = 6) or treated medically (4). Three of 10 corneas failed to heal and required enucleation (2/6 conjunctival grafts and 1/4 medically managed corneal ulcers). All three corneal ulcers that failed to heal were associated with S canis sequence type (ST) 43. Sequence types identified from successfully treated cases included ST8 (n = 1), ST50 (1), ST2 (2), ST27 (1), and ST15 (1). One ST43 isolate was obtained from a dog that healed following a conjunctival graft, however this was the only dog that received an oral antibiotic in addition to topical antibiotics.

Based on this small dataset, S canis ST43 may be associated with increased virulence and contribute to conjunctival graft failure and progressive corneal collagenolysis. The postoperative administration of an oral antimicrobial may protect against conjunctival graft rejection in dogs specifically due to S canis ST43.