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ANZCVS / EVA Clinical Papers: Antimicrobial susceptibility and resistance patterns of microbial flora residing on the ocular surface of horses with ulcerative keratitis

Talk Overview
Introduction: Ulcerative keratitis is a common condition in equine practice. The objective of this study was to investigate antimicrobial susceptibility and resistance patterns of microbial flora residing on the ocular surface of horses with ulcerative keratitis in the Hunter Valley, Australia.

Materials and Methods: Medical records of horses diagnosed with ulcerative keratitis from 2014 to 2020 were reviewed. Information was collected regarding age, sex, breed, clinical manifestations, prior treatment, outcome, microbial swab cytology, culture and antimicrobial susceptibility.

Results: Medical records from 123 horses were evaluated (124 eyes). Seventy-five samples yielded bacterial growth (60%) and four samples yielded fungal growth (3%). Seventy-two horses (58%) received topical antibiotic therapy prior to microbial swab culture, and of these horses, forty-one (57%) yielded bacterial growth. Gram positive (84%) organisms were more common than Gram negative (16%). The most commonly isolated organisms were Streptococcus spp. (49/85, [58%]), Bacillus spp. (10/85, [12%]), and Staphylococcus spp. (9/85, [11%]). Antimicrobial resistance was found towards ofloxacin (4/57, [7%]), chloramphenicol (14/65, [21%]), tetracycline (18/59, [31%]), tobramycin (31/58, [53%]), gentamicin (31/54, [57%]) and neomycin (39/65, [60%]).

Relevance to Australian clinical equine practice: Gram positive bacteria were the dominant microorganisms on the corneal surface of horses with ulcerative keratitis. Horses with ulcerative keratitis were resistant to one or more topical antimicrobials, most commonly aminoglycosides, tetracyclines and chloramphenicol. Knowledge of the microbial flora and their antimicrobial susceptibility for each geographical region is important for guiding empirical therapy and increasing the chance of a positive case outcome in horses with ulcerative keratitis.

Authors
Elizabeth James-Jenks , Dr Jessica Partlow, Dr Matthew Annear

Resources

#VetFest 2020
VetFest 2020
#VetFest 2020
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