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Home / Equine Research Bank / Aust Vet J / Susceptibility pattern of bacterial isolates in equine ulcer...
Australian veterinary journal2022; 101(3); 115-120; doi: 10.1111/avj.13221

Susceptibility pattern of bacterial isolates in equine ulcerative keratitis: Implications for empirical treatment at a university teaching hospital in Sydney.

Abstract: Corneal ulceration is a common ophthalmic condition in horses. It is frequently caused by trauma to the corneal surface, followed by secondary infection by commensal or pathogenic organisms including Streptococcus equi subspecies zooepidemicus, Pseudomonas aeruginosa and Staphylococcus spp. Emerging antimicrobial resistance amongst these organisms has raised the need for appropriate antimicrobial therapy selection, to optimise treatment efficacy while minimising further antimicrobial resistance. Medical records of 38 horses presented at the University Veterinary Teaching Hospital Camden for ulcerative keratitis between 2010 and 2020 were reviewed to identify those with positive bacterial cultures and antimicrobial susceptibility profiles (13/38). Common susceptibility patterns were identified and used to guide the empirical treatment of equine bacterial corneal ulcers. Pseudomonas spp. (64.3%), Streptococcus equi subspecies zooepidemicus (14.3%) and Actinobacillus spp. (14.3%) were most commonly identified. Susceptibility to amikacin, gentamicin and ciprofloxacin was observed in 100%, 66.7% and 85.7% Pseudomonas spp. isolates respectively. Resistance to polymyxin B and neomycin occurred in 85.7% and 71.4% of Pseudomonas spp., respectively. All Streptococcus equi subspecies zooepidemicus organisms in this study were susceptible to ceftiofur, cephalexin, penicillin and ampicillin, while they were all resistant to gentamicin, neomycin, enrofloxacin and marbofloxacin. Predominating in this study, Pseudomonas spp. maintained overall aminoglycoside susceptibility despite some emerging resistance, and good fluoroquinolone susceptibility. High resistance to Polymyxin B could have arisen from its common use as first-line therapy for bacterial corneal ulcers. Although further research is required, these new findings about predominant bacteria in equine corneal ulceration in the Camden region and their antimicrobial susceptibility patterns can be used to guide the empirical treatment of bacterial corneal ulcers in horses.
© 2022 The Authors. Australian Veterinary Journal published by John Wiley & Sons Australia, Ltd on behalf of Australian Veterinary Association.
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Publication Date: 2022-11-25 PubMed ID: 36433648DOI: 10.1111/avj.13221Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The study examines the susceptibility and resistance patterns of bacteria involved in equine corneal ulcers, to assist in the selection of effective treatments. The research conducted on horses at a teaching hospital in Sydney revealed prevalent bacteria and the antibiotics they respond to, with some interesting findings on bacterial resistance to common therapies.

Context and Methodology

  • The study originates from the rising concern over antibiotic resistance in bacteria causing corneal ulceration, a common eye condition in horses. It is typically caused by an initial trauma to the corneal surface, resulting in secondary infection by opportunistic bacteria.
  • Bacteria traditionally associated with this condition include Streptococcus equi subspecies zooepidemicus, Pseudomonas aeruginosa and Staphylococcus spp.
  • The research involved a review of medical records from 38 horses that presented with ulcerative keratitis at the University Veterinary Teaching Hospital in Camden, between 2010 and 2020.
  • Positive bacterial cultures and their corresponding susceptibility profiles were obtained from samples collected from 13 out of the 38 cases reviewed. This data was then used to identify common susceptibility patterns, with the purpose of developing an empirical treatment for bacterial corneal ulcers in horses.

Key Findings

  • Pseudomonas spp. (64.3%), Streptococcus equi subspecies zooepidemicus (14.3%) and Actinobacillus spp. (14.3%) were the most commonly identified bacteria involved in this condition.
  • Pseudomonas spp. exhibited susceptibility to antibiotics like amikacin (100%), gentamicin (66.7%) and ciprofloxacin (85.7%). However, they showed resistance to polymyxin B and neomycin (85.7% and 71.4% respectively).
  • All isolates of Streptococcus equi subspecies zooepidemicus were found to be susceptible to antibiotics ceftiofur, cephalexin, penicillin and ampicillin. However, they showed universal resistance to gentamicin, neomycin, enrofloxacin and marbofloxacin.
  • The study suggested that the high resistance to Polymyxin B may have arisen from its frequent use as the first-line treatment for bacterial corneal ulcers in horses. Pseudomonas spp. maintained good susceptibility to aminoglycoside antibiotics and fluoroquinolones despite some emerging resistance.
  • The findings proposed that the observed patterns of antimicrobial susceptibility can be utilized for empirical treatment of bacterial corneal ulcers in horses in the Camden region.

Suggestions for Future Research

  • The research calls for further studies in order to consolidate the current findings and to continually update the clinical understanding of antibiotic susceptibility as resistance patterns evolve.
  • The study emphasizes the need to monitor emerging resistance, particularly amongst bacteria maintaining good susceptibility to aminoglycosides and fluoroquinolones, to ensure the ongoing effectiveness of empirical treatments.

Cite This Article

APA
Deniaud M, Tee E. (2022). Susceptibility pattern of bacterial isolates in equine ulcerative keratitis: Implications for empirical treatment at a university teaching hospital in Sydney. Aust Vet J, 101(3), 115-120. https://doi.org/10.1111/avj.13221

Publication

Australian veterinary journal
ISSN: 1751-0813
NlmUniqueID: 0370616
Country: England
Language: English
Volume: 101
Issue: 3
Pages: 115-120

Researcher Affiliations

Deniaud, M
  • School of Veterinary Science, University of Sydney, Sydney, New South Wales, Australia.
Tee, E
  • School of Veterinary Science, University of Sydney, Sydney, New South Wales, Australia.

MeSH Terms

  • Horses
  • Animals
  • Corneal Ulcer / drug therapy
  • Corneal Ulcer / veterinary
  • Polymyxin B
  • Hospitals, Animal
  • Ulcer / drug therapy
  • Ulcer / veterinary
  • Universities
  • Hospitals, Teaching
  • Keratitis / drug therapy
  • Keratitis / microbiology
  • Keratitis / veterinary
  • Anti-Bacterial Agents / therapeutic use
  • Anti-Infective Agents / pharmacology
  • Eye Infections, Bacterial / drug therapy
  • Eye Infections, Bacterial / microbiology
  • Eye Infections, Bacterial / veterinary
  • Gentamicins
  • Microbial Sensitivity Tests / veterinary
  • Streptococcus equi
  • Neomycin
  • Drug Resistance, Bacterial
  • Retrospective Studies
  • Horse Diseases / drug therapy

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Citations

This article has been cited 5 times.
  1. Stolle LM, Oltmanns H, Meißner J, Heun F, Schieder AK, Wolff HT, Ohnesorge B, Busse C. Polyhexanide, Povidone-Iodine, and Hypochlorous Acid Show High In Vitro Antimicrobial Efficacy Against Pathogens Commonly Associated With Equine Infectious Keratitis. Vet Ophthalmol 2026 Jan;29(1):e70141.
    doi: 10.1111/vop.70141pubmed: 41552904google scholar: lookup
  2. Yang L, Xie Y, Zhong G, Liu D, Zhu Y, Li J. Prevalence of antimicrobial resistance in equine-associated Pseudomonas aeruginosa: a systematic review and meta-analysis. BMC Vet Res 2025 Dec 22;22(1):44.
    doi: 10.1186/s12917-025-05190-0pubmed: 41430701google scholar: lookup
  3. Hardefeldt L, Thomas K, Page S, Norris J, Browning G, El Hage C, Stewart A, Gilkerson J, Muscatello G, Verwilghen D, van Galen G, Bauquier J, Cuming R, Reynolds B, Whittaker C, Wilkes E, Clulow J, Burden C, Begg L. Antimicrobial prescribing guidelines for horses in Australia. Aust Vet J 2025 Dec;103(12):781-889.
    doi: 10.1111/avj.70003pubmed: 40903020google scholar: lookup
  4. Iduu NV, Raiford D, Cohen ND, Landrock KK, Wang C. High-resolution melting curve FRET-qPCR rapidly distinguishes Streptococcus equi subsp. equi and zooepidemicus. Microbiol Spectr 2025 Sep 2;13(9):e0152925.
    doi: 10.1128/spectrum.01529-25pubmed: 40736350google scholar: lookup
  5. Wood J, King M, Dutton A. An assessment of bacterial transmission via rebound tonometry: An in vitro pilot study. Open Vet J 2024 Nov;14(11):3074-3079.
    doi: 10.5455/OVJ.2024.v14.i11.36pubmed: 39737021google scholar: lookup
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