ORIGINAL RESEARCH article
Front. Microbiol.
Sec. Systems Microbiology
Volume 16 - 2025 | doi: 10.3389/fmicb.2025.1535095
This article is part of the Research TopicInvestigating the Role of Microorganisms in Ecosystems and Their Interactions with the Humans, Animals, Plants, and Environment InterfaceView all 13 articles
The Effect of Topical Antibiotic or Antibiotic-Corticosteroid Treatment on the Ocular Surface Microbiota of Healthy Horses
Provisionally accepted
- 1College of Veterinary Medicine, University of Florida, Gainesville, Florida, United States
- 2University of Calgary, Calgary, Alberta, Canada
- 3University of Guelph, Guelph, Canada
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Information regarding the impact of topical antibiotics with or without corticosteroids on the microbiota of the horses' eyes is limited. This study aimed to describe the bacterial ocular surface microbiota in healthy horses and evaluate the effect of topical antibiotics or antibiotic-corticosteroid medication on the ocular surface microbiota. This was a prospective, randomized, longitudinal, blinded study in which one eye of 12 horses was treated 3 times daily for 7 days with neomycin, polymyxin B and bacitracin ophthalmic ointment (n = 6) or neomycin, polymyxin B and dexamethasone (n = 6). The contralateral eyes operated as untreated controls. These drug choices and dosing frequencies reflect standard treatment protocols commonly used for uncomplicated ocular surface and intraocular diseases in equine practice. The inferior conjunctival fornix of both eyes was sampled at baseline before antibiotic administration (day 0), on days 3, 7, 9, 14, and 30. The ocular surface microbiota was characterized by amplifying the V4 region of the 16S ribosomal RNA gene. Alpha-(richness and diversity) and beta-diversity (weighted and unweighted UniFrac distances) measurements of the ocular surface microbiota varied similarly after treatments starting on day 1, returning to baseline measurements by day 30. At baseline, the main phyla detected in the ocular microbiota was Proteobacteria, representing 75% relative abundance, followed by Firmicutes and Bacteroidetes. After treatments, Proteobacteria declined in all groups, and Firmicutes and Bacteroidete's relative abundance increased, returning to baseline levels on day 30. The main genera detected on the ocular surface on day 0 were Suttonella, Nicoletella, Pasteurella, and members of the family Moraxellaceae. After treatment, the relative abundance of this bacteria declined in all groups, returning to baseline levels on day 30, although some alterations were still present. Here we show that topical antibiotics administered with or without corticosteroids induce changes in the ocular surface of the horses' eyes, and the microbiota appears to return to baseline approximately three weeks after treatment discontinuation.
Keywords: antimicrobial, Bacteria, Conjunctiva, Equine, microbiome, Dexamethasone
Received: 26 Nov 2024; Accepted: 04 Jun 2025.
Copyright: © 2025 Martin de Bustamante, Plummer, Caddey and Gomez. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Caryn Plummer, College of Veterinary Medicine, University of Florida, Gainesville, 32608, Florida, United States
Diego E Gomez, University of Guelph, Guelph, Canada
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