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PloS one2023; 18(9); e0291028; doi: 10.1371/journal.pone.0291028

Alterations of the bacterial ocular surface microbiome are found in both eyes of horses with unilateral ulcerative keratitis.

Abstract: Next generation sequencing (NGS) studies in healthy equine eyes have shown a more diverse ocular surface microbiota compared to culture-based techniques. This study aimed to compare the bacterial ocular surface microbiota in both eyes of horses with unilateral ulcerative keratitis (UK) with controls free of ocular disease. Conjunctival swabs were obtained from both ulcerated eyes and unaffected eyes of 15 client-owned horses with unilateral UK following informed consent, as well as from one eye of 15 healthy horses. Genomic DNA was extracted from the swabs and sequenced on an Illumina platform using primers that target the V4 region of bacterial 16S rRNA. Data were analyzed using Quantitative Insights Into Molecular Ecology (QIIME2). The ocular surface of ulcerated eyes had significantly decreased species richness compared with unaffected fellow eyes (Chao1 q = 0.045, Observed ASVs p = 0.045) with no differences in evenness of species (Shannon q = 0.135). Bacterial community structure was significantly different between either eye of horses with UK and controls (unweighted UniFrac: control vs. unaffected, p = 0.03; control vs. ulcerated, p = 0.003; unaffected vs. ulcerated, p = 0.016). Relative abundance of the gram-positive taxonomic class, Bacilli, was significantly increased in ulcerated eyes compared with controls (q = 0.004). Relative abundance of the taxonomic family Staphylococcaceae was significantly increased in ulcerated and unaffected eyes compared with controls (q = 0.030). The results suggest the occurrence of dysbiosis in infected eyes and reveal alterations in beta diversity and taxa of unaffected fellow eyes. Further investigations are necessary to better understand the role of the microbiome in the pathophysiology of ocular surface disease.
Copyright: © 2023 Julien et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Publication Date: 2023-09-08 PubMed ID: 37682941PubMed Central: PMC10490969DOI: 10.1371/journal.pone.0291028Google 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 research reveals that horses with a condition known as unilateral ulcerative keratitis, affecting only one eye, exhibit significant changes in the diversity and quantity of bacteria present not only on the surface of the affected eye, but also on the healthy eye.

Objectives of the Research

  • The primary goal was to compare the bacterial ecosystem on the ocular surface in horses affected by unilateral ulcerative keratitis (a damaging eye condition) with those in healthy horses.
  • The research utilized advanced Next Generation Sequencing techniques, which have previously revealed a greater diversity in eye-surface bacteria compared to traditional culture-based studies.

Research Methodology

  • The study took conjunctival swabs, samples from the surface of the eye, from 15 horses with unilateral ulcerative keratitis – from both the affected and unaffected eyes.
  • They also took swabs from one eye of 15 healthy horses to serve as a control group.
  • The samples’ genomic DNA was extracted and sequenced using an Illumina platform, targeting a specific bacterial region in the ribosomal RNA (16S rRNA).
  • The data were then analyzed using the Quantitative Insights Into Molecular Ecology (QIIME2) software.

Key Findings

  • The infected eyes had a significantly reduced species richness, or diversity, compared to the healthy eyes in the same horses.
  • The distribution of these species (sometimes referred to as species evenness) was, however, not significantly different.
  • The structure of bacterial communities differed significantly between the eyes of horses with the disease and those without.
  • The infected eyes had a higher relative abundance of Bacilli (a group of Gram-positive bacteria) and Staphylococcaceae (a family of bacteria which includes many harmful species) compared to healthy eyes, including the unaffected eyes of horses with the disease.

Implications and Future Research

  • The findings indicate that the bacterial ecosystem, or microbiome, on the surface of eyes affected by unilateral ulcerative keratitis is significantly altered.
  • This ‘dysbiosis’ in infected eyes and alterations in the bacterial diversity and abundance in the unaffected eyes complicate our understanding of the disease’s pathophysiology.
  • Further investigation is thus needed to fully understand the role the microbiome plays in this and other ocular conditions.

Cite This Article

APA
Julien ME, Shih JB, Correa Lopes B, Vallone LV, Suchodolski JS, Pilla R, Scott EM. (2023). Alterations of the bacterial ocular surface microbiome are found in both eyes of horses with unilateral ulcerative keratitis. PLoS One, 18(9), e0291028. https://doi.org/10.1371/journal.pone.0291028

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 18
Issue: 9
Pages: e0291028

Researcher Affiliations

Julien, Martha E
  • Department of Small Animal Clinical Sciences, School of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.
Shih, Johnathan B
  • Department of Small Animal Clinical Sciences, School of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.
Correa Lopes, Bruna
  • Department of Small Animal Clinical Sciences, School of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.
Vallone, Lucien V
  • Department of Small Animal Clinical Sciences, School of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.
Suchodolski, Jan S
  • Department of Small Animal Clinical Sciences, School of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.
Pilla, Rachel
  • Department of Small Animal Clinical Sciences, School of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, United States of America.
Scott, Erin M
  • Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America.

MeSH Terms

  • Horses
  • Animals
  • Corneal Ulcer / veterinary
  • RNA, Ribosomal, 16S / genetics
  • Keratitis
  • Eye
  • Face

Conflict of Interest Statement

The authors have declared that no competing interests exist.

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