Alterations of the bacterial ocular surface microbiome are found in both eyes of horses with unilateral ulcerative keratitis.
Authors: Julien Martha E, Shih Johnathan B, Correa Lopes Bruna, Vallone Lucien V, Suchodolski Jan S, Pilla Rachel, Scott Erin M
Journal: PloS one
Summary
# Editorial Summary: Ocular Surface Microbiota Changes in Equine Ulcerative Keratitis Previous culture-independent studies have revealed that healthy equine eyes harbour considerably more bacterial diversity than traditional culture methods detect, yet little is known about how this microbiota shifts during ocular disease. Martha *et al.* used next-generation sequencing of 16S rRNA genes from conjunctival swabs to characterise bacterial communities in both eyes of 15 horses with unilateral ulcerative keratitis and 15 healthy controls, analysing samples with quantitative ecological software. The ulcerated eyes showed significantly reduced bacterial species richness (Chao1 index, *p* = 0.045) compared with the unaffected fellow eye, whilst ulcerated and unaffected eyes both exhibited distinctly altered bacterial community composition relative to healthy controls—particularly elevated proportions of Bacilli and the family Staphylococcaceae. Notably, the unaffected fellow eye also demonstrated dysbiosis-associated changes in community structure, suggesting that unilateral keratitis may involve systemic or anatomical factors influencing the ocular microbiota bilaterally rather than purely localised infection. For practitioners, these findings underscore that ocular surface bacterial balance appears important in keratitis pathophysiology, potentially opening avenues for diagnostics or targeted antimicrobial strategies, though mechanistic understanding of microbiota shifts and causation remains incomplete and warrants further investigation.
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Practical Takeaways
- •Unilateral eye ulcers may involve systemic or bilateral ocular microbiome changes, not just local infection in the affected eye
- •Culture-based diagnostics will miss the microbiota complexity; consider that dysbiosis rather than single pathogen infection may underlie some keratitis cases
- •Even the unaffected eye shows microbiome alterations in horses with unilateral disease, suggesting monitoring both eyes and considering whole-animal factors in treatment
Key Findings
- •Ulcerated eyes showed significantly decreased bacterial species richness compared to unaffected fellow eyes (Chao1 q=0.045)
- •Bacterial community structure differed significantly between both eyes of horses with keratitis and healthy controls (p=0.003 to p=0.03)
- •Bacilli class bacteria were significantly increased in ulcerated eyes versus controls (q=0.004)
- •Staphylococcaceae family was increased in both affected and unaffected eyes of diseased horses compared to controls, suggesting bilateral microbiome alteration