Equine ulcerative keratitis in the Netherlands (2012-2021): Bacterial and fungal isolates and antibiotic susceptibility.
Authors: Verdenius Clara Y, Slenter Inge J M, Hermans Hanneke, Broens Els M, Djajadiningrat-Laanen Sylvia C
Journal: Equine veterinary journal
Summary
# Editorial Summary: Equine Ulcerative Keratitis — Microbial Isolates and Resistance Patterns in the Netherlands (2012-2021) Bacterial or fungal infection complicates roughly one-third to one-fifth of equine ulcerative keratitis cases, making accurate microbial identification and appropriate antimicrobial selection critical to preserving vision. This Dutch referral clinic retrospective analysed microbial cultures, susceptibility profiles and corneal cytology from 178 horses with ulcerative keratitis over a decade, comparing culture results with cytological findings and examining whether prior topical treatment selected for resistant organisms. Staphylococcus species dominated bacterial isolates (48%), followed by Streptococcus (16%), whilst Aspergillus accounted for 81% of positive fungal cultures; notably, acquired antibiotic resistance was common in both Streptococcus and Staphylococcus, with gentamicin resistance significantly associated with prior gentamicin exposure (p<0.001), though overall resistance rates remained stable across 2012–2017 versus 2018–2021 cohorts. Cytology proved unreliable for confirming bacterial or fungal infection (showing poor agreement with culture results), yet identified fungal elements in 6% of culture-negative cases, suggesting potential value as an adjunctive tool when mycotic keratitis is suspected but fungal culture returns negative. Clinicians should consider culture-guided therapy when feasible rather than relying on empirical treatment, remain cautious with repeated gentamicin use given resistance patterns, and recognise that cytology alone cannot exclude microbial involvement—emphasising the importance of appropriate sampling and culture submission in managing these sight-threatening cases.
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Practical Takeaways
- •Obtain bacterial and fungal cultures before starting topical treatment for ulcerative keratitis, as microbial infection occurs in >50% of cases and antibiotic resistance is common
- •Avoid repeated gentamicin use for topical treatment due to high rates of acquired resistance; consider culture-guided therapy and rotate antibiotic classes
- •When fungal cultures are negative but keratomycosis is clinically suspected, corneal cytology may provide additional diagnostic value and should not be discarded
Key Findings
- •Bacterial cultures positive in 36% of samples (n=67/187) with Staphylococcus (48%) and Streptococcus (16%) most common; fungal cultures positive in 20% (n=30/153) with Aspergillus species predominant (81%)
- •Acquired antibiotic resistance was common in Streptococcus and Staphylococcus species, with gentamicin resistance significantly more frequent in cases previously treated with gentamicin (p<0.001)
- •Poor agreement between cytology and culture results (bacterial p<0.001, fungal p=0.02), but cytology identified fungal elements in 6 of 104 negative fungal cultures
- •Incidence of acquired antibiotic resistance did not increase significantly between 2012-2017 and 2018-2021 cohorts