Authors: Tukia Elina, Hallman Isa, Penttilä Maarit, Hänninen Satu, Kareskoski Maria
Journal: Frontiers in veterinary science
Summary
# Editorial Summary Endometritis remains a significant cause of mare infertility, with *Escherichia coli* and β-haemolytic streptococci frequently implicated; however, some bacteria exist in dormant states that evade both culture detection and antimicrobial therapy, complicating clinical management. Finnish researchers used chromogenic RNAscope® technology on formalin-fixed endometrial biopsies to localise *E. coli* 16S ribosomal RNA, comparing eight mares with positive bacterial cultures and moderate-to-severe inflammation, six with negative cultures but significant inflammation, and five healthy controls. Despite sensitive RNA in situ hybridisation techniques with fluorescence confirmation, the study detected only non-specific background signals with no morphologically characteristic bacterial rods in any sample, suggesting *E. coli* invasion of the lamina propria is uncommon or undetectable using this approach. The negative findings raise important questions about detection methodology: bacteria may persist as biofilms covering the epithelial surface, exist in highly localised foci, or be lost during tissue processing rather than genuinely absent from inflamed tissue. For practitioners managing chronic or recurrent endometritis, these results underscore the limitations of culture and conventional histology in identifying infectious causation, highlighting the need for alternative diagnostic approaches and challenging assumptions about the typical pathophysiology of bacterial endometritis.
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Practical Takeaways
- •Negative bacterial cultures in mares with endometritis do not rule out bacterial involvement; dormant bacteria and biofilms may persist despite negative results
- •E. coli-associated endometritis may involve surface biofilm rather than tissue invasion, suggesting traditional culture and histology may not detect the full extent of bacterial involvement
- •Current diagnostic and treatment approaches for endometritis may need revision to account for biofilm-forming bacteria that evade standard detection methods
Key Findings
- •No evidence of E. coli invasion into the endometrial lamina propria was detected using RNAscope and FISH methods despite positive bacterial cultures in 8 samples and inflammatory changes in 14 samples
- •Unspecific signals of limited size were detected randomly across all samples including controls, indicating lack of specific bacterial identification
- •E. coli may evade detection through biofilm formation, localized foci of infection, or loss during tissue processing rather than direct endometrial invasion