Microbial Profiling of Amniotic Fluid, Umbilical Blood and Placenta of the Foaling Mare.
Authors: Hemberg Elisabeth, Niazi Adnan, Guo Yongzhi, Debnár Viktória J, Vincze Boglarka, Morrell Jane M, Kútvölgyi Gabriella
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Determining whether the equine placenta harbours its own bacterial community remains contentious amongst researchers, particularly given that bacteria have been detected in amniotic fluid and umbilical blood without necessarily indicating foal pathology. Hemberg and colleagues used 16S rRNA sequencing to profile bacterial DNA from placental tissues, amniotic fluid and umbilical blood across 24 mares and foals, correlating findings with inflammatory markers (serum amyloid A, white blood cell counts and fibrinogen levels) to assess foal health status. Bacteria were cultured from only four amniotic fluid samples, whilst aerobic growth dominated umbilical blood isolates (18 of 21 positive samples), and placental microbiota composition remained relatively consistent across anatomical regions at the phylum level—dominated by Proteobacteria (42–46%) and Actinobacteria (27–30%)—though genus-level diversity varied; crucially, all foals maintained normal inflammatory markers, indicating healthy outcomes despite microbial presence. The findings underscore that bacterial colonisation of fetal compartments and placental tissues occurs in uncomplicated equine pregnancies without triggering systemic inflammation or clinical disease, yet the study design cannot definitively establish whether the placenta maintains a true resident microbiome or is simply colonised during parturition. For practitioners, this work reinforces that detecting bacteria in foal samples warrants careful clinical interpretation rather than immediate concern, though further longitudinal research comparing healthy and compromised pregnancies would strengthen understanding of when microbial presence becomes clinically significant.
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Practical Takeaways
- •Bacterial presence in amniotic fluid and umbilical blood of healthy foals does not necessarily indicate infection or poor health outcomes
- •Standard neonatal inflammatory markers (SAA, WBC, fibrinogen) may not reflect microbial colonization in fetal compartments; clinicians should not over-interpret bacteria culture results without clinical signs
- •Further research is needed to definitively characterize placental microbiota and distinguish colonization from contamination in equine pregnancies
Key Findings
- •Bacteria were isolated from 4 of 24 amniotic fluid samples, with all samples containing polymorphonucleocytes
- •Aerobic bacterial growth was found in 18 umbilical blood samples and anaerobic growth in 3 samples from healthy foals
- •Placental microbiota showed similar diversity at phylum level across all regions, dominated by Proteobacteria (42-46.26%) and Actinobacteria (26.91-29.96%)
- •All foals maintained normal systemic inflammatory markers (serum amyloid A <5 mg/L) despite bacterial presence in fetal compartments