Beyond nocardioform: Transcriptionally active microbes and host responses in equine mucoid placentitis.
Authors: van Heule Machteld, Verstraete Margo, Norris Jamie Kaj, Graniczkowsa Kinga Barbara, Scoggin Kirsten E, Ali Hossam El-Sheikh, Ball Barry A, De Spiegelaere Ward, Daels Peter, Weimer Bart C, Dini Pouya
Journal: Equine veterinary journal
Summary
# Editorial Summary: Nocardioform Placentitis—A More Complex Picture Than Currently Recognised Equine mucoid placentitis has long been attributed primarily to nocardioform bacteria, yet little has been known about the actual microbial communities involved or how they interact with placental tissue during infection. van Heule and colleagues employed dual RNA sequencing on 31 placentas (with and without placentitis) to characterise transcriptionally active bacteria and concurrent placental immune responses, supplemented by untargeted metabolomics to identify associated biochemical signatures. Rather than finding nocardioforms to be the sole culprits, the research revealed a polymicrobial infection pattern dominated by Amycolatopsis, Crossiella, Lentzea, Enterococcus, and Mycobacterium species, with infected placentas showing marked upregulation of inflammatory pathways alongside suppression of vascular development genes—a finding that helps explain the clinical presentation of placentitis and foetal compromise. Notably, specific microbial metabolites, particularly beta-D-fucose produced by Amycolatopsis and Lentzea, correlated strongly with both bacterial stress-response genes and host inflammatory mediators (CXCL14, IL15RA, IFIH1), suggesting mechanistic links between microbial metabolism and placental pathology. These findings challenge the diagnostic term "nocardioform placentitis" and indicate that broader molecular profiling protocols—beyond culture-based or targeted PCR approaches—are needed to guide treatment decisions and improve clinical outcomes in mares with suspected mucoid placentitis.
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Practical Takeaways
- •Current diagnostic protocols labeling all mucoid placentitis as 'nocardioform' are oversimplified; expanded microbial identification beyond nocardioform species is necessary for accurate diagnosis and management decisions.
- •Understanding that multiple bacterial species and their metabolites drive placental inflammation opens potential for targeted antimicrobial and metabolite-based interventions rather than broad-spectrum approaches.
- •Metabolomic biomarkers like beta-D-fucose may offer non-invasive diagnostic opportunities to identify placentitis cases earlier in pregnancy, improving outcomes for affected mares.
Key Findings
- •Nocardioform placentitis involves both nocardioform bacteria (Amycolatopsis, Crossiella, Lentzea) and non-nocardioform bacteria (Enterococcus, Mycobacterium), not solely nocardioform organisms as historically assumed.
- •Bacterial gene expression in affected placentas shows enrichment in ribosomal activity and metabolism pathways, while placental tissue demonstrates upregulated inflammatory pathways and downregulated angiogenic pathways.
- •Beta-D-fucose, a microbe-specific metabolite elevated in placentitis samples, correlates strongly with bacterial stress-adaptive and DNA repair genes, suggesting a mechanistic host-microbe interaction.
- •Significant correlations exist between specific microbial genes (mraW, rlmB, amy, afuA, cysC) and host inflammatory genes (CXCL14, IL15RA, TASL, IFIH1), implicating targeted immune responses.