The placental microbiome

Microbiome populations have been well-characterized in many distinct body-sites.  Interestingly, there is a lack of knowledge in the microbiome of the placenta, an environment that was long thought to be sterile.  Investigating the placenta is important toward understanding the microbiome in human development, especially in light of previous evidence demonstrating that human microbiota populations fluctuate extensively in the first year(s) of life.  The placenta is the cradle of life for fetal development, leading researchers from Baylor School of Medicine to study the microbiome of this tissue.  Placenta samples were collected and analyzed to characterize the placenta microbiome, and explore links to fetal development and microbiome compositions. 

320 placenta specimens were collected, and PCR was used to characterize bacterial populations.  The Meta genome sequencing revealed that the placenta microbiome harbored unique abundances in specific bacteria compared to other body sites.  E. coli in particular had the highest species abundance.  Interestingly, the microbiota populations were most similar to the oral microbiome.  Species such as Prevotella tannerae and Neisseria, known to populate the mouth, were also abundantly present in the placenta.  Further analysis confirmed that the placenta bacteria were indeed most similar to bacteria specifically found in the tongue, tonsils, and gingival plaques. 

The researchers also demonstrated an association between placental microbiome composition and healthy births or births with complications.  Specifically, a significant association was shown between distinct placental microbiome populations and pre-term birth.  Taxa such as Durkholderia were shown to be enriched in the placentas of those who delivered their infants preterm, whereas Paenibacillus was abundant in normal terms placental specimens. 

This study reveals a couple very interesting associations between cross-site microbiome similarities and disruptions in compositions that appeared to be linked to preterm birth.  Although not definitive evidence, these findings could lead to some important research in the future.  There were a few confounding elements to this study, such as other body site samples occurred in non-pregnant subjects, or the fact that the mass of the placental microbiota was particularly low.  However, these findings certainly raise awareness of the uniqueness of the placental microbiome, and what this means in terms of the microbiome entering the developing fetus.  It will be interesting to see what further research can reveal about this relationship. 

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