Placental, oral microbiomes may be similarly populated

The placenta, historically thought to be sterile, actually harbors a unique microbiome, say researchers at the Baylor College of Medicine in Houston, Texas. Notably, they found that the placental microbiomes they studied are most akin to the human oral microbiome, strengthening the proposed association between maternal dental health and certain fetal outcomes.

“The placental microbiome has not been robustly interrogated, despite recent demonstrations of intracellular bacteria with diverse metabolic and immune regulatory functions,” the researchers state in the study.

“We noted that the most abundant microbes in the mom’s vagina were not what populated the baby’s intestinal microbiome,” said Dr. Kjersti Aagaard, lead author, in a Baylor College of Medicine press release. “We reasoned that there must be another source ‘seeding’ the infant’s gut at birth, so we sought to examine the placenta.” 

Why send placentas to pathology?

The researchers examined a population-based cohort of placental specimens collected from 320 subjects. Their gene carriage patterns were compared to those of other human body sites-including the oral, skin, nasal, vaginal, and gut microbiomes-from nonpregnant controls.

Escherichia coli (E. coli) was the species with the highest abundance in most individuals. Prevotella tannerae and nonpathogenic Neisseria species, both species of the oral cavity, were also detected in highest relative abundance. 

These new findings may have implications regarding dental health during the prenatal period. “[This study] reinforces long-standing data relating periodontal disease to risk of preterm birth,” said Dr. Aagaard.

Aagaard K, Ma J, Antony KM, Ganu R, Petrosino, J, Versalovic J. The placenta harbors a unique microbiome. Sci Transl Med. 2014;(6):237ra65.