Study counters notion that placenta is sterile, suggests oral hygiene may be important for healthy pregnancy
Researchers have discovered a small community of bacteria living in a most unlikely place: the placenta, the organ that nourishes a developing fetus through the umbilical cord. The finding overturns the conventional wisdom that the placenta is sterile. The study also suggests that these microbes may come from the mouth, affirming that good oral hygiene may be important for a healthy pregnancy.
Medical experts have long assumed that any bacteria found in the organ must have been picked up when it passed through the vagina after delivery. But more recently, researchers have realized that a baby has a community of bacteria in its gut when it is born. And these bacteria don’t match those in the vagina, suggesting some other source, such as the placenta, says fetal medicine specialist Kjersti Aagaard of Baylor College of Medicine in Houston, Texas.
Aagaard and co-workers are collaborators on the U.S. Human Microbiome Project, which is studying microbiomes—communities of bacteria, fungi, and viruses—that live in various places on and in our bodies. They looked for a placental microbiome by analyzing carefully collected placentas from 320 pregnancies. The researchers extracted DNA from the placentas and sequenced it for snippets and entire bacterial genomes in order to identify and quantify microbial species and the genes they carried. This analysis revealed low levels of a diverse set of bacteria, mostly nondisease causing strains of Escherichia coli, which dominate our intestinal tracts, but also others from five broad groups, or phyla. Most were benign species known to provide services such as metabolizing vitamins.
Surprisingly, the mix of bacteria in the placenta looked more like the microbiome in an adult human’s mouth than the vaginal, skin, gut, or other body microbiomes, Aagaard’s team reports today in Science Translational Medicine. The researchers think the microbes may get to the placenta from the mother’s mouth through her bloodstream, perhaps when she brushes her teeth and dislodges them into the blood. That possibility is intriguing, because there’s a well-known correlation between gum disease and preterm birth. Indeed, the array of bacteria in the placenta differed in women who gave birth early, before 37 weeks.