Bacteria live even in healthy placentas, study finds

by Lauran Neergaard
In this study, researchers analyzed placental specimens from 320 subjects, providing an initial view of the human placental microbiome, which had not previously been studied in such detail. Credit: V. Altounian/Science Translational Medicine

Surprising new research shows a small but diverse community of bacteria lives in the placentas of healthy pregnant women, overturning the belief that fetuses grow in a pretty sterile environment.

These are mostly varieties of "good germs" that live in everybody. But Wednesday's study also hints that the make-up of this microbial colony plays a role in .

"It allows us to think about the biology of pregnancy in different ways than we have before, that pregnancy and early life aren't supposed to be these totally sterile events," said lead researcher Dr. Kjersti Aagaard of Baylor College of Medicine in Houston.

We share our bodies with trillions of microbes—on the skin, in the gut, in the mouth. These communities are called our , and many bacteria play critical roles in keeping us healthy, especially those in the intestinal tract. A few years ago, the government's Human Microbiome Project mapped what makes up these colonies and calculated that healthy adults cohabitate with more than 10,000 species.

Healthy newborns pick up some from their mother during birth, different bugs depending on whether they were delivered vaginally or by C-section.

What about before birth? There have been some signs that the process could begin in-utero.

This video is not supported by your browser at this time.
This animation describes the placental microbiome. Credit: Science/AAAS

But, "we have traditionally believed in medicine that the uterus is a sterile part of the human body," said Dr. Lita Proctor of the National Institutes of Health, who oversaw the microbiome project.

With the new research, "we realize that microbes may play a role even in fetus development," added Proctor, who wasn't involved in the work. "The results of this study now open up a whole new line of research on maternal and pediatric health."

Aagard's team earlier had studied the microbiome of the vagina, and learned that its composition changes when a woman becomes pregnant. The puzzle: The most common vaginal microbes weren't the same as the earliest that scientists were finding in newborns.

What else, Aagaard wondered, could be "seeding" the infants' ?

With colleagues from Baylor and Texas Children's Hospital, Aagaard analyzed 320 donated placentas, using technology that teases out bacterial DNA to evaluate the type and abundance of different microbes.

The placenta isn't teeming with microbes—it harbors a low level, Aagaard stressed. Among them are kinds of E. coli that live in the intestines of most healthy people.

This handout photo provided by the Baylor College of Medicine, taken May 20, 2014, shows Dr. Kjersti Aagaard in her laboratory at the Baylor College of Medicine in Houston. Aagaard's new research shows a small but diverse community of bacteria lives in the placentas of healthy pregnant women, and hints that the microbes may play a role in premature birth. (AP Photo/Agapito Sanchez, Baylor College of Medicine)

But to Aagaard's surprise, the placental microbiome most resembled bacteria frequently found in the mouth, she reported in the journal Science Translational Medicine. The theory: Oral microbes slip into the mother's bloodstream and make their way to the placenta.

Why does the body allow them to stay? Aagaard said there appears to be a role for different microbes. Some metabolize nutrients. Some are toxic to yeast and parasites. Some act a bit like natural versions of medications used to stop preterm contractions, she said.

In fact, among the 89 placentas that were collected after preterm births, levels of some of the apparently helpful bacteria were markedly lower, she said.

Aagaard is beginning a larger study to explore the link, planning to analyze the oral and placental microbiomes of more than 500 at risk of preterm birth.

More information: "The Placenta Harbors a Unique Microbiome," by K. Aagaard et al. Science Translational Medicine, 2014.

add to favorites email to friend print save as pdf

Related Stories

Recommended for you

Doctors who helped paralysed man walk seek new patients

1 hour ago

The Polish doctors who performed the revolutionary treatment that allowed a paralysed man to walk again said Wednesday they were looking for new candidates, as their patient described how the medical procedure has changed hi ...

Cause of ageing remains elusive

2 hours ago

A report by Chinese researchers in the journal Nature a few months ago was a small sensation: they appeared to have found the cause for why organisms age. An international team of scientists, headed by the ...

Newly discovered bacterial defence mechanism in the lungs

3 hours ago

A new study from Karolinska Institutet presents a previously unknown immunological mechanism that protects us against bacterial infections in the lungs. The study is being published in the American Journal of Respiratory an ...

Neutralising antibodies for safer organ transplants

Oct 21, 2014

Serious complications can arise following kidney transplants. If dialysis is required within the first seven days, then the transplanted organ is said to have a Delayed Graft Function (DGF), and essentially ...

User comments