By Will Dunham
WASHINGTON, May 21 (Reuters) - The human placenta, the organ that nourishes a developing baby, is not the pristine place some experts had assumed.
Researchers said on Wednesday they have identified a relatively small but thriving group of microbes that inhabit the placenta alongside human cells in a finding that may point to new ways of spotting women at risk for pre-term births.
There were clear differences in the makeup of placental microbes, or microbiome, in women who had premature babies compared with those who delivered full-term babies, said Dr. James Versalovic, a professor at Baylor College of Medicine and head of pathology at Texas Children's Hospital in Houston.
Versalovic said this knowledge could lead to diagnostic tests to forecast which women may be at risk for pre-term birth and help obstetricians manage those pregnancies in new ways.
Scientists have known that microorganisms routinely reside in large numbers in certain parts of the human body such as the gut, which is naturally awash with bacteria.
The gut is one thing. But would the placenta, which forms within the mother's womb, provides oxygen and nutrients to the fetus and is pushed out after birth, also support a bunch of bacteria?
"This is a eureka moment where we say: 'Wow, there are bacteria here in the placenta,'" said Versalovic, who noted that the view among many experts had been that the placenta might be sterile, free of such microbes.
"Now we can begin to say: 'What are they doing? So why are the bacteria there?" Versalovic said in a telephone interview.
Over the eons, such colonies of microbes have been "co-evolving with humans," Versalovic said.
"This intimate relationship has resulted in the maintenance of a microbial community in the placenta during healthy pregnancies that clearly is not impacting the fetus in a negative way and may be helping to nourish the fetus, protect the fetus, enable the fetus to develop."
The researchers examined placental tissue collected in Houston from a diverse group of 320 women. DNA, both human and bacterial, was extracted from the placenta and sequenced using sophisticated techniques, said Baylor College of Medicine professor Dr. Kjersti Aagaard, another of the researchers.
More than 300 types of bacteria were detected in this placental tissue, with the well-known E. coli the most abundant, Versalovic said. The study found that this placental microbial population more closely resembled that of the mouth than other sites in the women such as the gut or vagina.
The microbial population in the placenta is more sparse than in other places such as the gut, the researchers said.
Aagaard said that, while the study found differences in the placental microbiome in women who had pre-term babies, there was no such difference in women who, for example, delivered via Caesarean section versus vaginal birth, or who were obese.
The study, part of a project funded by the U.S. National Institutes of Health to understand these microbes and their effect on health, was published in the journal Science Translational Medicine. (Reporting by Will Dunham. Editing by Andre Grenon)