Subscribe to the BioNews newsletter for free

Advanced Search

Search for

Like the Progress Educational Trust on Facebook



Placenta not sterile, bacteria gene study shows

28 May 2014

By Alice Plein

Appeared in BioNews 755

The placenta, which was long believed to be a sterile environment, is home to a community of microbes similar to those found in the mouth, researchers have discovered.

These microbes do not directly cause diseases. However the authors believe that changes to their community, referred to as a 'microbiome', might be a cause of common pregnancy complications such as preterm birth.

In the study, published in Science Translational Medicine, the researchers collected placental tissue from 320 women after delivery and analysed the DNA using an approach called shotgun metagenomics. This analysis revealed a gene expression pattern that suggested that a unique population of microbes lived within the placenta.

'We think this may be early evidence that the infant microbiome is populated before birth', said Dr Kjersti Aagaard, an associate professor of obstetrics and gynaecology at Baylor College of Medicine in Houston, USA, and a study author, told Bloomberg. 'We don't have direct evidence but it suggests that'.

The scientists also compared the composition of placental microbes to microbiomes found elsewhere in the mother's body. Such comparisons revealed strong similarities to the microbiome of the mouth. The authors suggest that microbes from the mouth are able to enter the bloodstream and travel to the placenta.

Certain types of microbe were more common in women who had given birth prematurely, a finding which supports previous studies where gum disease appears to raise the risk of preterm birth.

Dr Aagaard speculates that if oral bacteria do reach the placenta through the blood, then it is possible that diseased and bleeding gums could allow harmful bacteria to reach and colonise the placenta, potentially triggering premature birth.

Dr Aagaard is now beginning a larger study to explore this link by analysing the oral and placental microbiomes of more than 500 pregnant women at risk of preterm birth.

Professor Martin Blaser, director of the human microbiome programme at New York University, who was not an author on this paper, told the New York Times: 'I'm intrigued by the findings about the mouth and also the relationship with preterm labor'.

He added that pregnant women were often given antibiotics, 'for all kinds of reasons, many justified, but there's a slippery slope'.

'Assuming that the placenta was sterile anyway, doctors thought antibiotics would not affect the fetus. But if the placenta is not sterile, and is instead a portal for bacteria from the mother, what are the antibiotics doing?'

New Scientist | 21 May 2014
Scientific American | 21 May 2014
Baylor College of Medicine (press release) | 21 May 2014
Bloomberg | 22 May 2014
New York Times | 21 May 2014
Mail Online (Associated Press) | 21 May 2014
Science Translational Medicine | 21 May 2014


18 June 2012 - by Dr Louisa Petchey 
The most extensive catalogue of the trillions of microbes that live in and on humans - called the human microbiome - has been published by an international team of scientists...
11 July 2011 - by Dr Jay Stone 
Women with poor oral health take on average two months longer to conceive than those with healthy gums, Australian scientists have shown....
08 March 2010 - by Seil Collins 
Scientists have catalogued the genes of microbes living in our gut, information that could be crucial in assessing the impact of microbes on our health. The study, published in Nature, reports the sequencing of 3.3 million microbial genes, a gene set 150 times larger than the human genome....
17 March 2008 - by Dr Jess Buxton 
Several of the genes that influence lifespan in a type of worm do the same job in yeast, say US researchers, suggesting that they may also be involved in human ageing. A team based at the University of Washington in Seattle has discovered that 25 of...

Be the first to have your say.

You need to or  to add comments.

By posting a comment you agree to abide by the BioNews terms and conditions

- click here to enquire about using this story.

Published by the Progress Educational Trust


Public Conference
8 December 2017

Speakers include

Professor Azim Surani

Professor Magdalena Zernicka-Goetz

Professor Robin Lovell-Badge

Sally Cheshire

Professor Guido Pennings

Katherine Littler

Professor Allan Pacey

Dr Sue Avery

Professor Richard Anderson

Dr Elizabeth Garner

Dr Andy Greenfield

Dr Anna Smajdor

Dr Henry Malter

Vivienne Parry

Dr Helen O'Neill

Dr César Palacios-González

Philippa Taylor

Fiona Fox

Sarah Norcross

Sandy Starr


Good Fundraising Code

Become a Friend of PET HERE and give the Progress Educational Trust a regular donation