AUG 01, 2019 5:43 PM PDT

The Human Placenta is Bacteria-Free

WRITTEN BY: Tiffany Dazet

A research team from the University of Cambridge has finally answered a heavily disputed question about the presence or absence of a microbiome in the human placenta. Scientists have traditionally viewed the placenta as sterile, with the assumption that the presence of microbes would endanger a pregnancy. However, a 2014 study suggested the presence of a unique microbiota in the placenta similar to bacteria found in human mouths. This most recent study, published in Nature this week, provided evidence that in healthy pregnancies, the human placenta does not contain microorganisms. Additionally, it’s unlikely that infants develop their microbiota in utero.

The research team analyzed 537 placenta samples, representing the largest sample size for a study of this kind. They used Salmonella bongori, which does not occur in humans, as a positive control. They used two DNA sequencing methods; the first of which targeting genes common to all bacteria. The second method used all DNA present in the sample and mapped it to specific bacterial and animal species. They discovered that any present bacteria were acquired during labor and delivery and that certain microbes occur in higher concentrations if a woman had a vaginal delivery versus cesarean section. 

After accounting for contaminants, the one bacterium that researchers found in 5% of the samples was Streptococcus agalactiae. According to a news article in Nature regarding the study, S. agalactiae can be transmitted from mother to infant during the birthing process and may cause pneumonia, septicemia, and meningitis.

Kjersti Aagaard, obstetrician and maternal-fetal medicine specialist at Baylor College of Medicine and Texas Children’s Hospital, disagrees with these results. Aagaard was also the lead author on the 2014 study that discovered the unique placental microbiome. Mainly, Aagaard disagrees with the researchers’ choice to disregard placental microbes that overlapped with those found in the vagina. As she stated to Science News, “why would we disregard and toss them out, when the biology makes perfect sense?”

Nature concludes that this “carefully controlled, large-scale study was needed to provide strong evidence for the absence of bacteria in the placenta.” While the author recommends further investigations, they state that we should feel confident that “the placenta is not a microbial reservoir and therefore is not a major direct stream of diverse microbes to the fetus under healthy conditions."

Sources: Nature (News & Views), Nature, Science News 
 

About the Author
  • Tiffany grew up in Southern California, where she attended San Diego State University. She graduated with a degree in Biology with a marine emphasis, thanks to her love of the ocean and wildlife. With 13 years of science writing under her belt, she now works as a freelance writer in the Pacific Northwest.
You May Also Like
JUN 07, 2020
Microbiology
JUN 07, 2020
Infants Exposed to Antibiotics are at Greater Risk for Childhood Obesity
The human gut hosts a huge community of microbes, potentially even before birth, which helps us digest and absorb nutrie ...
JUN 11, 2020
Clinical & Molecular DX
JUN 11, 2020
Glowing Chemical Reactions Could Put an End to Bad COVID Tests
  Advancements in diagnostic technologies are paving the way for the next generation of ultra-sensitive serological ...
JUN 18, 2020
Health & Medicine
JUN 18, 2020
People Taking Medicinal Cannabis Report Greater Well-Being
Legalization of medicinal cannabis is now fairly widespread, yet there's been a paucity of data collected on patient exp ...
JUN 25, 2020
Cancer
JUN 25, 2020
Examining the Glioma Influenced Immune System
The human body is a complicated network of systems and signals.  Many systems regulate themselves or others in vari ...
JUL 03, 2020
Cell & Molecular Biology
JUL 03, 2020
A Gut Pathogen Moves With Help From Its Environment
Campylobacter jejuni is a foodborne bacterial pathogen that causes millions of cases of food poisoning each year.
JUL 07, 2020
Microbiology
JUL 07, 2020
Why Some Are Naturally Better at Preventing Urinary Tract Infections
Urinary tract infections can be very painful and can cause nausea, chills, and fever. A pathogenic strain of E. coli is ...
Loading Comments...