The findings again reverse the absence of microorganisms in the placenta of healthy humans

Reporter Li Wei
The microbiome is distributed in many organs of the human body, a group invisible to the naked eye, and even determines the human intake of nutrients and the ability to resist disease. As a result, research into how microbes shape human health and growth has been extremely popular over the past few decades. When exactly did microbes "settle" in the human body? A new study by a team at the University of Cambridge in the UK, published online by Nature, shows that healthy human placentas are free of microbiomes. This conclusion is widely seen as the biggest reversal since 2014.pregnancy, human embryos begin to form an important organ, the placenta. The placenta is both the lifeline and guardian of the embryo, delivering oxygen, nutrients and immune molecules from the mother's blood to the developing fetus, as well as a barrier to infection. For more than a century, doctors have believed that, like fetuses and uteruses, the placenta has no microbes, otherwise there is a problem. Weaned babies, on the other than adults, have a complete microbiome.
An associate professor at Baylor College of Medicine in Houston, Texas, and colleagues reported in the journal Science Translational Medicine in 2014 that their study showed that while not every placenta contains detectable bacterial DNA, it is found in many placentas.
study found that the presence of microbiomes in the intestines at birth does not match the microbiome in the vagina of pregnant women, so it is speculated that there are other sources of microbiomes in the newborn's intestines, most likely the placenta.
also used macrogenome bird gun sequencing to analyze the microbial composition of 320 donated placentals and found that about 300 microbes were present in the placenta, although at lower levels. To obtain in-depth images of these microbial functions, the researchers sequenced a subset of the samples genome-wide. In most samples from this subset, they found that the largest number of placentas were common, disease-innocid E. coli in the intestines, and that the two oral bacteria, Tanner's Prevot's and Neisseria, were relatively large. When they compared the microbial DNA in the placenta with those common in other parts of the body, they found that it most consistent with the type of microbe in the mouth.
that oral microbes may first "slip" into pregnant women's blood and then migrate to the placenta to "settle." The study also found significant differences in the composition of the placental microbiome between premature fetuses and full-term fetuses, which may indicate a link between the placental microbiome and presate birth.fact, once published, the study of the higher people of Au has caused great controversy. Some researchers believe traces of placental microbes are "contaminants on DNA extraction kits used in research." The team at the University of Pennsylvania's Perelman College found trace traces of DNA on sterile gauze, reagents, DNA purification kits and other everyday devices, and the bacterial DNA they eventually extracted from six placental samples was indistinguishable from the DNA they found on the sample kit. Similarly, in the view of the Cambridge University team, the 2014 study was flawed, and their study showed that previous studies had suggested that bacteria present in the placenta were derived from laboratory contamination and metastasis during childbirth.
Team at the University of Cambridge analysed placental samples from 537 women, available through vaginal or caesarean sections, both healthy and unhealthy, the largest number of samples to date used in such studies.
team used an undiscovered bacteria in the human body, salmonella, to stimulate tissue as a positive control and then extract DNA. For 80 of these samples, the researchers used 16S rRNA gene sequencing and macrogenomic analysis. The macro genome, also known as the metagenome or ecological genome, refers to the sum of the genes of all microorganisms symbly living with humans. That is, 16S rRNA sequencing is for all bacteria conservative gene part, macro genomic analysis is to measure the sample of all the sequences of microbial genetic material, and then correspond to a specific strain.
for the rest of the samples, the researchers used two different DNA extraction kits in parallel, and then sequenced each sample by 16S to compare the results of the two kits.
the study found the presence of multiple microorganisms? In fact, when sequencing with different kits and reagent batches, the researchers could not find the existing microbial species. Vaginal Lactobacillus, for example, is present in the placenta samples of pregnant women who give birth, but the absence of caesarean section indicates that these microorganisms are attached to the placenta during childbirth, rather than living in the placenta before delivery, and infection during childbirth is the source of the microorganisms. Similarly, studies have found that some microorganisms in the placenta associated with vaginal inflammation are also "obtained" during childbirth.
in addition to being obtained from the outside world during childbirth, microorganisms may also come from the treatment of the placenta, which the researchers collected was washed and re-frozen in a salt solution, and the entire process was also contaminated with microorganisms. Then there's the process of extracting DNA, even from the sequencer. Recording different experimental times, operators, reagent batches, and sequencer, the researchers determined that these microbial contaminations were not caused by differences between different times, people, and equipment, but were common. This confirms previous reports that there is a relatively rich microbiome in the DNA extraction kit, and that the so-called microbiomes in the placenta actually come from after childbirth.
study at the University of Cambridge, streptococcus is the only bacteria found in the placenta, found in 5% of the samples and not from environmental pollution. Streptococcus is a pathogenic bacteria that can cause neonatal sepsis, pneumonia and meningitis, and its presence means that the placenta becomes infected in pregnant women. That is, the placenta should be sterile unless an infection occurs. Under normal physiological conditions, babies are extremely unlikely to get microbes from the placenta.
, a reproductive biologist at the University of Cambridge and one of the study's authors, said: "Overall, the results suggest that there are no microbes in the healthy placenta unless it is infected. Chinaalso stepping up research on microorganisms, such as China's
-focused deployment project "Common Technology Research on the Microbiome of Human and Environmental Health" and the "China
Microbiome Program" launched at the end of 2017. Liu Shuangjiang
director of the China Institute of Microbiology, has said that the microbiome's concern about heat is increasing. Among them, the greatest concern for the human health microbiome, especially in the digestive microbiome, has found that the gut microbiome and diabetes, liver disease, obesity, mental illness and other related, but also further put forward the digestive microbiome balance has an important impact on health of the new concept.
However, how to establish a symbous relationship between human hosts and their microbiomes remains an interesting but controversial issue, and the Cambridge University study also sets a benchmark for the study of microbiomes in other human organs or tissues, such as the lungs, blood, etc., do they carry small amounts of microbes? However, researchers such as Chanock say negative results are hard to prove, so further research is needed to find out if there are any microbes in the placenta.