"Nature" sub-Journal: Scientists are so hard!

Regarding the question of whether there are bacteria in the intestines of newborns, we finally have a definite answer
.

Recently, a research team led by Thorsten Braun of the Charité School of Medicine in Berlin, Germany and Deborah M.
Sloboda of McMaster University in Canada published an important research result in the journal Nature Microbiology[1]
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They immediately collected meconium with a rectal swab when the buttocks of the cesarean baby were exposed, so that the prenatal meconium was collected, and the contamination of maternal microorganisms was avoided to the greatest extent
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Their research results show that healthy babies do not colonize microbes in the intestines before birth, and the microbial spectrum of newborn meconium reflects the flora obtained at and after birth
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Regarding this discovery, Sloboda believes[2] "Infants' intestinal colonization occurs during and after their birth, which means that it is not only vulnerable to early environmental influences, but may also provide a potential window of intervention
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" Meconium collection Method schematic diagram The establishment and composition of neonatal intestinal flora has a direct impact on the maturation and development of the intestinal immune system and the metabolic function of the intestine
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In addition, neonatal enterobacteria are also related to certain acquired diseases or chronic diseases, such as obesity and asthma [3, 4]
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There are also some strains that can fight against the infection of other intestinal pathogens during the growth process and maintain the stability of the intestinal flora [5]
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In this way, early harvest of high-quality intestinal flora seems to make your health win at the starting line
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However, scientists still have disputes about where this starting line is
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Does the baby's intestines already contain the mother-derived flora before birth? What is its composition? Only by clarifying these problems can we better study the mechanism of infant intestinal flora on the later health status
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Although scientists have detected bacterial DNA in the placenta and amniotic fluid [6, 7], this still cannot prove that these bacteria can enter the baby's body during pregnancy, and because the measured amount of bacteria is extremely low, the possibility of contamination cannot be ruled out.

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In addition, some studies reflect the intestinal flora obtained from the mother before the baby is born by collecting the neonatal meconium (neonatal meconium) and analyzing the structure of its flora [8, 9]
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However, the source of these flora is not clear.
It may be contamination of the mother's reproductive tract, feces, skin, or even air, surgical instruments, and bed sheets
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In addition, studies have shown that the amount of bacteria in the first defecation of newborns is positively correlated with the time of defecation after birth [10], which implies that the microflora structure of the first feces of newborns is susceptible to the influence of acquired microorganisms
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Therefore, the problem of contamination and unreasonable sample collection methods make the composition of the neonatal flora before birth remain a mystery
.

Screenshot of the paper In order to answer this question more accurately, Katherine M.
Kennedy et al.
designed a research method to collect fetal meconium.
This method uses rectal swabs to collect babies born in cesarean section and breech.
Feces
.

Since the baby does not pass through the reproductive tract and the head is still in the mother's body, the bacteria in the reproductive tract and mother's feces will not enter the intestinal tract through the baby's mouth during the birth process, so the collected samples reflect the intestinal tract of the prenatal baby Flora
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Researchers really took great pains to study the intestinal bacteria in newborns, and we also want to thank these pregnant mothers and cute babies for their contributions to scientific research
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As a control, the researchers also recruited a group of pregnant mothers to collect the first fecal samples of the newborns in order to compare the flora structure of the two types of samples
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In addition, in order to minimize the pollution during the production process, medical staff have carried out stricter disinfection on the utensils and bed sheets used in the production
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The obstetrician also collected the skin flora, blood, body fluid, and air samples from the wounds of the mothers before and after the caesarean section, as well as the infant stool samples of the babies who were growing up
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The scientists finally used the meconium samples of 20 cases of cesarean section and 14 cases of first fecal samples of newborns (9 cases of natural delivery, 8 cases of cesarean section)
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The average age of all mothers at childbirth and the average weight of their newborns were roughly the same, and the pregnancy duration of the two experimental groups was not much different
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Researchers on the basic information of pregnant mothers and newborns cultured some samples under aerobic or anaerobic conditions
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The remaining samples were subjected to 16S rRNA sequencing to determine the composition and relative content of the flora
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After 120 hours of incubation, no viable bacteria growth was observed in 7 meconium samples, whether under aerobic or anaerobic conditions
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The other 13 meconium samples grew 1-2 strains of viable bacteria during the culture process, of which Staphylococcus epidermidis was the most common, and it also contained Staphylococcus lugdunensis and Staphylococcus saprophyticus.
Staphylococcus saprophyticus), Propionibacterium avidum (Propionibacterium avidum), Propionibacterium acnes (Propionibacterium acnes)
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However, these strains were also cultured in the mother's skin samples.
Since no characteristic strains commonly found in feces were found, they are more likely to come from skin contamination at the time of sampling
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The results of 16S rRNA sequencing showed that the number of gene sequence fragments in meconium samples was extremely low, and the human body's own gene fragments accounted for a large portion
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After removing the DNA sequence fragments of eukaryotic cells, the average number of gene fragments belonging to bacteria is only 76.
5, which is similar to the gene fragment composition of the blank control (sample containing only sequencing reagents)
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In addition, the researchers analyzed the sequence fragments of the meconium samples and found that the bacterial diversity represented by these fragments was also extremely low, and there was no difference from the blank control, which also showed that the bacteria in the meconium was most likely caused by the contamination of the reagent
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The number of bacterial gene sequence fragments and flora diversity in the first feces of newborns tested at the same time are very high, which is more consistent with the diversity and composition of the flora in the feces of young children during growth
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The similarity analysis of the structure and diversity of blank control, meconium, first feces of newborns, and feces of infants.
So which strains did 16S rRNA sequencing detect from meconium samples? Researchers analyzed the data and found that all 20 samples contained Halomonas sequences, 19 samples contained Rhodanobacter sequences, 15 contained Pseudomonas strains, and 3 contained large intestine.
Escherichia/Shigella
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It is worth noting that the above-mentioned strains were also detected in the blank control sample
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Researchers only detected Bacteroides and Staphylococcus that were not present in the blank control sample in a small number of samples (4 out of 20), but the accuracy of the detection results was not high, such as the same It is not always possible to detect a certain strain of a sample twice, or it requires a high number of PCR amplification cycles to detect it
.

The results of aerobic or anaerobic culture and 16S rRNA sequencing showed that most of the strains that appeared in meconium were bacteria on the mother’s skin or contamination of reagents during the sequencing process, and only Bacteroides was the only possible presence in a small number of fetuses.
Strains in the fecal sample, but the amount of bacteria is very low
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These results indicate that the baby’s intestine is almost a sterile environment from in the mother’s womb to before birth, and the mother cannot pass the flora to the fetus during pregnancy, and it is the neonatal flora that is established during the process of delivery.
The beginning of the critical period, and as the child grows, the difference in flora is getting bigger and bigger
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Of course, the study also has some shortcomings, such as the lack of samples such as amniotic fluid and placenta as controls
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Also, even if there is a flora in meconium, because its biomass is below the minimum that can be tested, it is difficult to distinguish whether it is pollution or bacteria that have been carried before birth (such as Bacteroides).
The blank control sample is used as a reference, but this does not completely rule out the possibility that this bacteria does not exist in meconium
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It is worthy of affirmation that the collection of meconium has advanced the time point of the detection of neonatal intestinal flora to an earlier stage, and can better explain the state of the intestinal tract of the prenatal infant
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The setting of numerous negative controls and blank controls also proves that when detecting samples with very low biomass, pollution from various sources has a decisive influence on the results and even conclusions of the experiment, which is quite instructive for similar research
.

In this view, it seems impossible to pass on the intestinal flora to the baby during pregnancy
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Facing the nearly sterile intestines of newborns, how to grasp the baby's birth and the short window period afterwards, so that probiotics can occupy the high ground first, is probably the next problem that scientists need to solve urgently
.

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01960130103007 Responsible editorBioTalker