The presence of different microbiota in human adults depending on the parts of the body (intestine, skin, mouth,…), has been widely studied in recent years and is now well recognized. However, there are still many questions about colonisation at the beginning of life and how this is a determining factor for our future health. For many years, the unborn child was considered sterile. Today, microbial research is challenging this paradigm by suggesting that the newborn is not born sterile.
In 2017, Chu et al studied variations in the neonatal microbiota at delivery and then at 6 weeks of age on several body sites (skin, oral cavity, nostrils and feces) among a cohort of 157 pregnant women. At delivery, the results of the study demonstrated that the structure of the neonatal microbial community remains homogeneous whatever the body sites studied (mouth, nostrils, skin), with the exception of the digestive microbiota. Indeed, while the analysis of the different sites taken from the child revealed a microbiota similar to the mother’s vaginal or cutaneous microbiota (depending on the mode of delivery by vaginal or caesarean section, respectively), the analysis of meconium (first stool of the newborn) showed that the digestive microbiota has a maternal origin distinct from that of the other microbiota of the newborn.
Surprisingly, the digestive microbiota of the newborn is home to 10% of bacteria belonging to the genera Escherichia and Klebsiella. These bacteria are opportunistic commensals, i.e., bacteria normally present in the body without affecting it, but which can cause illness as a result of a decrease in the body’s defences. What is the origin of these bacteria?
Surprisingly, the digestive microbiota of the newborn is home to 10% of bacteria belonging to the genera Escherichia and Klebsiella. These bacteria are opportunistic commensals, i.e., bacteria normally present in the body without affecting it, but which can cause illness as a result of a decrease in the body’s defences. What is the origin of these bacteria?
A recent study questioned the model proposed by Chu and his team. In 2019, MC de Goffau et al. published a study proving the absence of the placental microbiota.
Through the study of placental biopsies from 537 women, the amount of bacterial DNA found in the placenta is very low and could be the result of contamination:
- Contamination of the placenta during labor or delivery…
- Contamination of the placental sample during the pre-analytical (sampling) and analytical (DNA extraction) stages
- Contamination related to the reagents used
In this study only one signal was qualified as authentic, the presence of Streptococcus Agalactiae (Group B Streptococci). This signal was detected in about 5% of the samples taken before the beginning of the work and was validated by 2 independent methods (16S metagenomics and qPCR). Among all the signals observed, this is the only organism found that met all the criteria for a true bacterial signal associated with the placenta and not with contamination. Thus, in their study, the authors conclude that the human placenta does not possess a microbiota, but that it represents a potential source of Streptococcus Agalactiae infection, which is known to be a major cause of neonatal sepsis.
In this study only one signal was qualified as authentic, the presence of Streptococcus Agalactiae (Group B Streptococci). This signal was detected in about 5% of the samples taken before the beginning of the work and was validated by 2 independent methods (16S metagenomics and qPCR). Among all the signals observed, this is the only organism found that met all the criteria for a true bacterial signal associated with the placenta and not with contamination. Thus, in their study, the authors conclude that the human placenta does not possess a microbiota, but that it represents a potential source of Streptococcus Agalactiae infection, which is known to be a major cause of neonatal sepsis.
M. Ibarlucea & A. Plauzolles
References
– Chu, D. M., Ma, J., Prince, A. L., Antony, K. M., Seferovic, M. D., & Aagaard, K. M. (2017). Maturation of the infant microbiome community structure and function across multiple body sites and in relation to mode of delivery. Nature medicine, 23(3), 314.
– de Goffau, M. C., Lager, S., Sovio, U., Gaccioli, F., Cook, E., Peacock, S. J., … & Smith, G. C. (2019). Human placenta has no microbiome but can contain potential pathogens. Nature, 572(7769), 329-334.