In this week’s writing exercise, I am asked to reflect on potential factors/circumstances of childbirth and rearing that might modulate the transfer of microbial communities from mother to child.

As we discussed in class, human beings are entirely sterile before exiting from the womb, or “birth” as we more commonly refer to it as. Any microbiologist knows, however, that this state does not last for long and is a relative blip in the lifespan of the human. Perinatally and onwards, humans are exposed to bacteria, which naturally comes with being colonized by certain bacterial species. This is meant to happen and is mechanically facilitated during birth. The close proximity of the anus to the birthing canal promotes the colonization of the neonate with the mother’s bacteria; in this way, vaginal birth has a positive effect on the diversity of the baby’s microbiome. Not all babies are born vaginally, however, as some are born Cesarian, sometimes by necessity. As a Cesarian is a highly invasive surgical procedure, a sterile field is ensured by all of the surgeons, meaning the baby does not see the same level of exposure to the bacteria as it would if it was born vaginally. Being delivered via the Cesarian method has a negative impact on the neonate’s microbial diversity.

In terms of the months following the delivery of the baby, the baby’s diet is liquid, either being the mother’s milk (chest-feeding) or through formula. In class, we talked about how antibodies are passed from mother to child via the milk, which modulates the baby’s microbiome. This modulation actually has a positive effect on the baby’s microbial diversity, as these antibodies weaken bacterial populations that are in dysbiosis. Conversely, babies fed formula do not ingest these antibodies and therefore do not see the same modulation of their microbiomes. Compared to a baby that is chest-fed, we would consider being fed formula as having a negative impact on the baby’s microbial diversity.