Maternal microbiota in pregnancy and early life.
McDonald B, McCoy KD
Science. Sep 2019. doi: 10.1126/science.aay0618
COMMENT: In this work the authors analyze the most important findings done during last years about maternal and newborn microbiota reviewing its involvement in the susceptibility to some illnesses.
It is clear that a connection between newborn microbiota and maternal microbiota exists. Thus, newborn’s skin and mucosal surfaces are seeded with microorganisms from the mother and, hence, the first microbes encountered in early life come from the maternal microbiome.
Whether intrauterine environment is sterile or not is now controversial. Bacterial DNA has been found in placental and chorioamniotic tissues and culturable microbes have been isolated from newborn meconium.
Some differences in the microbiome taxonomic profile have been detected between newborns delivered by caesarian section and those vaginally delivered and there are some evidences suggesting the association of caesarian section with increased risk of adverse childhood health outcomes. Observational studies of maternal–infant pairs show that after 6 weeks the differences in the microbiome of cesarean and vaginally delivered newborns is minimal.
Links between the composition of the maternal microbiome and subsequent risk of childhood illnesses, including infection, asthma, allergy, autoimmunity, and metabolic diseases such as obesity and diabetes have been reported. It is important to study how these microbiome-associated phenotypes can be vertically transmitted from mother to child. One possibility is via maternal microbiota seeding during vaginal delivery and another possible manner to be transmitted could be via breastfeeding. Some works support that this transmission could impact not only the infancy period but also the adulthood.
Immune system development is another critical point related to the microbial colonization during early life:
…colonization by microbes in early life is critical for normal immune development, including immune cell production (comprising myeloid and lymphoid lineages), development of lymph nodes, antibody production, T cell polarization, and immune regulatory functions, as well as innate immunity and epithelial barrier integrity.
Breastfeeding is a key mechanism to transmit maternal microbes to the newborn at the same time that to supply nutrients and antimicrobial factors. All these elements can shape the infant’s gut microbiome.
Neuroimmune development is also controlled by microbiome and there are sufficient evidences that support the existence of a microbiota-mediated gut–brain axis. This axis is related to the susceptibility to neurodevelopmental disorders as autism and psychiatric illnesses that have been associated to microbiome dysbiosis.
Finally we include here a conclusion of the author that summarizes the state of the current knowledge about maternal and newborn microbiome and how to apply this knowledge for early prevention and treatment of diseases:
Although much has been learned about the maternal microbiota in pregnancy and early life, many fundamental questions remain. It is unclear if this information can be used to prevent and treat childhood illnesses. To do so, are live microbial therapeutics needed, or will specific bacterial products or metabolites suffice (and if so, which ones)?