The maternal influence on the establishment of the fetal microbiota
Not all maternal-fetal interactions are known, particularly microbial interactions in such a protected environment as the placenta. A Finnish team has investigated the maternal influence on the fetal microbiota, whose immunological benefit is yet to be determined.
The human placenta has recently been associated with the presence of immunologically beneficial bacteria such as Lactobacilli and Bifidobacteria. However, the influence and effects of intrauterine exposure to bacteria remain obscure. As invasive techniques cannot be performed on pregnant women, the researchers studied the meconium of newborns, which is thought to reflect the fetal microbiome, in order to evaluate the impact of influential intrapartum maternal factors and that of immediate perinatal factors on the microbiota of the meconium.
The bacterial diversity of the meconium
Analysis of meconium samples demonstrated the existence of a specific bacterial diversity. Firmicutes were the most abundant phylum (relative abundance of 44%), followed by Proteobacteria, (28%) and Bacteroides (15%). Ahead of Bacteroides and Streptococci, Staphylococci were the most abundant genus (relative abundance of 15%), particularly in children born vaginally, probably reflecting the first effects of peripartum skin contact.
Influence of the maternal environment
Multivariate analysis showed that the biodiversity of the environment inhabited by the mother (the selected indicator was the number of pet animals at home) increased microbial diversity in the fetus. This diversity occurred at the expense of bacteria from the Bacteroides and Faecalibacterium genera. Consumption of Lactobacillus probiotics during pregnancy was thought to produce a slight increase in the abundance of the Lactobacillus genus. These results therefore suggest a transfer in utero of bacteria from the mother to the unborn child.
The direct environment of the newborn has no effect
Like the mode of delivery, gestational age, or exposure to antibiotics during labor, perinatal factors surprisingly had no effect on the microbial diversity of the meconium. On the other hand, consumption of antibiotics by the mother during pregnancy made the search for bacterial DNA in the meconium more difficult. Although the mechanism of bacterial colonization in utero is still poorly understood, it appears that the process is impaired by the administration of antibiotics to the mother. This medication influences colonization of the fetal intestines and intrauterine bacterial transfer. The immunological effects of the fetal microbiota should be a source of future studies, especially as bacterial exposure in utero can be investigated using non-invasive methods.
Terhi Tapiainen, Niko Paalanne, Mysore V Tejesvi, Pirjo Riikola M, Katja Korpela, Tytti Pokka, Jarmo Salo, Tuula Kaukola, Anna Maria Pirttila ̈, Matti Uhari, Marjo Renko. Maternal influence on the fetal microbiome in a population-based study of the first-pass meconium. Pediatric Research accepted article preview 14 March 2018; doi: 10.1038/pr.2018.29