The maternal microbiome: another bridge linking mothers and infants

Abstract

A total of 10 100 trillion microbes live symbiotically within each human host and are thought to affect our physical and mental health. The health effects are thought to begin as early as the gestational period. Research shows that maternal gut microbes may have both direct and indirect effects during pregnancy. For example, a dysregulated gut microbiome is thought to promote intestinal inflammation, which in turn could lead to a shortening of the gestational period and a reduction in birthweight. The gut microbiome can also influence nutrient absorption during pregnancy and cause more global effects on gestation and fetal growth. Some adverse pregnancy outcomes, such as preterm birth and low birthweight, are more prevalent in low-income and middle-income countries (LMIC). Despite the important role of maternal gut microbes on these outcomes, most studies to date have been done in highincome populations. This misalignment urges more studies on maternal gut microbiome in LMICs. Recently in June issue of EBioMedicine, Ethan Gough and colleagues reported the relationship between the maternal faecal microbiome and gestational age, birthweight, and neonatal growth in rural Zimbabwe. They found that Blastoscystis sp, Brachyspira sp, and Treponeme carriage were higher in this Zimbabwe cohort than populations in high-income countries. Resistant starch-degraders were the predominant finding and were important predictors of birth outcomes. Zimbabwean mothers included in this study consumed diets that were high in maize. It’s thought that the resistant starch-degraders could help to release energy from polysaccharides in the maize that cannot be digested by host enzymes and therefore provide an important nutrient-harvesting function for these mothers. The study also investigated the metabolic pathways and enzymes present in the maternal gut microbiome and found that pathways related to environmental sensing, vitamin B metabolism, and signalling were associated with increased infant birthweight and better neonatal growth, while those related to functions involved in biofilm formation in response to nutrient starvation predicted reduced birthweight and worse growth. In addition to influencing neonatal growth, evidence indicates that the maternal gut microbiome also affects infant psychological development. As early as 2016 in Cell, Shelly Buffington and colleagues showed that a high-fat diet induced a shift in maternal gut microbiota in a mouse model, especially the lowered abundance of Lactobacillus reuteri, which reduced oxytocin levels in the hypothalamus of the offspring and negatively affected their social behaviour. Supporting this animal study, in the June issue of EBioMedicine, Samantha Dawson and colleagues found that taxa from butyrate-producing families Lachnospiraceae and Ruminococcaceaewere more abundant in mothers of children with normative behaviour. A healthy prenatal diet, including a high intake of fish, nuts, eggs, green vegetables, whole grains, and a low intake of white bread, sugar, full-cream milk, and hamburgers, indirectly related to decreased internalising behaviour in children via higher alpha diversity of maternal faecal microbiota. Although further studies are needed