Neonatal gut microbiome and immunity

Abstract

Early life is a critical time window for the neonatal gut to be progressively populated with different bacterial species that collectively promote gut maturation. A fully developed and healthy gut microbiome in neonates is an important driver for the development of other aspects of health. Unlike the relatively stable gut microbiome in adults, the developing gut microbiome in neonates exhibits higher plasticity and adaptability. This also underscores the unique window of opportunity for intervention or preventive measures to improve long-term health through modulations of the gut microbiome in early life. Better understanding of the neonatal gut microbiome - how it arises and how it impacts immune cell development - will help us appreciate the underpinnings of immune-related diseases. Here, we examine recent findings on the neonatal gut microbiome and discuss their implications for understanding this important driver of the maturation of the immune system and immunity against infections in early life.

Figure 1.. The changing gut lumen environment from early life to adulthood affects the relative abundance of bacteria.

The gut lumen of newborns begins with a high abundance of oxygen which allows for the colonization of facultative anaerobes Enterobacteriaceae and Lactobacillaceae right after birth. Bifidobacteriaceae begin to increase due to the simple sugars and human milk oligosaccharides (HMOs) in the gut lumen from consumption of maternal breast milk. Simultaneously, Clostridiaceae abundance starts increasing which leads to the production of SCFAs like butyrate to induce oxygen metabolism by the intestinal epithelium. This hypoxic gut environment, in addition to the cessation of breast-feeding and switch to solid foods consisting of complex carbohydrates, allows for the colonization of obligate anaerobes Bacteroidaceae, Porphyromondaceae, Lachnospiraceae, and Ruminococcacea which become the most abundant bacteria as adults.