Importance of the Gut Microbiome in Preterm Infants.

Birth represents the start of an incredible journey for the individual and the microbes which reside within and upon them. This interaction between human and microbe is essential for healthy development. Term infants are colonized by bacteria at birth, and thereafter the diet is the most important factor shaping the gut microbiome, in particular receipt of human milk. Human milk contains viable bacteria and numerous components that modulate the bacterial community, including human milk oligosaccharides (HMOs) which promote the growth of Bifidobacteriumspecies. Notably, Bifidobacteriumspp. are the primary bacterium used in probiotic supplements, owing to their association with positive outcomes in cohort studies and range of beneficial properties in mechanistic experiments. Preterm infants born <32 weeks' gestation encounter an unnatural beginning to life, with housing in "sterile" incubators, higher rates of caesarean delivery and antibiotic use, and complex nutritional provision. This reduces Bifidobacteriumabundance and overall microbial diversity. However, this also presents an opportunity to use probiotics and prebiotics (e.g., HMOs) to restore "normal" development. Much work has focused in this area over the past two decades and, while more work is needed, there is promise in symbiotic intervention to modulate the microbiome and reduce disease in preterm infants.