The administration of antibiotics to infants has the capacity to profoundly affect the early acquisition, establishment, and natural maturation of commensal microflora. Prematurity is another major factor that is thought to influence 'normal' gut microbial composition in early life. A high number of pre-term infants receive antibiotic therapy prophylactically; the immediate and long-term effects of antibiotic treatment on infant and later health outcomes are unknown. We hypothesize that gestational age influences the ability to support 'normal' gut microbiota, and that antibiotic administration in the first few weeks of life can alter or delay the development of a 'normal' microbiota and may lead to adverse health outcomes. If we hope to promote the healthy establishment of early gut colonization and thereby improve health outcomes, we need to establish what 'normal' colonization looks like across gestational ages and apply this knowledge as a benchmark to understand the impact of antibiotic treatment in early postnatal life.

In this project, we propose to examine the microbiome in four cohorts ranging from extremely preterm to term, with birth weights appropriate for gestational age: Group 1) 23 to 27 weeks and extremely low birth weight [ELBW, <1000 grams]; Group 2) 28 to 32 weeks and very low birth weight [VLBW, >1000 to <1500 grams]; Group 3) 33 to 36 weeks and low birth weight [LBW, >1500 to <2500 grams]; and Group 4) term (37 to 42 weeks) and normal [>2500 to <4000 gram] birth weight. The infant gut microbiome will be assessed longitudinally in study infants from the first postnatal week to 18 months of age, and will include untreated and antibiotic-treated infants.

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