Microbiome and immune development in preterm infants receiving powdered human milk‐based fortification from the PUFFIN trial

OBJECTIVE: To determine the impact of powdered human milk-based fortification (PHMF) compared to powdered bovine milk-based fortification on gut microbiome and inflammation in preterm infants. METHODS: Mechanistic study within randomised controlled trial in infants <32 weeks gestation or <1500 g birthweight, only receiving human milk and fully enterally fed without previous fortification, in two UK neonatal intensive care units (NICU). Stool and urine at recruitment (D0), weekly until day 21 (D21) and discharge. Microbiota (stool) and secretory immunoglobulin A (sIgA)/IgA (stool and urine) were evaluated at all time points and immune related proteins (IRP) (stool) at day 7 (D7) and D21. RESULTS: Twenty-eight patients (14 per arm; median gestation 27.18 ± 2.42 weeks) participated. One hundred and twenty-nine stools and 109 urines were collected. Analysis of gut microbiota (111 stools), sIgA (113 stools and 108 urines), and IRPs (52 stools) was performed. Fortifier type did not significantly impact stool alpha or beta diversity or specific taxa and explained <5% of variance at any time point, with site being most influential (14.7% at day 14 [D14], p = 0.04; 25.7% at D21, p = 0.007). Stool but not urine sIgA was higher in PHMF recipients. Whilst fortifier type was not associated with IRPs from D7 to D21, NICU site impacted IRPs. CONCLUSIONS: Fortifier type did not have a large impact on microbiota or IRPs but stool sIgA was higher in PHMF recipients. An association between NICU site and other outcomes was observed. TRIAL REGISTRATION: ClinicalTrials.gov identifier: The Preterm milk fortification in neonates (PUFFIN) study was prospectively registered ISRCTN 22484792.