Aim: Gut dysbiosis is associated with acute and long-term health problems. Probiotics are widely used to prevent dysbiosis in extremely preterm infants. Yet, the evidence from studies is inconclusive and focused on short term effects. We aim to define the potential of probiotics for modulating both the intestinal microbiome and the developing immune system in preterm infants.

Design: The multi-center, double-blind, placebo-controlled PRIMAL Clinical Study aims to determine, whether Bifidobacterium/Lactobacillus acidophilus probiotics reduce the risk for gut dysbiosis in preterm infants (gestational age between 28+0 and 32+6 weeks) at 28 days and 12 months of life. This vulnerable population is frequently exposed to putative disturbances of host-microbiome interaction and observed under controlled conditions. Microbiome composition will be assessed by high-resolution microbiome analysis. Several aspects of antimicrobial immunity will be studied in blood samples obtained in the neonatal period and at 12 months of life.

Expected outcome: We expect probiotics to ameliorate gut dysbiosis, in particular in infants exposed to antibiotics, where the risk is particularly high. This trial is designed to derive profound new evidence, to clarify efficacy and mechanisms of probiotics in preventing long-term health problems of preterm infants, i.e. infections and growth failure.