Necrotizing enterocolitis (NEC) is a leading cause of morbidity and mortality among infants in the neonatal intensive care unit (NICU). It has been postulated that abnormal colonization of the preterm gut, or an unfavorable balance between gut bacteria may contribute to the development of NEC.

Recent clinical randomized studies and meta-analysis have shown that proactive colonization of probiotic bacteria reduce the frequency of NEC. Based on this evidence, in April 2014 all Norwegian NICUs started routinely administration of probiotics to all extremely premature neonates susceptible to NEC (gestational age <28 weeks/birth weight <1000g).

The current project is investigating the gut microbiome in patients receiving probiotics and compare the the gut microbiome with moderate premature infants not receiving probiotics. In addition, we are including a control of healthy full-term infants.

Samples containing feces from participants will be analyzed by state of the art whole-genome sequencing techniques. Bacterial diversity will be analysed with bioinformatic tools.

Study hypotheses:

• Probiotics given to extremely preterm infants will change the biodiversity of the gut microflora.
• Antibiotics given to these patients may influence the gut microflora also in infants receiving probiotics. In particular use of vancomycin may change the gut flora.
• After cessation of probiotic prophylaxis the gut flora of infants receiving probiotics will gradually resemble the gut flora of infants not receiving probiotics.
• A cross-contamination of probiotic bacteria between patients treated with probiotics and patients not treated with antibiotics may occur.

Necrotizing enterocolitis (NEC) is a leading cause of morbidity and mortality among infants in the neonatal intensive care unit (NICU). Prematurity is the most important risk factor for NEC. The pathogenesis of NEC remains unclear, and prevention and treatment strategies are limited. It has been postulated that abnormal colonization of the preterm gut, or an unfavorable balance between gut bacteria, is significant in the pathogenesis of NEC.

Recent clinical randomized studies and meta-analysis have shown that proactive colonization of probiotic bacteria reduce the frequency of NEC. Based on this evidence, in April 2014 all Norwegian NICUs started routinely administration of probiotics to all extremely premature neonates susceptible to NEC (gestational age (GA) <28 weeks/birth birth weight (BW) <1000 g).

The current project is investigating the gut microbiome in patients receiving probiotics and compare the the gut microbiome with moderate premature infants not receiving probiotics. In addition, we are including a control of healthy full-term infants.

Samples containing feces from participants will be analyzed by state of the art whole-genome sequencing techniques. Bacterial diversity and taxonomy will be analysed using bioinformatic tools

Inclusion criteria:

• Preterm infants 24-27 weeks gestation/ birth weight < 1000 g receiving probiotics
• Preterm infants 28-31 weeks gestation/BW 1000-1500 g not receiving probiotics
• Healthy term infants

Exclusion criteria

• Preterm infants < 24 weeks gestation
• Preterm infants < 32 weeks with severe lethal complication/poor prognosis around 1 week of age
• Infants with severe congenital malformations

Fecal samples will be obtained:

• 1 week of age
• 4 weeks of age
• 4 months corrected age
• 12 months corrected age

Study hypotheses:

• Probiotics given to extremely preterm infants will change the biodiversity of the gut microflora.
• Antibiotics given to these patients may influence the gut microflora also in infants receiving probiotics. In particular use of vancomycin may change the gut flora.
• After cessation of probiotic prophylaxis the gut flora of infants receiving probiotics will gradually resemble the gut flora of infants not receiving probiotics.
• A cross-contamination of probiotic bacteria between patients treated with probiotics and patients not treated with antibiotics may occur.

This is an explorative study. No formal sample size assessment is possible. Sequencing costs will be substantial. We will limit the number of participants to 26 x 2 preterm infants and 10 control healthy infants.

Six Norwegian Neonatal Intensive care units wil participate in the study.

Inclusion Criteria:

• Preterm infants with gestational age 24-27 weeks/birth weight < 1000 g, treated with probiotics (target number 26)
• Preterm infants with gestational age 29-31 weeks/birth weight 1000-1500 g, not treated with probiotics (target number 26)
• Term infants (target number 10)

Exclusion Criteria:

• Extremely preterm infants with gestational age below 24 weeks
• Preterm infants (24-31 weeks) with life threatening complications during 1 week of age
• Infants with congenital malformations

Preterm infants hospitalized in 6 Norwegian NICUs; divided in one group extremely preterm infants receiving probiotics and one group moderate preterm infants not receiving antibiotics. A group of helathy infants from the post-natal ward will also be included