Aims Despite the effect of enteral feeding on the development of intestinal microbiota in preterm infants remaining poorly understood, trials aiming to prevent necrotising enterocolitis (NEC) using probiotics are well-established. Exclusively breast milk fed preterm infants have a reduced risk of developing NEC and this may be linked with a more ‘beneficial’ gut microbiota.

Methods The NAPI Study (see abstract BEAT82431) sequentially recruited infants <32 weeks and <1.5Kg birth weight. Non-meconium faecal samples from the first and fourth weeks of life in 22 infants, 12 with NEC, were analysed by PCR-Transient Temperature Gel Electrophoresis using universal bacterial primers. Species richness and similarities were compared between infants according to feed type: EBM, expressed breast milk, vs Mixed, breast and formula milks.

Results There was large variability between number (1–17) and species diversity (25–36 different species). Number of predominant bacterial species did not increase between the 1st and 4th week of life. Bacterial composition varied largely between the 2 sample points, No difference in species richness or similarity within the 2 feeding groups was observed. 4 bands were identified in >50% of infants. Intra-individual similarity varied greatly and ranged from a similarity index (Cs) of 0% to 66.8%. There was no statistical difference between the similarity indices of the feeding groups (p = 0.8852) or between those with and without NEC (p = 0.1719).

Conclusion Microbial community of preterm neonates undergoes several interindividual changes during their first month of life. The feeding mode did not seem to have a major impact on the development of bacterial diversity.