Aim To describe intestinal microbiota in preterm infants admitted to the Neonatal Unit using molecular techniques, and assess the impact of different conditions.

Methods/study design A two year period Descriptive study (2011–2012) of gut microbiota in stools from newborns borns under 35 week gestational age (WGA) at birth, admitted in a Neonatal Care Unit. Stool samples were collected: M1 (meconium), M2 (first week), M3 (first month). 5 groups of bacteria were analysed using qPCR technique: Bacteroides, Bifidobacterium, Escherichia coli, Clostridiums and Lactobacillus. Maternal, perinatal and neonate variables were registered. Statistic programs SPSSvs 20.

ResultsIn the first month a marked increase (x120) in Bifidobacterium is observed. The increase of Lactobacillus (x2) and E. coli (x7) is lower. Bacteroides and Clostridium remain stable.

Regarding WGA in ≤ 30 vs > 30 we observed:

- Bifidobacterial colonisation is delayed at birth (2,35 × 10⁴ vs 6,02 × 10⁴ cfu/g; p = 0,09) and at one week birth age (3,98 × 10⁴ vs 1,49 × 10⁶ cfu/g; p = 0,007).

- Higher numbers of E. coli from the first sample (4,37 × 10³ vs 9,07 × 10² cfu/g; 1,55 × 10⁴ vs 2,93 × 10³ cfu/g; 2,94 × 10⁴ vs 9,69 × 10³ cfu/g), although no significant statistically differences were detected.

Conclusions The number of Bifidobacterium and Lactobacillus in faecal samples is higher than the content in Bacteroides, Clostridium and E.coli. The colonisation process of studied bacteria is delayed in prematures born at lower WGA, except for E. coli.