Oral probiotics in preterm infants and bacterial signatures in consecutive stool samples

Introduction: In preterm infants the risk of Necrotizing Enterocolitis (NEC) is reduced by oral probiotics. The protective effect could be associated with changes of the gut flora (direct effects) or by indirect effects modulating bacterial-host-interaction at the mucosal interface or the intestinal or systemic immune system. Material and Methods: In the present prospective randomized cross-over study we analysed the development of the bacterial community in stool samples of preterm infants for the first 6 weeks of life. 21 preterm infants at a gestational age <32 weeks and with birth-weight <1500g were included. Groups supplemented with Lactobacillus acidophilum and Bifidobacterium infantis (Infloran®) in week 1–3 (group 1) and in week 4–6 (group 2) were compared. The signatures of multiple bacterial genomes were regularly monitored in stool samples by Denaturing Gradient Gel Electrophoresis (PCR-DGGE) and the specific bands were identified by subsequent sequence typing. Bacterial signatures are actually available of >300 samples (10 patients). Results: Bacterial DNA could not be amplified in the first stool sample (meconium), except for few patients with congenital infections. In the first weeks of life the development of an individual bacterial pattern was monitored in stool samples. We could show that the development and the composition of the predominant bacterial species in infants stool were not altered by modulation of probiotic supplementation. In both groups, the development of infants stool flora was initiated by colonisation with gram-negative bacteria, followed by gram-positive cocci and finally anaerobic bacteria. However, antibiotic interventions were associated with changes of bacterial signatures. Interestingly, specific bands for L. acidophilum and B. infantis were almost not detected despite probiotic substitution. Conclusions: Despite the limitations due to the few cases it may be concluded that probiotic supplementation was not associated with significant changes of preterm infants stool flora. Therefore we hypothesize that prevention of NEC might be associated with more indirect effects which remains still to be confirmed in future studies.