The neonatal intestinal microbiota is a complex ecosystem composed of numerous genera, species and strains of bacteria. This enormous cell mass performs a variety of unique activities that affect both the colonic and systemic physiology. Its primary activities include nutritive, metabolic, immunological and protective functions. Most studies of infants have been based on faecal samples using the classical plating techniques with culturing on specific media. The limitations of these methods must be taken into account when evaluating the varying results of the different studies. The establishment of the gut microbial population is not strictly a succession in the ecological sense; it is rather a complex process influenced by microbial and host interactions and by external and internal factors. The climax intestinal flora is attained in successive stages. The foetal intestine is sterile and bathed in swallowed amniotic fluid. Following delivery, multiple different antigens challenge the intestine of the newborn. The maternal intestinal flora is a source of bacteria for the neonatal gut. The bacterial flora is usually heterogeneous during the first few days of life, independently of feeding habits. After the first week of life, a stable bacterial flora is usually established. In full‐term infants a diet of breast milk induces the development of a flora rich in Bifidobacterium spp. Other obligate anaerobes, such as Clostridium spp. and Bacteroides spp., are more rarely isolated and also enterobacteria and enterococci are relatively few. During the corresponding period, formula‐fed babies are often colonized by other anaerobes in addition to bifidobacteria and by facultatively anaerobic bacteria; the development of a “bifidus flora” is unusual. In other studies the presence of a consistent number of bifidobacteria in infants delivered in large urban hospitals has not been demonstrated, whether the babies were bottle fed or exclusively breastfed. The predominant faecal bacteria were coliforms and bacteroides. According to these studies, environmental factors may be more important than breastfeeding in gut colonization after delivery. Environmental factors are indeed extremely important for the intestinal colonization of infants born by caesarean section. In these infants, the establishment of a stable flora characterized by a low incidence of Bacteroides spp. and by the isolation of few other bacteria is consistently delayed. In extremely low‐birthweight infants, hospitalization in neonatal intensive care units, characterized by prolonged antibiotic therapy, parenteral nutrition, delayed oral feedings and intubation seems to affect the composition of the intestinal microbiota. The gut is colonized by a small number of bacterial species; Lactobacillus and Bifidobacteria spp. are seldom, if ever, identified. According to the few studies so far performed, the predominant species are Enterococcus faecalis, E. coli, Enterobacter cloacae, Klebsiella pneumoniae, Staphylococcus epidermidis and Staphylococcus haemolyticus. Hygie...

There was no difference in growth, crying, vomiting, and regurgitation patterns between the groups. In summary, acidic oligosaccharides from pectin hydrolysate are well tolerated as ingredient in infant formulae but do not affect intestinal microecology.

These data indicate that the addition of GOS (5 g/L) to a follow-on formula positively influences the bifidobacteria flora and the stool consistency in infants during the supplementation period at weaning. No local or systemic side effects were recorded.

The present review summarizes clinical and experimental data concerning the possible effects of a prebiotic mixture of short‐chain galacto‐oligosaccharides and long‐chain fructo‐oligosaccharides. The results from several studies, made up of over 400 preterm and term infants, clearly demonstrate that the prebiotic mixture under examination specifically stimulates the growth of bifidobacteria and lactobacilli and reduces the growth of pathogens. As a consequence of the changed intestinal flora by the dietary galacto‐oligosaccharides and fructo‐oligosaccharides, the faecal pH values and the short‐chain fatty acid pattern were similar to those found in breastfed infants. In addition, the stool consistency was the same as in breastfed infants. In vitro experiments have demonstrated that the specific short‐chain fatty acid pattern, at a pH similar to that found in faecal samples of breastfed infants, reduces the growth of pathogens in a dose‐dependent manner but does not influence the growth of bifidobacteria and lactobacilli. In an animal vaccination model, the prebiotic mixture improved the response to vaccination. In an allergy model (sensitization by ovalbumin), the allergic reaction was reduced by the prebiotic mixture. The data obtained from animal experiments are in agreement with preliminary data from clinical trials which indicate a reduced allergic response (reduced plasma IgE/IgG4 ratio) and reduced episodes of upper airway infection during the first year of life. Conclusion: Experimental evidence demonstrates that the prebiotic mixture employed in these studies modulates the intestinal flora and modulates the immune system as human milk does. There are sufficient experimental data to put forward the hypothesis that substances like the prebiotic mixture under study will substantially contribute to the improvement of the protective properties of infant formulas.

The development of the infant faecal flora was studied over the first three months of life in infants receiving breast milk, a modern adapted formula and adaptations of this formula. Breast-fed infants developed a flora rich in Bifidobacterium sp. Facultative anaerobes were ubiquitous, but in relatively small numbers within the diet group. Other obligate anaerobes, such as Clostridium sp. and Bacteriodes sp. were rarely isolated. Standard formula produced a flora rich in bifidobacteria, but the growth of facultative organisms was not suppressed by this diet. Clostridium sp. and Bacteroides sp. were more common in this feeding group. After the addition of lactoferrin at 10 mg/100 ml to the formula diet, a flora similar to that of the standard formula-fed babies was achieved. Lactoferrin at 100 mg/100 ml was able to establish a "bifidus flora" in half of the babies given this formula, but only at age three months. Clostridium sp. and Bacteroides sp. were common faecal isolates from babies receiving both the lactoferrin diets.