Our data confirm lower lactose concentrations in preterm milk, compared with term milk, and they provide the first detailed characterization of oligosaccharides in preterm milk, demonstrating important differences in oligosaccharide contents in the 4 groups. These differences might exert an influence on several biological functions that are particularly important for preterm infants and currently are attributed to milk oligosaccharides.

Breast-fed children, compared with the bottle-fed ones, have a lower incidence of acute gastroenteritis due to the presence of several antiinfective factors in human milk. The aim of this work is to study the ability of human milk oligosaccharides to prevent infections related to some common pathogenic bacteria. Oligosaccharides of human milk were fractionated by gel-filtration and characterized by thin-layer chromatography and highperformance anion exchange chromatography. Fractions obtained contained, respectively, 1) acidic oligosaccharides, 2) neutral highmolecular-weight oligosaccharides, and 3) neutral low-molecularweight oligosaccharides. Experiments were carried out to study the ability of oligosaccharides in inhibiting the adhesion of three intestinal microorganisms (enteropathogenic Escherichia coli serotype O119, Vibrio cholerae, and Salmonella fyris) to differentiated Caco-2 cells. The study showed that the acidic fraction had an antiadhesive effect on the all three pathogenic strains studied (with different degrees of inhibition). The neutral high-molecular-weight fraction significantly inhibited the adhesion of E. coli O119 and V. cholerae, but not that of S. fyris; the neutral low-molecular-weight fraction was effective toward E. coli O119 and S. fyris but not V. cholerae. Our results demonstrate that human milk oligosaccharides inhibit the adhesion to epithelial cells not only of common pathogens like E. coli but also for the first time of other aggressive bacteria as V. cholerae and S. fyris. Consequently, oligosaccharides are one of the important defensive factors contained in human milk against acute diarrheal infections of breast-fed infants. (Pediatr Res 59: 377-382, 2006) I nfectious diarrheal diseases constitute a leading cause of infant morbidity not only in developing countries but also in developed areas (1). In fact, in the United States, acute diarrhea represents an important cause of childhood morbidity, especially during the first years of life, determining an economical loss that has been estimated in the order of several millions of dollars (2).In infants, infections of the gastrointestinal tract are caused by a wide variety of enteropathogens, including bacteria, viruses, and parasites. There is now strong evidence supporting a relationship between breast-feeding and a lower incidence in diarrhea. Breast-feeding offers protection with different mechanisms against diarrhea due to several antiinfective substances present in human milk, such as secretory antibodies, lactoferrin, lysozyme, etc. (3-5).In the last 15 y, evidence has also emerged on the protective role of another group of substances, oligosaccharides (6 -8). They are synthesized in a large number by specific glycosyltransferases present in the mammary gland through the sequential addition to lactose of fucose, galactose, Nacetylglucosamine, and sialic acid. Each single oligosaccharide varies dynamically during the different phases of lactation (9). From the quantitative point of view, oligosaccharides, all tog...

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Our data show that milk groups 1, 2, and 3, containing an amount of oligosaccharides ranging within 10 to 15 g/L, share a substantially identical composition of the intestinal microbiota in breast-fed infants, despite quali-quantitative difference in oligosaccharides content. Newborns taking milk with only 5 g/L of oligosaccharides (group 4) harbour a different intestinal microbiota.

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