Binding of milk oligosaccharides by several enterotoxigenic Escherichia coli strains isolated from calves

Milk oligosaccharides have been proposed to play an important role in newborn defense, blocking bacterial adhesion to the intestinal mucosa and preventing infections. Some studies have been performed on human milk oligosaccharides. Here we checked whether bovine milk oligosaccharides would achieve the same protective action against the most common calf enteric pathogens. Seven enterotoxigenic Escherichia coli strains, isolated from diarrheic calves, were selected. All strains managed to agglutinate horse erythrocytes, and we therefore used the inhibition of hemagglutination in the presence of oligosaccharides as an indicator of the union between oligosaccharide and bacterial adhesins. Oligosaccharides from different stages of bovine lactation and standard oligosaccharides were assayed. Midlactation milk, in particular that corresponding to the transition period, proved to be the most efficient at inhibiting hemagglutination. The standard oligosaccharides used pointed to the preference of several strains (K99-, F41-, and F17-fimbriated) for alpha2,6-linked sialic acid. By contrast, B23 fimbriae exhibited higher affinity for alpha2,3-sialylated isomers and B64 seemed to require N-acetylglucosamine for binding. Our results suggest a general trend for milk oligosaccharides. Probably they participate in the protection of newborn mammals from pathogens.