Bacteria produce carbohydrate-specific adhesins which are frequently located on their fimbriae or pili. Prominent examples for colonization via Sia are pathogenic bacteria such as strains ofE. coli, Streptococci and Helicobacter pylori. Especially the latter
bacterium, often found in the human stomach and responsible for gastric inflammation and possibly cancer, is intensively studied. Mahdavi et al. (2002) published the structure of its Sia-recognizing adhesin. Knowledge about such adhesion mechanisms enables a
biology-based therapy of diseases and reduces the use of antibiotics (Gerhard et al., 2001). Thus, receptor–ligand interactions may be inhibited with soluble ligands such
as sialylated oligosaccharides or glycoproteins. Such oligosaccharides occur in a relatively high concentration in milk, especially in the colostrum. The milk from each
mammalian species contains different and more or less sialylated glycans (Urashima et al., 2001). These carbohydrates are considered to regulate the speciesspecific colonization of the intestine with microorganisms and to prevent the attachment of pathogenic bacteria such as E. coliand Helicobacterstrains or pathogenic viruses, e.g. rota viruses, which is especially important in newborns. It should be noted that a high
Sia content in breast milk, especially during the first days after birth, was shown to increase the Sia content of brain gangliosides in rats and man and is discussed to
promote permanently higher intelligence (Wang and Brand-Miller, 2003). Bacterial toxins, such as cholera, tetanus and diphtheria toxin, firmly adhere to Sia, mostly those situated on gangliosides, as basis of their pathophysiological activity (summarized inKelm and Schauer, 1997).