Chemistry Reference
In-Depth Information
specific adaptation to this highly competitive ecological niche, especially in breast-
fed infants.
53
All these data provide strong evidence that many HMOS are preferentially syn-
thesized to be metabolized as prebiotic ingredients by intestinal microbiota rather
than to be used as a nutritional substrate.
Apart from their prebiotic effects, there is also evidence that HMOS act as recep-
tor analogues to inhibit the adhesion of several pathogens on the epithelial surface.
54
There are many different target structures of pathogens,
43
which might partially
explain the great variety of structures of HMOS. On the other hand, the protection
against adhesion of pathogens might open opportunities for interactions of commen-
sal bacteria with the epithelial surface that seems to be of physiological importance.
15.2.3 other Functions of hMos
As carbohydrate compounds are a main part of structures on the cellular sur-
face, HMOS can act as signaling molecules that might explain the great variety of
functions attributed to HMOS.
38-43
The possibility that HMOS interact directly with
immune cells is of particular interest. Such direct interactions have been reported
with selectins,
55
dentritic cell-specific C-type lectin,
56
integrins,
57
and other target
receptors.
58
In an
in vitro
study, particularly acidic HMOS demonstrated a direct
effect on the number of activated or regulatory T cells.
59
Because HMOS are resistant to digestion and the maturation of the gut is not
fully developed,
60
they can pass the intestinal wall in smaller amounts (approxi-
mately 1 percent of intake).
46
It can be speculated that the appearance in the plasma
and the distribution across the whole body might be one factor for a possibly direct
systemic effect of HMOS on the immune system. However, this hypothesis needs
further investigation.
15.2.4 human Milk and breastfeeding as the source of bacteria
For many years studies on the microbiology of breast milk have been restricted
to transmission of pathogenic bacteria. This was mainly in relation to mastitis and
contamination of breast milk related to its use in milk banks. Only a few studies
are available in which bacteria from breast milk samples of healthy women were
analyzed. These studies show that low amounts of bacteria are present in human
breast milk. This may, however, be due to contamination or may originate from the
ducts or areola of the breast. Bacterial strains isolated from breast milk included
lactobacilli,
Streptococcus, Enterococcus, Peptostreptococcus, Staphylococcus,
and
Corynebacterium,
with sometimes
Escherichia
spp.
61- 63
Recently, the presence of
bifidobacteria has also been shown.
64,65
Bacterial numbers detected in breast milk
range from lower than 1 × 10
3
to a maximum of 1 × 10
5
colony-forming units (cfu)/
mL. Differences in bacterial numbers may be due to contamination and organisms
residing in the ducts or on the areola of the breast.
61- 63
Bacterial studies in breast
milk, therefore, need to be repeated and their biological significance needs to be
elucidated. It has been shown that transfer of bacteria through breastfeeding is one
