Chemistry Reference
In-Depth Information
ATCC 15697 and it was found that tri- to hepta-saccharides were completely
degraded during the growth over 25 and 50 h (LoCascio et al., 2007).
Intestinal colonization by bifidobacteria is especially important to the
health of infants because there is evidence that it prevents infection by some
pathogenic organisms and reduces the incidence of diarrhea (Bezkorovainy,
1989). In breast-fed infants, bifidobacteria usually dominate the intestinal
flora within 1 week after birth, constituting 95-99.9% of the bacterial popula-
tion over time (Rotimi and Duerden, 1981; Benno and Mitsuoka, 1986). By
contrast, intestinal colonization by bifidobacteria is not as rapid or as pre-
dominant in bottle-fed infants, who, prior to the early 20th Century, often
experienced infection by pathogenic bacteria (Bezkorovainy, 1989). To
improve the growth of intestinal bifidobacteria, saccharides such as lactulose
(Petuely, 1957) have been used as supplements to formula milk, resulting in
bottle-fed infants being healthier. However, the intestinal flora of bottle-fed
infants consists of about 90% bifidobacteria and 10% Enterobacteriaceae;
this ratio is smaller than that in breast-fed infants (Benno et al., 1984).
Growth factors for bifidobacteria in human milk, so-called bifidus
factors, have been investigated for many years. It was initially thought that,
in this regard, nitrogen-containing sugars represented the main difference
between breast milk and formula, but this was shown to be due to the use of a
strain of Bifidobacterium bifidum that requires GlcNAc for growth (Gyorgy
et al., 1954; Veerkamp, 1969). Further studies revealed that oligosaccharides
in human milk are candidate bifidus factors (Bezkorovainy, 1989), but a
specific oligosaccharide responsible for stimulating the growth of bifidobac-
teria was not identified, mainly because of the complexity caused by the fact
that human milk contains more than 100 kinds of oligosaccharides. Recently,
however, Kitaoka et al. (2005) presented a new hypothesis based on a novel
metabolic pathway for galactose in bifidobacteria, which proposed that
Gal(
1-3)GlcNAc (lacto-N-biose I, LNB) structures, which are found in
type I human milk oligosaccharides, act as specific bifidus factors.
Derensy-Dron et al. (1999) reported the presence of an enzyme in cell-free
extracts of B. bifidum that reversibly converted LNB to
-
D
-galactopyranose-
1-phosphate (Gal-1-P) and GlcNAc. This enzyme, which also converts Gal(
1-
3)GalNAc (galacto-N-biose, GNB) to Gal-1-P and GalNAc, was named
-1,3-
galactosyl-N-acetylhexosamine phosphorylase (EC 2.4.1.211) (Derensy-Dron
et al., 1999). Subsequently, a shorter name, lacto-N-biose phosphorylase
(LNBP), was used for this enzyme (Kitaoka et al., 2005). Derensy-Dron et al.
(1999) assumed that the enzyme played a role in the metabolism of mucin
sugars by bifidobacteria during colonization of the intestine. This assumption
has been supported by the presence of a bifidobacterial endo-
-N-acetylgalac-
tosaminidase that hydrolyzes the linkage between galacto-N-bioside and serine
or threonine in O-linked glycoproteins of mucins (Fujita et al., 2005).
