Pediatric Nutrition in Practice

Gut Microbiota in Infants 89

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through the first years of life (summarized in fig. 1 ).
Weaning is associated with changes including in-
creased levels of Escherichia coli , enterococci, bac-
teroides and anaerobic gram-positive cocci and de-
creased enterobacteria. Differences between breast-
fed and formula-fed infants seem to disappear.
By 1–2 years of age, the microbiota resembles
that of adults, although levels of bifidobacteria
and enterobacteria in children (16 months to 7
years) remain higher t han in adu lts. Early change
of the microbiota to the adult type may be linked
with development of eczema [9]. The intestinal
microbiota is crucial for normal development of
the gut-associated lymphoid tissue and has im-
portant effects on intestinal mucosal barrier
function and other aspects of intestinal function.

I m m u n e D e v e l o p m e n t

Microbial colonization of the newborn intestine
is required for normal immune development,
which in turn is important for regulation of gut

inflammatory responses and oral tolerance in-

duction. The mucosal immune system of the gas-

trointestinal tract is constantly challenged by di-

verse antigens, such as microbial and food anti-

gens. Such priming of the gut-associated lymphoid

tissue is important for two opposing functions:

mounting a response to pathogens and maintain-

ing hyporesponsiveness to innocuous antigens.

Mice raised in a germ-free environment fail to de-

velop oral tolerance and have a persistent Th2-

dependent antibody response [11]. This immune

deviation can be corrected by reconstitution of

intestinal microbiota, but only if this occurs dur-

ing the neonatal period [11]. Prenatal exposure to

companion animals is linked with changes in mi-

crobiota and infantile pet exposure is negatively

associated with wheezy bronchitis at 24 months

of age [10].

An important question is how the microbiota

is altered by the significant changes in diet dur-

ing the first years of life, and how this affects in-

testinal immune development; the host-microbe

crosstalk during and after breastfeeding is criti-

Microbial concentration

(relative to total)

6 months 24 months

Age

Lactobacilli

Unculturables

Bifidobacteria

Coliforms

Clostridia

BacteroidesOthers

0 months Adults

Fig. 1. Relative changes in gut microbiota composition suggested by culture-dependent and cul-

ture-independent studies. The numbers of bifidobacteria can be influenced by diet, probiotics

and prebiotics.

Koletzko B, et al. (eds): Pediatric Nutrition in Practice. World Rev Nutr Diet. Basel, Karger, 2015, vol 113, pp 87–91
DOI: 10.1159/000360322