Pediatric Nutrition in Practice

88 Endo  Tang  Salminen

results in an altered intestinal microenvironment,
which influences the nature of subsequent intes-
tinal colonization.
In the newborn, initial colonization with facul-
tative anaerobes, enterobacteria, coliforms, pro-
teobacteria, lactobacilli and streptococci is rapidly
followed by colonization with anaerobic genera
such as Bifidobacterium , Bacteroides , Clostridium
and lactic acid bacteria. Although recent research
indicates that the interhost differences are much
less marked than previously thought, molecular
analyses demonstrate differences between the mi-
crobiota of formula-fed and breastfed infants with
respect to bifidobacterial numbers and species
composition. In breastfed infants, bifidobacteria
constitute 60–90% of the total fecal microbiota,
while lactobacilli comprise less than 1% [1, 4]. The
most common bifidobacterial species in breastfed
infants are B. longum , B. breve and B. infantis [5].
In formula-fed infants, the microbiota is more
complex and inf luenced by the formula composi-
tion – for instance, by reported overrepresentation
of Clostridium difficile and a higher richness in
species. Lactic acid bacteria composition in breast-
fed and formula-fed infants is similar (with some
geographic differences), with Lactobacillus casei
group microorganisms such as L. paracasei and
L. rhamnosus being common [unpubl. results].
Differences in microbiota between breastfed and
formula-fed infants have lessened with improved
infant formulae.

Gut Microbiota in the First Six Months of Life

Breastfeeding for 4–6 months will assist in the de-
velopment of healthy gut microbiota by provid-
ing bifidobacteria and lactic acid bacteria, which
reinforce colonization, and by supplying human
milk oligosaccharides, which promote a healthy
microbiota composition. Breastfeeding also facil-
itates the exchange of microbes between mother
and infant, since breast milk itself is a rich source
of bacteria. Of note, the breast milk microbiota in

mothers having a cesarian section differs from

that of mothers having a vaginal delivery [6].

Microbes are also exchanged via skin contact and

exposure to the microbiota in the immediate en-

vironment. Every individual has a unique, char-

acteristic microbiota during later phases of

breastfeeding that comprises a dynamic mixture

of microbes typical to each individual. Weaning,

introduction of solid foods, and antimicrobial

drug treatment will break the constant supply of

oligosaccharides and microbes from the mother,

thus affecting intestinal microbiota development.

Molecular analysis of bacterial communities

in healthy babies during the first 10 months of life

demonstrates progression from a simple profile

in the first days of life to a more complex, diverse

profile with members of the genera Bifidobacte-

rium , Ruminococcus , Enterococcus , Clostridium

and Enterobacter identified by 6 months of age

[1– 4]. Bifidobacterium and Ruminococcus species

dominate the intestinal microbiota with high-

level, stable expression over time. A Canadian

study on 4-month-old infants reported higher bi-

fidobacterial levels and lower clostridial numbers

in breastfed infants than in infants receiving for-

mula [14]. Ongoing improvements in formulae

have lessened these differences [7].

The healthy intestinal microbiota in infancy is

characterized by a large Gram-positive bacterial

population which contains significant numbers of

bifidobacteria, mainly B. longum , B. breve and B.

infantis. Lactic acid bacteria may play a role in pro-

viding the right intestinal environment for bifido-

bacteria to dominate. A healthy microbiota during

infancy is particularly important as this establish-

es the basis for healthy gut microbiota later in life.

Gut Microbiota in Infants from Six Months

Onward

After the first 6 months of life, the microbiota be-

comes more diverse [1, 6, 9]. Several studies have

examined the progression of microbiota from birth

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