Stepwise establishment of the microbiota: opportunities of modulation

The microbiota of a newborn develops rapidly after birth and it is initially strongly dependent on the mother’s microbiota, mode of delivery and birth environment. The microbiota of the mother is determined by genetic and environmental factors. It has been demonstrated that also stress and dietary habits during late pregnancy and prior to birth may have a significant impact on the microbiota at the time of delivery, thus influencing the quality and quantity of first colonisers of the newborn. Subsequent feeding practices, including formula feeding and breastfeeding, and the home environment of the infant influence the microbiota, both at the level of species composition and concentrations of bacteria. Factors such as antibiotic use by the mother of the infant modulate specific groups of microbiota and may both modulate microbiota and enhance the presence of antibiotic resistance genes among the developing gut microbiota. Thus, beneficial means of modulation are an important focus area.

Succession of microbial communities

The step-wise process of establishing culturable indigenous microbiota begins with facultative anaerobes such as the Enterobacteria, coliforms, Lactobacilli and Streptococci first colonizing the intestine. These are rapidly succeeded by Bifidobacteria and lactic acid bacteria.
The following steps can be described:

1) Early colonization at birth with facultative anaerobes depending on themode of delivery.
2) Rapid succession by anaerobic genera such as Bifidobacterium, Bacteroides, Clostridium and Eubacterium.
3) Enhanced diversity in composition through weaning.
4) Approaching mature intestinal microbiota.

New molecular methods indicate that Bifidobacteria can range from 60 up to 90 % of the total faecal microbiota in breast-fed infants. In formula-fed infants the microbiota is more complex, but depends on the composition of the formula.

The new techniques indicate that the greatest difference in the microbiota of breast-fed and formula-fed infants lies both in the bifidobacterial numbers and species composition within the intestinal microbiota, while the lactic acid bacteria composition appears to be rather similar. Bifidobacterium breve, Bifidobacterium infantis and Bifidobacterium longum are frequently found in faecal samples of breast-fed infants, whereas the most common Lactobacilli in breast-fed and formula-fed infant faeces constitute Lactobacillus acidophilus group microorganisms such as L. acidophilus, L. gasseri and L. Johnsonii. However, depending on the transfer of microbiota from the mother and the immediate environment of the infant, other lactic acid bacteria may become common. In general, the differences between the breast-fed and formula-fed infants have decreased along with the development of the improved composition of infant formulas.

The potential for microbiota modulation via formula components has improved and offers new opportunities for the future. Characterisation of the composition and function of the intestinal microbiota has presented considerable methodological difficulties and thus our understanding has improved slowly.

Deviations in composition and activity and disturbed succession of the microbiota during early infancy have been linked to the risk of developing infectious, inflammatory and allergic diseases later in life. Assisting healthy microbiota development and maintaining an established healthy microbiota are important goals for infant feeding. Some points of intervention are included in Figure 1, together with the nutritional factors that also need to be considered.

Figure 1. Microbiota development and points for modulation


Weaning and gut microbiota

The practice of breastfeeding for 4-6 months has been considered to promote the development of a healthy gut microbiota. A healthy breastfed infant remains the target model. Major changes in the microbiota composition during breastfeeding are related to breastmilk components, especially galacto-oligosaccharides, but also other nutrients in breastmilk.

These factors are influenced by genetic factors and the diet of the mother. Breastfeeding also provides an optimal environment for the exchange of microbes between mother and infant, including contact with the mother’s skin and exposure to microbiota present in the immediate environment. As a result, every individual has a unique characteristic microbiota during the later phases of breastfeeding.

The intestinal microbiota as a defined entity does not exist but this population comprises a dynamic mixture of microbes typical to each individual and varying within an individual ranges over time.

Weaning and the introduction of solid foods as well as anti-microbial drug treatment periods will break the contact and constant supply of oligosaccharides and microbes from the mother. Thus, microbiota modulation remains an important target after weaning and should be considered when choosing or developing weaning foods and their components.

The basic target is a complex microbial community that provides a barrier against foreign microbes and functions as that of the healthy breast-fed infant. Additionally, this process creates the basis for the establishment of a ‘non-inflammatory’ status of the gut. Such an environment in infants is defined by a large Gram-positive bacterial population with a significant number of bifidobacteria in a species composition typical to the healthy breast-fed infant (mainly B. longum, B. breve and B. infantis). Lactic acid bacteria may have a role in providing the right conditions for Bifidobacteria to dominate. The collective composition of the colonising strains in infancy also establishes the basis for a healthy gut microbiota later in life, since the development of the disease-free state of the gut lies in the right host-microbe interaction in infancy.

References

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