Table 4.

The dominant populations of infant gut microbiota.

Microbes	Key description	Refs.
Bifidobacteria	Bifidobacteria make a major metabolic contribution to their host through the degradation of diet-derived glycans and host-provided carbohydrates (known as host glycans and including mucins and HMOs).	(123)
Clostridia class	They are known as pathogenic microorganisms that may cause bacteremia and pseudomembranous colitis, and their presence at high densities is interpreted as an indicator of an unhealthy microbiota.	(124)
Genus Bacteroides	Members of this genus are classified as saccharoclastic bacteria that are able to metabolize host-produced glycans, such as HMOs and mucins, but also complex plant polysaccharides such as starch, cellulose, xylans, and pectins.	(125, 126)
Genera Veillonella	These bacteria are saccharolytic and utilize end products of carbohydrate fermentation (e.g., lactate) of other infant gut bacteria, such as Streptococcus spp. and Bifidobacterium spp., to produce propionate, forming an important trophic chain.	(127)
Genera Streptococcus	They are among the first established bacteria in the infant gut, where they can be identified within the first 24 h following birth.	(128)
Genus Collinsella	Members of the genus Collinsella have recently been shown to reach high numbers when they are associated with an infant gut microbiota dominated by bifidobacteria.	(129)
Genus Lactobacillus	Vertical transmission of Lactobacillus species presents the origin of infant Lactobacillus microbiota component. And they may be related to the HMO metabolism of infants.	(128)
Genus Akkermansia	They can provide a barrier for the baby’s intestines and may participate in the fermentation of HMO.	(130)