Abstract
The human oral cavity is sterile prior to birth, and we have limited knowledge of how complex oral communities are assembled. To examine bacterial acquisition and community assembly over the first year of life, oral samples from a cohort of nine infants and their mothers were collected, and bacterial community composition was studied by 16S rRNA gene sequencing. Exogenous species including skin and environmental bacteria were present initially, but were quickly replaced by a small, shared microbial community of species common to all infants and adults. Subsequent ordered microbial succession and the formation of increasingly complex communities was observed. By one year of age oral microbial community composition converged to a profile that was remarkably similar among children. The introduction of new nutrient sources, but not tooth eruption, was associated with increasing complexity. Infants had fewer species than mothers, mostly accounted for by the lack of certain anaerobes, and showing that the acquisition and assembly of oral microbial communities continues past infancy. When relative abundance was considered, a shared set of species accounted for the majority of the microbial community at all ages, indicating that the dominant structure of the oral microbiome establishes early, and suggesting that it persists throughout life.
Highlights
The individual adult human oral cavity typically hosts more than 200 species of bacteria, and over 600 species are commonly found in the broader adult population[1,2]
This study revealed that the oral microbiota is acquired in an ordered sequence and time course that was shared among infants (Fig. 4). This has previously been observed in the human infant gut, where the phylogenetic diversity increases gradually over time, and community assembly occurs as an orderly succession[19] that resembles the profile of the adult gastrointestinal tract[20]
Most of these are common in adults, but some species were more common in the infants than in mothers, including S. peroris, and uncultivated Leptotrichia Arg j44, Porphyromonas HF001, and possibly Leptotrichia FP036
Summary
The individual adult human oral cavity typically hosts more than 200 species of bacteria, and over 600 species are commonly found in the broader adult population[1,2]. A 16S rRNA gene-based study with resolution at the genus level showed that by the age of 4 months complex communities containing organisms typically present in adults are detected, including Streptococcus, Veillonella, and Neisseria species[5]. Older cultivation-based studies have tracked the acquisition of key species, including Streptococcus mitis, an early colonizer[8,9], and Streptococcus sanguinis[10], a late colonizer. More comprehensive cultivation-based studies have tracked the sequential assembly of early oral bacterial communities[13], and have suggested microbial dependencies and succession. These studies did not provide the resolution and comprehensiveness of newer 16S-based approaches, or provide a clear outline of the development of the infant oral microbiota. To examine oral bacteria acquisition and community assembly over the first year of life, we collected samples from a cohort of nine healthy infants and their mothers and studied their oral communities by 16S rRNA gene sequencing
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