Methods: Mother-infant pairs from diverse backgrounds were recruited and oral bacterial acquisition was monitored bimonthly from birth to age one year. Saliva samples were collected from infant-mother pairs, and plaque samples were collected from infants after tooth eruption. For 125 samples from 9 families, bacterial species and genera were identified by pyrosequencing of 16S rRNA genes. Changes in bacterial levels and community diversity over time were analyzed using linear mixed-effects models (LMMs) and multivariate statistics.
Results: Increases in microbial community diversity at the species level were observed over the first year of life for infant saliva samples (n=63, p=0.017, LMM for Shannon diversity). An analysis of prevalence showed an ordered pattern of species acquisition. The S. mitis group were initial colonizers followed by species of Gemella, Rothia, other streptococci and Veillonella. More complex communities then developed after tooth eruption. An analysis of relative levels of species in infants demonstrated significant changes over the 12 months in 5 species. In contrast, mothers’ microbial communities were stable over time (n=24). The salivary communities from infants became more similar to each others’ and to adult communities over time.
Conclusions: The developing infant oral microbiome follows a program of increasing diversity, specifically ordered acquisition of species, and converging similarity among individuals. The clinical relevance of this research will be to inform preventive and treatment strategies based on the assembly of health-promoting bacterial communities.