Quantitative Differences in the Human Intestinal Microbiota Through the Stages of Life: Infants, Children, Adults and the Elderly

The aim of this study was to compare the human intestinal microbiota in different age groups, elucidating the precise stages of life in which the gut microbiota evolves its specific characteristics in terms of composition and diversity, as well as associating different bacterial groups for prediction of their intertwined metabolic role, considering their importance in human health. The quantitative composition, Bacteroidetes/Firmicutes (B/F) ratio, counts and diversity indices of faecal samples obtained from infant, child, adult and elderly individuals were assessed via quantitative real-time polymerase chain reaction (qPCR). The intestinal microbiota of infants expressed the highest B/F ratio and diversity. The total bacteria counts, Bacteroides-Prevotella and Blautia coccoides-Eubacterium rectale groups were the most abundant in adults and infants, while child and elderly individuals presented the highest counts of Firmicutes and Lactobacillus sp. In infants, the counts of Enterococcus sp., Streptococcus sp., Enterobacteriaceae, Veillonella sp. and Clostridium perfringens groups were higher, when compared to the other age groups. The tightest positive correlations between bacteria within age groups were found for the B. coccoides-E. rectale, C. leptum (incl. Faecalibacterium prausnitzii), Bacteroidetes-Prevotella and Atopobium groups. Through the stages of life, the quantitative composition and diversity of intestinal microbiota evolves with two changing maximal peaks of predominant groups, with bacterial diversity decreasing from infant to child stage, showing unitary stabilization in adults and presenting a wide individual range in the elderly. The high counts of Bacteroidetes and Clostridium from the phylum Firmicutes, present throughout all life stages, mainly influence the composition and metabolic activity of other bacteria. Recognizing age-specific differences may provide a basis for comparing different geographic populations and predicting the intertwined metabolites of various bacteria, which have certain implications for health.