Having older siblings is associated with gut microbiota development during early childhood

Abstract

Background: Evidence suggests that early life infections, presence of older siblings and furred pets in the household affect the risk of developing allergic diseases through altered microbial exposure. Recently, low gut microbial diversity during infancy has also been linked with later development of allergies. We investigated whether presence of older siblings, furred pets and early life infections affected gut microbial communities at 9 and 18 months of age and whether these differences were associated with the cumulative prevalence of atopic symptoms of eczema and asthmatic bronchitis at 3 years of age. Bacterial compositions and diversity indices were determined in fecal samples collected from 114 infants in the SKOT I cohort at age 9 and 18 months by 16S rRNA gene sequencing. These were compared to the presence of older siblings, furred pets and early life infections and the cumulative prevalence of diagnosed asthmatic bronchitis and self-reported eczema at 3 years of age.

Results: The number of older siblings correlated positively with bacterial diversity (p = 0.030), diversity of the phyla Firmicutes (p = 0.013) and Bacteroidetes (p = 0.004) and bacterial richness (p = 0.006) at 18 months. Further, having older siblings was associated with increased relative abundance of several bacterial taxa at both 9 and 18 months of age. Compared to the effect of having siblings, presence of household furred pets and early life infections had less pronounced effects on the gut microbiota. Gut microbiota characteristics were not significantly associated with cumulative occurrence of eczema and asthmatic bronchitis during the first 3 years of life.

Conclusions: Presence of older siblings is associated with increased gut microbial diversity and richness during early childhood, which could contribute to the substantiation of the hygiene hypothesis. However, no associations were found between gut microbiota and atopic symptoms of eczema and asthmatic bronchitis during early childhood and thus further studies are required to elucidate whether sibling-associated gut microbial changes influence development of allergies later in childhood.

Fig. 1

Boxplots comparing bacterial diversity and richness at 9 months (white color) and 18 months (grey color) between individuals with or without older siblings (a, b), furred pets (c, d) and early life infections (e, f). Boxes show 25^th to 75^th percentiles and whiskers indicate minimum to maximum values. Statistical significance was evaluated by Mann Whitney test, using p < 0.05 as measure of significance. ns = not significant, however p-values below 0.1 are shown

Fig. 2

Scatter plots illustrating the bacterial diversity (a), richness (b) and phyla diversities of Firmicutes (c) and Bacteroidetes (d) in infants at 18 months of age divided into groups according to the number of older siblings in the household. Red lines indicate mean ± standard deviation. Spearman’s correlations coefficient rho and p-value (p < 0.05 as a measure of significance) are shown

Fig. 3

Correlation matrices relating relative abundance of bacterial genera at 9 months (a) and 18 months (b) to the presence of older siblings, furred pets and early life infections. Scale indicate the Spearman’s rank correlation coefficient rho, ranging from −0.5 (negative correlation; red color) to 0.5 (positive correlation; blue color). Black dots indicate statistically significant correlations with FDR adjusted p-value < 0.1

Fig. 4

Principle Component Analysis plots of relative abundance of gut bacterial families at 9 (a) and 18 months of age (b). Green triangles indicate no eczema or asthmatic bronchitis, orange squares indicate presence of eczema, blue triangles indicate presence of asthmatic bronchitis and red circles indicate presence of both asthmatic bronchitis and eczema