Shared and non-shared sIgA-coated and uncoated bacteria in intestine of mother-infant pairs

Background: The infant gut microbiota is critical for promoting and maintaining early life health. Bacteria coated by secretory immunoglobulin A (sIgA) may help commensal bacteria colonize the gastrointestinal tract. The study aimed to analyze the composition of sIgA-coated and sIgA-uncoated bacterial communities at genus level, and lactobacilli and bifidobacterial communities at species level in human breast milk (HBM), infant, and maternal feces. Results Eleven pregnant women were recruited successfully. HBM, infant feces during colostrum, transition, and mature stages, and maternal feces within the mature stage were collected. sIgA-coated and sIgA-uncoated bacteria were separated with magnetic-activated cell sorting. Then 16S rRNA sequencing, bifidobacterial groEL gene sequencing, and lactobacilli groEL gene sequencing were performed to analyze the bacterial community. The richness of sIgA-coated bacteria was significantly higher than that of sIgA-uncoated bacteria in HBM. PCoA revealed that the compositions of sIgA-coated and sIgA-uncoated bacteria were different among HBM, infant and maternal feces. The dominant sIgA-coated bacteria in those samples were Escherichia/shigella and the dominant sIgA-uncoated bacteria was Pseudomonas . Higher relative abundance of sIgA-uncoated Bifidobacterium was found in the three lactation stages in infant feces compared to the corresponding HBM, and a higher relative abundance of sIgA-uncoated Faecalibacterium was found in maternal feces compared to HBM and infant feces. For the bifidobacterial community, PCoA analysis revealed a significantly different Bifidobacterium composition only in the sIgA-uncoated segments of infant feces and maternal feces. sIgA-coated and sIgA-uncoated B. longum subsp. infantis and B. pseudocatenulatum was dominant in infant feces and maternal feces, respectively. Additionally, the relative abundance of sIgA-uncoated B. longum subsp. infantis was significantly higher in infant feces compared to that in maternal feces. For the Lactobacillus community, the composition was significantly different in infant and maternal feces, while at species level, L . paragasseri and L . mucosae were dominant in infant and maternal feces, respectively. Conclusion HBM, infant, and maternal feces showed distinct diversity and composition of both sIgA-coated and sIgA-uncoated bacteria at genus level. Infant and maternal feces showed similar diversity and similar composition of Bifidobacterium at species level. The same Bifidobacterium species could be detected both in sIgA-coated and sIgA-uncoated form.