Human milk microbial species are associated with infant head-circumference during early and late lactation in Guatemalan mother-infant dyads

Abstract

Human milk contains abundant commensal bacteria that colonize and establish the infant’s gut microbiome but the association between the milk microbiome and head circumference during infancy has not been explored. For this cross-sectional study, head-circumference-for-age-z-scores (HCAZ) of vaginally delivered breastfed infants were collected from 62 unrelated Mam-Mayan mothers living in eight remote rural communities in the Western Highlands of Guatemala during two stages of lactation, ‘early’ (6–46 days postpartum, n = 29) or ‘late’ (109–184 days postpartum, n = 33). At each stage of lactation, infants were divided into HCAZ ≥ −1 SD (early: n = 18; late: n = 14) and HCAZ < −1 SD (early: n = 11; late: n = 19). Milk microbiome communities were assessed using 16S ribosomal RNA gene sequencing and DESeq2 was used to compare the differential abundance (DA) of human milk microbiota with infant HCAZ subgroups at both stages of lactations. A total of 503 ESVs annotated 256 putative species across the 64 human milk samples. Alpha-diversity using Chao index uncovered a difference in microbial community richness between HCAZ ≥ −1 SD and HCAZ < −1 SD groups at late lactation (p = 0.045) but not at early lactation. In contrast, Canonical Analysis of Principal Coordinates identified significant differences between HCAZ ≥ −1 SD and HCAZ < −1 SD at both stages of lactation (p = 0.003); moreover, 26 milk microbial taxa differed in relative abundance (FDR < 0.05) between HCAZ ≥ −1 SD and HCAZ < −1 SD, with 13 differentially abundant at each lactation stage. Most species in the HCAZ ≥ −1 SD group were Streptococcus species from the Firmicutes phylum which are considered human colonizers associated with human milk whereas the HCAZ < −1 SD group at late lactation had more differentially abundant taxa associated with environmentally and ‘potentially opportunistic’ species belonging to the Actinobacteria genus. These findings suggest possible associations between brain growth of breastfed infants and the milk microbiome during lactation. Importantly, these data provide the first evidence of cross talk between the human milk microbiome and the infant brain that requires further investigation.

Human milk microbiome: associations with maternal diet and infant growth

“…A limited number of studies had previously reported associations between maternal nutrient intakes during lactation that had uncovered both multiple positive and negative associations with the HMM at the phylum and genus levels using correlation and cluster analyses ( 23 – 26 ). Since associations between the HMM and maternal nutrient intakes with infant growth parameters had not been explored, we also investigated associations of maternal nutrient intakes with previously established DA species that differed between infants with ‘normal infant z-scores’ defined as WAZ ≥ −1SD, LAZ ≥ 1.5SD, and HCAZ ≥ −1SD compared with infants experiencing growth faltering defined as mildly underweight (WAZ < −1SD), mildly stunted (LAZ < −1.5SD), and with smaller head circumferences (HCAZ < −1SD) by the stage of lactation ( 44 , 45 ). Moreover, given that human milk continuously provides an infant with a dynamically changing community of commensal and potentially beneficial bacteria that differs between early and late lactation ( 43 ), we conducted our analyses at the species level during both early and late lactation.…”

“…Recently, we reported differences in the HMM between infants with normal growth and infants with mild growth faltering ( 44 , 45 ). We identified 30 differentially abundant (DA) taxa between the LAZ groups [mildly stunted (LAZ < −1.5SD) versus the non-stunted (LAZ ≥ −1.5SD)], 23 DA taxa between the WAZ groups [normal weight (WAZ ≥ −1SD) versus the mildly underweight (WAZ < −1SD)], and 26 DA taxa were identified between HCAZ groups [normal HC (HCAZ ≥ −1 SD) versus the smaller HC (HCAZ < −1 SD)] ( 44 , 45 ).…”

“…Recently, we reported differences in the HMM between infants with normal growth and infants with mild growth faltering ( 44 , 45 ). We identified 30 differentially abundant (DA) taxa between the LAZ groups [mildly stunted (LAZ < −1.5SD) versus the non-stunted (LAZ ≥ −1.5SD)], 23 DA taxa between the WAZ groups [normal weight (WAZ ≥ −1SD) versus the mildly underweight (WAZ < −1SD)], and 26 DA taxa were identified between HCAZ groups [normal HC (HCAZ ≥ −1 SD) versus the smaller HC (HCAZ < −1 SD)] ( 44 , 45 ). Our present study aimed to assess the association between maternal nutrient intakes and the DA HMM taxa identified at early and late lactation between infants with normal growth compared with infants with mild growth faltering among exclusively breastfed mother–infant dyads.…”

Potential Epigenetic Effects of Human Milk on Infants’ Neurodevelopment

“…A recent cross-sectional study was carried out to examine the correlation between the milk microbiome and neurodevelopment, specifically focusing on head circumference-for-age z-scores (HCAZ) in breastfed infants [ 110 ]. Significant differences in the milk microbiota composition were found between infants with HCAZ ≥ −1 SD and HCAZ < −1 SD at both early (≤46 days postpartum) and late stages of lactation (109–184 days postpartum).…”

“…The HCAZ ≥ −1 SD group had a higher abundance of Streptococcus species associated with human milk, while the HCAZ < −1 SD group, particularly at the late stage of lactation, exhibited a higher abundance of differentially abundant taxa associated with environmentally and potentially opportunistic species. These findings suggest a potential association between the milk microbiome and brain growth in breastfed infants during lactation, necessitating, however, further investigation into the interplay between the human milk microbiome and infant neurodevelopment [ 110 ].…”