Human Milk Microbiota in an Indigenous Population Is Associated with Maternal Factors, Stage of Lactation, and Breastfeeding Practices

Abstract

Background: Human milk contains a diverse community of bacteria that are modified by maternal factors, but whether these or other factors are similar in developing countries has not been explored. Our objective was to determine whether the milk microbiota was modified by maternal age, BMI, parity, lactation stage, subclinical mastitis (SCM), and breastfeeding practices in the first 6 mo of lactation in an indigenous population from Guatemala.

Methods: For this cross-sectional study, Mam-Mayan indigenous mothers nursing infants aged <6 mo were recruited. Unilateral human milk samples were collected (n = 86) and processed for 16S rRNA sequencing at the genus level. Microbial diversity and relative abundance were compared with maternal factors [age, BMI, parity, stage of lactation, SCM, and 3 breastfeeding practices (exclusive, predominant, mixed)] obtained through questionnaires.

Results: Streptococcus was the most abundant genus (33.8%), followed by Pseudomonas (18.7%) and Sphingobium (10.7%) but relative abundance was associated with maternal factors. First, Lactobacillus and Streptococcus were more abundant in early lactation whereas the common oral (Leptotrichia) and environmental (Comamonas) bacteria were more abundant in established lactation. Second, Streptococcus,Lactobacillus,Lactococcus,Leuconostoc, and Micrococcus had a higher abundance in multiparous mothers compared with primiparous mothers. Third, a more diverse microbiota characterized by a higher abundance of lactic acid bacteria (Lactobacillus,Leuconostoc, and Lactococcus), Leucobacter, and Micrococcus was found in mothers with a healthy BMI. Finally, distinct microbial communities differed by stage of lactation and by exclusive, predominant, or mixed breastfeeding practices.

Conclusion: Milk bacterial communities in an indigenous community were associated with maternal factors. Higher microbial diversity was supported by having a healthy BMI, the absence of SCM, and by breastfeeding. Interestingly, breastfeeding practices when assessed by lactation stage were associated with distinct microbiota profiles.

Keywords: 16S rRNA sequencing; Mam-Mayan; exclusive breastfeeding; indigenous; microbial diversity; milk microbiota; predominant breastfeeding.

FIGURE 1

A) Human milk microbiota diversity based on pooled samples from all mothers, illustrated as relative abundance along major taxonomic levels. Total counts for each taxonomic unit are specified between parentheses (in million). Only taxonomic units with a total count >100,000 are accounted for in the legends. B) Major clades including weighted nodes (genera >100,000 counts) as analyzed in the human milk microbiota. The 9 most abundant genera are identified.

FIGURE 2

Distance-based redundancy analysis (db-RDA or CAP) ordination representations (Bray distance) for A) maternal age; B) maternal BMI; C) parity; D) stage of lactation; E) Infant feeding practices; and F) SCM. Significant clustering of groups was found for maternal BMI, parity, and stage of lactation (ANOVA), P <0.05. EBF, exclusive breastfeeding; PBF, predominant breastfeeding; SCM, subclinical mastitis.

FIGURE 3

Differential abundance plots for each maternal factor: A) maternal age (adult versus adolescent); B) maternal BMI (healthy weight versus overweight); C) parity (primiparous versus multiparous); D) stage of lactation (early versus established); E) breastfeeding practices (exclusively/predominant breastfeeding versus mixed feeding); and F) SCM (yes or no). Each plot shows fold change for the differentially abundant taxonomic units (group size fixed to a minimum of 10 and effect size to a fold change of 5). Error bars represent the SE on the estimated fold change. EBF, exclusive breastfeeding; PBF, predominant breastfeeding; SCM, subclinical mastitis.

FIGURE 4

Comparison at genera level by lactation stage and breastfeeding practices. Centroide crosses represent the shift of each group and their distinct cluster. Early lactation clusters differently than established; predominant and mixed feeding cluster higher on the y-axis scale than exclusive breastfeeding.