Human Breast Milk Microbiota is Influenced by Maternal Age and BMI, Stage of Lactation and Infant Feeding Practices

Abstract

BackgroundHuman breast milk contains a diverse population of bacteria, but factors influencing the milk microbiota have not been described.ObjectiveWe explored if maternal age, BMI, stage of lactation and infant feeding practices influenced bacterial communities in breast milk of indigenous mothers in the western highlands of Guatemala.MethodsIn this cross‐sectional study, unilateral milk samples were collected from Mam‐Mayan women during early (5‐46d, n=33) or established (4‐6mo, n=43) lactation. Maternal age, BMI and feeding practices (exclusive, predominant and mixed feeding) were recorded. Milk bacterial communities were characterized by 16S ribosomal RNA amplicon sequencing using Illumina MiSeq platform. Sequence treatment, taxonomy assignment and operational taxonomic unit counts were performed with customized scripts based on Mothur and Dada2 MiSeq protocols. Taxonomy assignment was based on a >95% confidence threshold. We compared normal (BMI 18.5–24.9) vs. overweight (BMI 25–30), early vs. established lactation and exclusive/predominant breastfeeding vs. mixed feeding. For all statistical tests, an effect size >1.0, a confidence interval >95% and a p‐value and q‐value <0.05 were considered significant.ResultsHuman milk bacterial community was altered by maternal BMI, stage of lactation, infant feeding practices whereas bacterial diversity was only affected by maternal age. The highest bacterial diversity occurred in mothers aged 22–24 (Shannon index 1.8) and the lowest bacterial diversity occurred in mothers aged 13–15 (Shannon index 1). At the phylum level, stage of lactation modified the proportion of Firmicutes and Proteobacteria. Firmicutes was >20% higher in early lactation and Proteobacteria was 30% higher in established lactation. A normal BMI was associated with higher proportions of Alphaproteobacteria and Betaproteobacteria at the class level. At the family level, exclusive/predominant breastfeeding when to compared to mixed feeding was associated with higher proportions of Corynebacteriaceae, Lactobacillaceae and Rhodobacteraceae.ConclusionHuman breast milk bacterial communities are determined by a complex interplay of maternal factors, stage of lactation and infant feeding practices. Exclusive breastfeeding might be necessary for the shaping of a healthy microbiota in the nursing infant. Finally, our data demonstrate the need to better understand the factors that contribute to the establishment of human breast milk microbiota, which could in turn influence infant growth and development.Support or Funding InformationNatural Sciences and Engineering Research Council of Canada (NSERC)