Human Milk Microbiota Across Lactation Stages and Free Glutamate Concentrations in Healthy Ecuadorian Women

<b>Background/Objectives:</b> There is limited information on human milk (HM) microbiome composition and function in Latin America. Also, interactions between HM constituents and its microbiome have received partial attention. Objective: To characterize the HM microbiota composition considering lactation stages (colostrum, transition, and mature HM) and free glutamate concentrations in Ecuadorian mothers. <b>Methods:</b> We recruited 20 mothers that gave birth to normal full-term babies and donated colostrum, transition, and mature milk. Samples were assessed by 16S rRNA gene sequencing by Oxford Nanopore Technologies (ONT). Free glutamate concentrations were measured by proton nuclear magnetic resonance (NMR) spectroscopy. <b>Results:</b> For each lactation stage and in order of frequency, the majority of ASVs were assigned to <i>Staphylococcus</i>, <i>Streptococcus</i>, (Firmicutes); <i>Escherichia</i>, <i>Acinetobacter</i>, (Proteobacteria); <i>Corynebacterium</i>, <i>Lactobacillus</i>, <i>Cutibacterium</i>, (Actinobacteriota); <i>Chryseobacterium</i>, and <i>Flavobacterium</i> (Bacteroidota). Alfa diversity was similar in HM samples and tended to be higher in milk intended for male infants. We observed significant differences in qualitative β-diversity metrics between samples with low and high glutamate concentrations. Functional predictions of HM microbiota demonstrated the presence of polyamine biosynthesis II super pathway in samples with high glutamate concentrations. <b>Conclusions:</b> The core bacterial components of the HM microbiota in Ecuadorian women were similar to those reported from different parts of the world, with variations at the genus level. Free glutamate dynamics in HM need to be studied considering maternal production and bacterial metabolism to better understand HM composition for optimal infant nutrition.