Origins of human milk microbiota: new evidence and arising questions

Abstract

Human milk contains a diverse community of bacteria. The growing appreciation of commensal microbes and increasing availability of high-throughput technology has set the stage for a theory-driven approach to the study of milk microbiota, and translation of this knowledge to improve maternal and child health. We recently profiled the milk microbiota of healthy Canadian mothers and applied theory-driven causal modeling, finding that mode of breast milk feeding (nursing directly at the breast vs. pumping and feeding breast milk from a bottle) was significantly associated with milk microbiota composition. This observation could reflect an increased exposure to pumps and/or a decreased exposure to the infant mouth. Either way, it provides evidence for the retrograde mechanism of milk inoculation. Here, we discuss the implications of this research and related controversies, and raise new questions about the origins and function of milk bacteria.

Early‐Life Gut Microbiome—The Importance of Maternal and Infant Factors in Its Establishment

“…Clinical studies demonstrating ingested probiotic strains were identified in maternal breast milk further support this hypothesis 85,86 . More information about the origin of milk microbes can be found in this review by Moossavi et al 87 …”

Breast-Milk Microbiota Linked to Celiac Disease Development in Children: A Pilot Study From the PreventCD Cohort

“…Species belonging to the Methylobacterium genus are prevalent in water pipes and reservoirs (Barbeau et al, 1996;Vaz-Moreira et al, 2017) and as contaminants of industrial milk samples (Bracke et al, 2014). In addition, some studies also indicate that Methylobacterium species are part of the human oral and skin microbiota (Hung et al, 2011;Alekseyenko et al, 2013) and, therefore, their presence in breast milk microbiota could partly be due to their transmission via the infant's oral cavity, an event that has been recently hypothesized as important modulator of the hMM (Moossavi and Azad, 2019;. Interestingly, a recent microbiota analysis of human breast tissue through 16S rRNA gene amplicon sequencing has also reported the presence of Methylobacterium (among other environmental microbes such as Ralstonia) in healthy and cancerous breast biopsies (Costantini et al, 2018), supporting the presence of these type of microbes in human breast-related samples.…”

Formula Diet Alters the Ileal Metagenome and Transcriptome at Weaning and during the Postweaning Period in a Porcine Model

“…Limitations of the current study included the fact that the human milk fed to piglets represented a pool of donor milk. The interindividual variations of milk composition between donor mothers, including fatty acids ( 71 ), metabolites ( 72 ), oligosaccharides ( 73 ), and microbiota ( 74 ), might alter intestinal metagenome and transcriptome. However, the pooled HM used in the current study likely eliminated the impact of interindividual variations of HM on intestinal functions in piglets.…”