Variation of the Human Milk Bacterial Diversity during the Time of the Day

Many bacterial communities display oscillations throughout the day; it has been shown that in humans, the healthy gut microbiome also shows fluctuations in the abundance of bacterial community, related with feeding times and sleep cycles. Likewise, in human milk there are beneficial bacteria that undergo changes in the same time interval and are transferred to the newborn by breastfeeding, colonizing the gastrointestinal tract. The aim of this work was to identify changes in the bacterial diversity of human milk throughout the day. Human milk samples were collected from a single donor three times during the day (morning, afternoon, night) for 5 consecutive days, and bacterial DNA was extracted. Bacterial diversity was characterized by high-throughput DNA sequencing of 16S rDNA libraries, and taxonomy was assigned by comparison of sequences against a database. Finally, the significant differences in relative abundance and alpha and beta diversity were determined. The analysis of human milk displayed changes in the bacterial diversity during the day, with significant changes in the Shannon diversity index. Our data show that human milk seems to be affected by the daytime change, and these changes could influence the infant gut microbiota.