Alzheimer’s disease (AD) is a multifactorial pathology characterized by β-amyloid (Aβ) deposits, Tau hyperphosphorylation, neuroinflammatory response, and cognitive deficit. Changes in the bacterial gut microbiota (BGM) have been reported as a possible etiological factor of AD. We assessed in offspring (F1) 3xTg, the effect of BGM dysbiosisdysbiosis in mothers (F0) at gestation and F1 from lactation up to the age of 5 months on Aβ and Tau levels in the hippocampus, as well as on spatial memory at the early symptomatic stage of AD. We found that BGM dysbiosisdysbiosis with antibiotics (Abx) treatment in F0 was vertically transferred to their F1 3xTg mice, as observed on postnatal day (PD) 30 and 150. On PD150, we observed a delay in spatial memory impairment and Aβ deposits, but not in Tau and pTau protein in the hippocampus at the early symptomatic stage of AD. These effects are correlated with relative abundance of bacteria and alpha diversity, and are specific to bacterial consortia. Our results suggest that this specific BGM could reduce neuroinflammatory responses related to cerebral amyloidosis and cognitive deficit and activate metabolic pathways associated with the biosynthesis of triggering or protective molecules for AD.

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.