Contributions of the maternal oral and gut microbiome to placental microbial colonization in overweight and obese pregnant women

Abstract

A distinct bacterial signature of the placenta was reported, providing evidence that the fetus does not develop in a sterile environment. The oral microbiome was suggested as a possible source of the bacterial DNA present in the placenta based on similarities to the oral non-pregnant microbiome. Here, the possible origin of the placental microbiome was assessed, examining the gut, oral and placental microbiomes from the same pregnant women. Microbiome profiles from 37 overweight and obese pregnant women were examined by 16SrRNA sequencing. Fecal and oral contributions to the establishment of the placental microbiome were evaluated. Core phylotypes between body sites and metagenome predictive functionality were determined. The placental microbiome showed a higher resemblance and phylogenetic proximity with the pregnant oral microbiome. However, similarity decreased at lower taxonomic levels and microbiomes clustered based on tissue origin. Core genera: Prevotella, Streptococcus and Veillonella were shared between all body compartments. Pathways encoding tryptophan, fatty-acid metabolism and benzoate degradation were highly enriched specifically in the placenta. Findings demonstrate that the placental microbiome exhibits a higher resemblance with the pregnant oral microbiome. Both oral and gut microbiomes contribute to the microbial seeding of the placenta, suggesting that placental colonization may have multiple niche sources.

Lack of evidence for microbiota in the placental and fetal tissues of rhesus macaques

“…It was detected in a preliminary molecular survey of the fetus and placenta of the Japanese macaque (85) and it has also been reported in numerous DNA sequence-based investigations of the human placenta (31–38, 41–43). However, Staphylococcus has also been identified as a background DNA contaminant in sequence-based studies (48), including in several prior studies of the human placenta (39, 57, 62). In the current study, the prominent ASV classified as Staphylococcus was also prominent and widespread among the background technical control samples, suggesting that it was a background DNA contaminant in this study as well.…”

Functional characterization ofRalstonia insidiosa, a bona fide resident at the maternal-fetal interface

“…Whether there are microbiota (live or simply DNA signatures) in the maternal-fetal interface remains mired in controversy. In the recent years, there has been a large number of studies, providing both sequencing and histological evidence, indicating microbial signatures 3,11,18,19,22,23,29 , while other studies have reported these signatures as likely DNA contaminants originating from the sample collection and/or the DNA extraction process, rather than the placenta itself [54][55][56][57] . Placenta location remains a key variable in the aforementioned studies given that that BP, PV and FM have distinct physiology and function.…”

“…How bacteria reach the placenta has not been fully determined. Several studies have reported that non-pathogenic microbes in the placenta are most similar to those found in the oral mucosa 18,29,48 . For example, the oral bacterium Fusobacterium nucleatum has been isolated from the placenta and amniotic fluid 49 .…”

“…Seferovich and colleagues further validated the presence of bacteria from term and preterm placentas, without evidence of maternal infection, using 16S in situ hybridization, histologic staining methods, and clinical culturing methods 22 . Additionally, several investigators have used culture-independent sequencing methods to identify bacterial DNA in term and preterm human placentas 18,22,25,26 and other fetal or maternal conditions including low birth-weight 27 , preeclampsia 28 , maternal obesity 29 , and gestational diabetes 30 .…”

The matter of the reproductive microbiome

“…Timing Affected microbiome Maternal diet 19,94 Preconception Gut Antibiotics 95 Preconception Gut BMI 42,86,96,97 Preconception Gut, meconium (vaginal delivery) Overweight / obesity 96,98,99 Preconception Gut Diabetes mellitus 100 Preconception Meconium Pregnancy 34,35,37,40,41 Pregnancy Gut, vagina Maternal diet 19,101 Pregnancy Gut, placenta, meconium Probiotics 101,102 Pregnancy Placenta, meconium, Vagina Overweight/obesity 42,45,46 Pregnancy Gut Gestational diabetes 100,103 Gut, placenta, meconium Gestational weight gain 19,42,45,96 Pregnancy Gut, placenta Chorioamnionitis 4,66,104 Pregnancy Placenta, amniotic fluid…”