Human Endometrial Microbiota at Term of Normal Pregnancies

Abstract

The endometrium is a challenging site for metagenomic analysis due to difficulties in obtaining uncontaminated samples and the limited abundance of the bacterial population. Indeed, solid correlations between endometrial physio-pathologic conditions and bacteria compositions have not yet been firmly established. Nevertheless, the study of the endometrial microbiota is of great interest due to the close correlations between microbiota profiles, women’s health, and successful pregnancies. In this study, we decided to tackle the study of the endometrial microbiota through analysis of bacterial population in women subjected to elective caesarean delivery. As a pilot study, a cohort of 19 Caucasian women at full term of normal pregnancy and with a prospection of elective caesarean delivery was enrolled for endometrium sampling at the time of caesarean section. Sampling was carried out by endometrial biopsy soon after the delivery of the newborn and the discharge of the placenta and fetal membranes from the uterus. Bacterial composition was established by a deep metabarcoding next generation sequencing (NGS) procedure addressing the V5–V6 hypervariable region of the 16S rRNA gene. Amplicon sequences were analysed by bioinformatic procedures for denoising and taxonomic classification. The RDP database was used as 16S rRNA reference collection. Metabarcoding analysis showed the presence of a common bacterial composition, including six genera classifiable within the human microbiota (Cutibacterium, Escherichia, Staphylococcus, Acinetobacter, Streptococcus, Corynebacterium), that could be part of the core endometrial microbiota under the specific conditions examined. These results can provide useful information for future studies on the correlations between bacteria and successful pregnancies.

Accurate quantification of bacterial abundance in metagenomic DNAs accounting for variable DNA integrity levels

“…ddPCR (Bio-Rad, Hercules, CA, USA) was performed to determine the total number of 16S copies by using universal primers targeting the V5–V6 regions of 16S rDNA [31], as they have been used successfully in other DNA metabarcoding analyses (primer sequences: forward, B-V5 : 5′-ATTAGATACCCYGGTAGTCC-3′; reverse, A-V6, 5′-ACGAGCTGACGACARCCATG-3′) [32, 33]. For the quantification of the gene copy numbers for Akkermansia muciniphila 16S rRNA, specific primers targeting the V7–V8 regions were used (primer sequence: forward, AM1 : 5′-CAGCACGTGAAGGTGGGGAC-3′; reverse, AM2 : 5′-CCTTGCGGTTGGCTTCAGAT-3′) [34].…”

New Opportunities for Endometrial Health by Modifying Uterine Microbial Composition: Present or Future?

“…Several studies demonstrated that asymptomatic women harbour commensal microbial communities in their uterus [8,11,16,22,102], and that the uterine microbiome seems to be altered in women who suffer gynaecological pathologies such CE [14][15][16], endometriosis [17,19,20], dysfunctional endometrial bleeding [22], endometrial polyps [16], endometrial cancer or hyperplasia [16,[23][24][25], and infertility [4,8,11,13] (Table 1). All these studies support the evidence that the uterine microbial composition is clinically relevant and requires further investigation.…”

“…Acinetobacter [102,103], Bacillus [103], Barnesiella [23], Bifidobacterium [11], Blautia [23], Corynebacterium [102], Desulfosporosinus [16], Enterobacter [16], Escherichia [102,103], Fusobacterium [22], Gardnerella [11], Jonquetella [22], Lactobacillus [8,11,16,19], Parabacteroides [23], Prevotella [11,22], Propionibacterium [102], Pseudomonas [16], Ralstonia [16], Shigella [23], Staphylococcus [23,102], Streptococcus [11,102] Infertility…”

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

“…In contrast, it was detected in only 1/22 (4.5%) background technical controls. Acinetobacter has been reported in prior sequence-based investigations of the human endometrium (20, 23, 24, 29, 30), and it has been cultured from the human endometrium as well (95). The primary ASV classified as Ottawia was detected in 6/10 (60%) uterine wall samples at an average relative abundance of 10.5%.…”