Systematic Comparison of Bacterial Colonization of Endometrial Tissue and Fluid Samples in Recurrent Miscarriage Patients: Implications for Future Endometrial Microbiome Studies

Abstract

BACKGROUND A recent study has reported that the microbiota in endometrial fluid of patients receiving in vitro fertilization and embryo transfer (IVF-ET) may predict implantation and pregnancy rates. However, studies are lacking that simultaneously compare the microbiota between endometrial fluid and tissue samples. Whether the microbiota composition in endometrial fluid reflects that in the endometrial tissue remains unclear. METHODS We systematically profiled the microbiota in endometrial fluid and tissue samples of IVF-ET patients using massively parallel sequencing. The bacterial 16S ribosomal RNA gene (V4 region) was PCR-amplified. Sequencing reads with >98% nucleotide identity were clustered as a bacterial taxon. To account for the different number of reads per sample, we normalized the read counts of each taxon before comparing its relative abundances across samples. RESULTS Thirteen taxa, including Verrucomicrobiaceae, Brevundimonas, Achromobacter, Exiguobacterium, and Flavobacterium, were consistently detected only in endometrial tissue samples but not fluid samples. Eight taxa were detected in fluid but not tissue. Twenty-two taxa were differentially abundant between fluid and tissue samples (adjusted P values, 4.1 × 10−25 to 0.025). The numbers of taxa identified per 1000 sequencing reads, diversity, and evenness in fluid samples were smaller than those in tissue samples. CONCLUSIONS Our data suggest that the microbiota composition in endometrial fluid does not fully reflect that in endometrial tissue. Sampling from both endometrial fluid and biopsy allows a more comprehensive view of microbial colonization. Further efforts are needed to identify the preanalytical effects, including sampling sites, methods, and sequencing depth, on profiling endometrial microbiota.

Differential Secretion of Inflammatory Cytokines by Human Trophoblasts in the Presence of <b><i>Escherichia coli</i></b>, <b><i>Lactobacillus crispatus</i></b>, and <b><i>Lactobacillus jensenii</i></b>

“…Another report, using human ectocervical and endocervical cell lines treated with soluble products produced by L. crispatus induced responses that may result in cervical epithelial barrier protection, including secretion of IL-10 -the same response we found in our experiments with trophoblasts, and that can be interpreted as being conducive to immunomodulation [64]. Recent evidence in non-pregnant women suggests that the endometrial cavity may have a characteristic microbiota with low biomass [65][66][67][68][69][70][71][72][73][74][75][76][77]. We do not have information about the intrauterine microbiota during pregnancy, but placental infections may result from hematogenously disseminated microorganisms, or more commonly, from microorganisms ascending from the lower genital tract [78][79][80][81].…”

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

“…In that study, Lactobacillus dominance (>90% of all bacteria) correlated positively with embryo implantation, pregnancy and live birth rates among infertile women undergoing in vitro fertilisation (IVF) [11]. Other studies have not detected any significant associations between endometrial microbiome and the treatment outcomes [4,[6][7][8][9][10]12,13].…”

“…Atopobium [6,[8][9][10], Bacteroides [12], Betaproteobacteria [12], Bifidobacterium [5,[8][9][10][11]13,104], Burkholderia [7], Chitinophagaceae [12], Corynebacterium [104], Escherichia/Shigella [10,12], Flavobacterium [4], Gardnerella [5][6][7][8][9][10][11]13], Lactobacillus [4][5][6][7][8][9][10][11]13,104], Megasphaera [9,10], Pelomonas [12], Prevotella [8][9][10][11]13], Pseudoalteromonas [5], Rhodanobacter [5], Sneathia [8,9], Staphylococcus [8]…”

“…The initial studies of endometrial microbiome suggest its association with reproductive outcomes in assisted reproduction [4][5][6][7][8][9][10][11][12][13] and with different gynaecological pathologies such as chronic endometritis (CE) [14][15][16], endometriosis [13,[17][18][19][20][21], dysfunctional endometrial bleeding [22], endometrial polyps [16], and endometrial cancer or hyperplasia [23][24][25]. Nevertheless, causality has been difficult to prove because the reproductive tract represents a polymicrobial niche [26], and it is not clear whether dysbiosis within the uterus is a cause or a consequence of a pathology.…”

Structural Variations of Vaginal and Endometrial Microbiota: Hints on Female Infertility

“…The technique we used to obtain endometrial material is the biopsy of the tissue. This material is more representative of the uterine cavity microbiota (Fang et al, 2016 ; Verstraelen et al, 2016 ; Chen et al, 2017 ; Miles et al, 2017 ; Liu et al, 2018 ) in comparison with the other studies that used only uterine fluid extracted by endometrial swab or embryo-transfer catheter tip analysis (Franasiak et al, 2016 ; Khan et al, 2016 ; Moreno et al, 2016 ; Tao et al, 2017 ; Kyono et al, 2018 , 2019 ; Pelzer et al, 2018 ).…”