O-259 1.\tComparison of endometrial versus vaginal microbiota in 71 infertile patients
Authors: Finzer P , Polifke A , Von Schwedler A , Gulba R , Nassar N N R 
Published: June 2023

Abstract

Study question
1.Mostly, endometrial microbiome probes are acquired by trans-cervical sampling using a “pipelle”. However, it is unclear, whether this approach “contaminates” the endometrial material.

Summary answer
1.Vaginal and endometrial microbiome samples are significantly different from each other with respect to (alpha-)diversity showing the endometrial community to be more polymicrobial.

What is known already
1. The female genital tract is colonized by a continuum of microbiota, ranging from the typically more diverse, but lower-biomass, bacterial communities in the endometrium to the typically less diverse, but higher-biomass, communities in the vagina (Chen et al., 2017). In reproductive-age women, vaginal bacterial communities are mainly dominated by lactobacilli (Ravel, 2011). By contrast, the composition of the endometrial microbiome has remained less well-characterized. With the more recent introduction of next generation sequencing a more quantitative and comprehensive picture of the composition of endometrial bacterial communities has begun to emerge (Baker et al., 2018).

Study design, size, duration
1. The study was conducted at “novum, Zentrum für Reproduktionsmedizin”, Essen / Duisburg, Germany. Of 76 enrolled patients undergoing treatment,73 provided both vaginal swab and endometrial biopsy samples from the same sequencing run between February 2020 and March 2021. All analyses were carried out retrospectively. Information about pregnancy or delivery were extracted from medical records or obtained by telephone or email interviews conducted through June 2022.

Participants/materials, setting, methods
1.Amplification of V1-V2 16S rDNA regions was carried out at “dus.ana, Düsseldorf Analytik”, Germany, using the QIAseq 16S screening and regional panels. CLC Microbial Genomic Workbench was used to assess bacterial community composition, alpha diversity, and microbial community structure (PCoA). Pairs of complete corresponding vaginal and endometrial microbiota data were available for 71 patients (two patient was excluded due to too low read counts in the vaginal or the endometrial probe, respectively).

Main results and the role of chance
1.Patients exhibiting a mean age of 35 years (range 26 – 42) and a mean body mass index (BMI) of 24,5 (range 18,8 to 38,7). 20 (28,2 %) patients were diagnosed with chronic endometritis (more than 1 plasmacyte per HPF) and 15 (21,1 %) with endometriosis. 40 study participants were found to have undergone past miscarriages, and 11 study participants were found to have given birth to 15 children.
2.Abundance analyses showed differences between vaginal and endometrial samples for the Lactobacillus sp., most pronounced for L. jensenii and L. gasserie. The group of non-lactobacilli was only slightly enlarged in the endometrial group, encompassing mainly G. vaginalis. With regard to diversity (Shannon entropy), both microbiota are significantly different (Kruskal-Wallis test). In addition, distribution of the genital microbial communities illustrated by PCoA indicated that the vaginal samples were clustered together showing variance only in one dimension. However, the endometrial samples were far away from each other and grouped very disperse.

Limitations, reasons for caution
1.Group of infertile patients of an IVF center with different underlying clinical diagnosis studied in a retrospective setting.

Wider implications of the findings
1.Trans-cervical sampling with a “pipelle” provides an endometrial microbiome which is obviously a more polymicrobial community - with a higher diversity, that may harbor more biological heterogeneity, and hence functionality – than the corresponding vaginal microbiome. Further analyses studying the correlation between sequencing and clinical data are ongoing.

Trial registration number
2021-1448