Objective: To systematically compare the endometrial microbiota in infertile women with and without chronic endometritis (CE), as diagnosed by a quantitative and reference range-based method. Design: Case-control observational study. Setting: University-affiliated hospital. Patient(s): One hundred and thirty infertile women. Intervention(s): Endometrial biopsy and fluid (uterine lavage, UL) collected precisely 7 days after LH surge, with plasma cell density (PCD) determined based on Syndecan-1 (CD138)-positive cells in the entire biopsy section and culture-independent massively parallel sequencing of the 16S ribosomal RNA gene performed on both the CE and non-CE endometrial fluid samples. Main Outcome Measure(s): Relative abundance of bacterial taxa. Result(s): Chronic endometritis was diagnosed if the PCD was above the 95th percentile (>5.15 cells per 10 mm 2 ) of the reference range in fertile control subjects. With this stringent diagnostic criterion, 12 women (9%) were diagnosed with CE. Sequencing was successfully performed on all endometrial samples obtained by UL) (CE, n ¼ 12; non-CE, n ¼ 118). The median relative abundance of Lactobacillus was 1.89% and 80.7% in the CE and non-CE microbiotas, respectively. Lactobacillus crispatus was less abundant in the CE microbiota (fold-change, range: 2.10-2.30). Eighteen non-Lactobacillus taxa including Dialister, Bifidobacterium, Prevotella, Gardnerella, and Anaerococcus were more abundant in the CE microbiota (fold-change, 2.10-18.9). Of these, Anaerococcus and Gardnerella were negatively correlated in relative abundance with Lactobacillus (SparCC correlation magnitude, range: 0.142-0.177). Conclusion(s): Chronic endometritis was associated with a statistically significantly higher abundance of 18 bacterial taxa in the endometrial cavity.

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.

(Abstracted from Fertil Steril 2019;112:707–717) Chronic endometriosis (CE), a state of chronic inflammation in the endometrial lining, has been associated with reproductive failure and is diagnosed based on the presence of CD138+ plasma cells. There is wide variance in CE among infertile women (ranging from 2.8% to 57%) and a lack of consensus on the diagnostic criteria.

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