Evidence that the endometrial microbiota has an effect on implantation success or failure.

Bacterial cells in the human body account for 1-3% of total body weight and are at least equal in number to human cells. Recent research has focused on understanding how the different bacterial communities in the body (eg, gut, respiratory, skin, and vaginal microbiomes) predispose to health and disease. The microbiota of the reproductive tract has been inferred from the vaginal bacterial communities, and the uterus has been classically considered a sterile cavity. However, while the vaginal microbiota has been investigated in depth, there is a paucity of consistent data regarding the existence of an endometrial microbiota and its possible impact in reproductive function. This study sought to test the existence of an endometrial microbiota that differs from that in the vagina, assess its hormonal regulation, and analyze the impact of the endometrial microbial community on reproductive outcome in infertile patients undergoing in vitro fertilization. To identify the existence of an endometrial microbiota, paired samples of endometrial fluid and vaginal aspirates were obtained simultaneously from 13 fertile women in prereceptive and receptive phases within the same menstrual cycle (total samples analyzed n = 52). To investigate the hormonal regulation of the endometrial microbiota during the acquisition of endometrial receptivity, endometrial fluid was collected at prereceptive and receptive phases within the same cycle from 22 fertile women (n = 44). Finally, the reproductive impact of an altered endometrial microbiota in endometrial fluid was assessed by implantation, ongoing pregnancy, and live birth rates in 35 infertile patients undergoing in vitro fertilization (total samples n = 41) with a receptive endometrium diagnosed using the endometrial receptivity array. Genomic DNA was obtained either from endometrial fluid or vaginal aspirate and sequenced by 454 pyrosequencing of the V3-V5 region of the 16S ribosomal RNA (rRNA) gene; the resulting sequences were taxonomically assigned using QIIME. Data analysis was performed using R packages. The χ2 test, Student t test, and analysis of variance were used for statistical analyses. When bacterial communities from paired endometrial fluid and vaginal aspirate samples within the same subjects were interrogated, different bacterial communities were detected between the uterine cavity and the vagina of some subjects. Based on its composition, the microbiota in the endometrial fluid, comprising up to 191 operational taxonomic units, was defined as a Lactobacillus-dominated microbiota (>90% Lactobacillus spp.) or a non-Lactobacillus-dominated microbiota (<90% Lactobacillus spp. with >10% of other bacteria). Although the endometrial microbiota was not hormonally regulated during the acquisition of endometrial receptivity, the presence of a non-Lactobacillus-dominated microbiota in a receptive endometrium was associated with significant decreases in implantation [60.7% vs 23.1% (P = .02)], pregnancy [70.6% vs 33.3% (P = .03)], ongoing pregnancy [58.8% vs 13.3% (P = .02)], and live birth [58.8% vs 6.7% (P = .002)] rates. Our results demonstrate the existence of an endometrial microbiota that is highly stable during the acquisition of endometrial receptivity. However, pathological modification of its profile is associated with poor reproductive outcomes for in vitro fertilization patients. This finding adds a novel microbiological dimension to the reproductive process.

Moreno I ，Codoñer FM ，Vilella F ，Valbuena D ，Martinez-Blanch JF ，Jimenez-Almazán J ，Alonso R ，Alamá P ，Remohí J ，Pellicer A ，Ramon D ，Simon C ... -  《-》

Colonization of the upper genital tract by vaginal bacterial species in nonpregnant women.

The objective of the study was to evaluate the upper genital tract (UGT) presence of vaginal bacterial species using sensitive molecular methods capable of detecting fastidious bacterial vaginosis (BV)-associated bacteria. Vaginal swabs were collected prior to hysterectomy. The excised uterus was sterilely opened and swabs collected from the endometrium and upper endocervix. DNA was tested in 11 quantitative polymerase chain reaction (PCR) assays for 12 bacterial species: Lactobacillus iners, L crispatus, L jensenii, Gardnerella vaginalis, Atopobium vaginae, Megasphaera spp, Prevotella spp, Leptotrichia/Sneathia, BVAB1, BVAB2, BVAB3, and a broad-range16S ribosomal ribonucleic acid gene assay. Endometrial fluid was tested with Luminex and an enzyme-linked immunosorbent assay for cytokines and defensins and tissue for gene expression of defensins and cathelicidin. We enrolled 58 women: mean aged 43±7 years, mostly white (n=46; 79%) and BV negative (n=43; 74%). By species-specific quantitative PCR, 55 (95%) had UGT colonization with at least 1 species (n=52) or were positive by 16S PCR (n=3). The most common species were L iners (45% UGT, 61% vagina), Prevotella spp (33% UGT, 76% vagina) and L crispatus (33% UGT, 56% vagina). Median quantities of bacteria in the UGT were lower than vaginal levels by 2-4 log10 ribosomal ribonucleic acid gene copies per swab. There were no differences in the endometrial inflammatory markers between women with no bacteria, Lactobacillus only, or any BV-associated species in the UGT. Our data suggest that the endometrial cavity is not sterile in most women undergoing hysterectomy and that the presence of low levels of bacteria in the uterus is not associated with significant inflammation.

Mitchell CM ，Haick A ，Nkwopara E ，Garcia R ，Rendi M ，Agnew K ，Fredricks DN ，Eschenbach D ... -  《-》

Controlled ovarian stimulation and progesterone supplementation affect vaginal and endometrial microbiota in IVF cycles: a pilot study.

Carosso A ，Revelli A ，Gennarelli G ，Canosa S ，Cosma S ，Borella F ，Tancredi A ，Paschero C ，Boatti L ，Zanotto E ，Sidoti F ，Bottino P ，Costa C ，Cavallo R ，Benedetto C ... -  《-》

The vaginal microbiota composition of women undergoing assisted reproduction: a prospective cohort study.

To evaluate the impact of vaginal microbiota on pregnancy outcomes in women undergoing assisted reproduction. A prospective cohort study. A university-based assisted reproductive technology (ART) centre. 223 women undergoing ART treatment. Prior to embryo transfer, vaginal samples were collected from the posterior fornix. Vaginal microbiota identification was carried out using next-generation sequencing and categorised according to the V3-V4 hypervariable region in the 16S rRNA gene region. ART clinical outcomes (implantation, clinical pregnancy rates and live birth rates). The live birth rate in women with community state type (CST)-I (39%) was higher than that in women with CST-III (21.5%) but the difference was not statistically significant (P = 0.052). The relative abundance of Lactobacillus was lower in women who failed to become pregnant (NP group) (67.71%) than in women who became pregnant (PR group) (79.72%). However, this difference was not statistically significant (P = 0.06). In the NP group, the relative abundance of Streptococcus (7.81%) and Gardnerella (9.40%) was higher than that in the PR group (relative abundance of Streptococcus and Gardnerella was 2.28% and 5.56%, respectively). The abundance of Streptococcus was found to be statistically significantly different between the two study groups (P = 0.014). Linear discriminant analysis (LDA) further validated that Streptococcus had the highest contribution (LDA score >4.0) to the difference between these two groups. Streptococcus has the highest contribution to the distinction between the PR and NP groups. A relatively high abundance of Streptococcus in the vaginal microbiota may be associated with a lower ART success rate.

Karaer A ，Doğan B ，Günal S ，Tuncay G ，Arda Düz S ，Ünver T ，Tecellioğlu N ... -  《-》

Vaginal and endometrial microbiome dysbiosis associated with adverse embryo transfer outcomes.

Assisted reproductive technology (ART) is the most effective method to treat infertility and the pathogenesis of implantation failure after in vitro fertilization-embryo transfer (IVF-ET) is a challenging filed in infertility. Microbes in the female reproductive tract are considered to be associated with gynecological and obstetric diseases. However, its effects on embryo implantation failure are unsured. This study aimed to investigate reproductive tract dysbiosis, identify different bacteria in reproductive tract as potential biomarkers of embryo implantation failure and demonstrate the pathogenesis through metabolites analysis. We compared the data from 16S rRNA gene and metagenome in reproductive tracts through QIIME2 and HUMAnN2 by the times of embryo implantation failure on 239 infertile patients and 17 healthy women. Our study revealed a strong positive correlation between Lactobacillus abundance and embryo implantation success (IS) after IVF-ET. The microbial community composition and structure in reproductive tract showed substantially difference between the embryo implantation failure (IF) and healthy control. Moreover, we established a diagnostic model through receiver operating characteristic (ROC) with 0.913 area under curve (AUC) in IS and multiple implantation failures (MIF), verified its effectiveness with an AUC = 0.784 demonstrating microbial community alterations could efficiently discriminate MIF patients. Metagenome functional analyses of vaginal samples from another independent infertile patients after IVF-ET revealed the L-lysine synthesis pathway enriched in IF patients, along with ascended vaginal pH and decreased Lactobacillus abundance. This study clarifies several independent relationships of bacteria in vagina and endometrial fluid on embryo implantation failure and undoubtedly broadens the understanding about female reproductive health.

Su W ，Gong C ，Zhong H ，Yang H ，Chen Y ，Wu X ，Jin J ，Xi H ，Zhao J ... -  《Reproductive Biology and Endocrinology》