How uterine microbiota might be responsible for a receptive, fertile endometrium

Approaches to Improve Endometrial Receptivity in Case of Repeated Implantation Failures

Repeated implantation failures are a constant challenge in reproductive medicine with a significant impact both on health providers and on infertile couples. Several approaches have been proposed so far as effective; however, accumulative data have clarified that most of the treatment options do not have the evidence base for a generalized application to be suggested by the relevant societies. Implantation failures are attributed to either poor quality embryos or to defected endometrial receptivity. The current review aims to summarize in a systematic way all the new trends in managing RIF via interference with endometrial receptivity. The authors focus mainly, but not exclusively, on endometrial injury prior to embryo transfer and endometrial priming with autologous cells or biological agents. To this direction, a systematic search of the Pubmed database has been conducted taking into account the emerged evidence of the last two decades. All the suggested interventions are herein presented and analyzed in terms of reproductive outcomes. It is evident that properly powered and designed randomized trials are needed to support a new standard approach in RIF treatment that will safely be incorporated in national and international guidelines.

Gut and Reproductive Tract Microbiota Adaptation during Pregnancy: New Insights for Pregnancy-Related Complications and Therapy

Pregnancy is characterized by maternal adaptations that are necessary to create a welcoming and hospitable environment for the fetus. Studies have highlighted how the microbiota modulates several networks in humans through complex molecular interactions and how dysbiosis (defined as quantitative and qualitative alterations of the microbiota communities) is related to human pathologies including gynecological diseases. This review analyzed how maternal uterine, vaginal, and gut microbiomes could impact on fetus health during the gestational period. We evaluated the role of a dysbiotic microbiota in preterm birth, chorioamnionitis, gestational diabetes mellitus and pre-eclampsia. For many years it has been hypothesized that newborns were sterile organisms but in the past few years this paradigm has been questioned through the demonstration of the presence of microbes in the placenta and meconium. In the future, we should go deeper into the concept of in utero colonization to better understand the role of microbiota through the phases of pregnancy. Numerous studies in the literature have already showed interesting results regarding the role of microbiota in pregnancy. This evidence gives us the hope that microbiota modulation could be a novel strategy to reduce the morbidity and mortality related to pregnancy complications in the future.

Impact of chronic endometritis in infertility: a SWOT analysis

Chronic endometritis is a pathology often associated with reproductive failure, but there are still no clear recommendations on whether its inclusion in the initial study of infertile couples is necessary. In this discussion paper, based on a SWOT (Strengths, Weaknesses, Opportunities, Threats) analysis, the different aspects of the repercussions of chronic endometritis in fertility are evaluated. To avoid possible subjectivity in the analysis and results of this study, the researchers followed the Oxford criteria for the evaluation of evidence. The results from the evaluation of the reviewed literature seem to indicate that, pending new evidence, it would be advisable not to include chronic endometritis in the initial baseline study before assisted reproduction in order not to delay other assisted reproduction treatments. However, it would be advisable in cases of repetitive implantation failure and pregnancy loss after having undergone IVF with viable embryos and before continuing with costly reproductive processes, since results could be improved. The development of randomized studies assessing the impact of antibiotic treatment as a possible therapeutic option in infertile women with chronic endometritis, as well as the possible impact on endometrial microbiota and receptivity/implantation, would allow for the establishment of more precise clinical guidelines in this regard.

Peptidoglycan Switches Off the TLR2-Mediated Sperm Recognition and Triggers Sperm Localization in the Bovine Endometrium

In mammals, the uterine mucosal immune system simultaneously recognizes and reacts to most bacteria as well as allogenic sperm mainly through the Toll-like receptors (TLR)2/4 signaling pathway. Here, we characterized the impact of pathogen-derived TLR2/4 ligands (peptidoglycan (PGN)/lipopolysaccharide (LPS)) on the immune crosstalk of sperm with the bovine endometrial epithelium. The real-time PCR analysis showed that the presence of low levels of PGN, but not LPS, blocked the sperm-induced inflammatory responses in bovine endometrial epithelial cells (BEECs) in vitro. Immunoblotting analysis revealed that PGN prevented the sperm-induced phosphorylation of JNK in BEECs. Activation or blockade of the TLR2 system in the endometrial epithelium verified that TLR2 signaling acts as a commonly-shared pathway for PGN and sperm recognition. The impairment of endometrial sperm recognition, induced by PGN, subsequently inhibited sperm phagocytosis by polymorphonuclear neutrophils (PMNs). Moreover, using an ex vivo endometrial explant that more closely resembles those in vivo conditions, showed that sperm provoked a mild and reversible endometrial tissue injury and triggered PMN recruitment into uterine glands, while PGN inhibited these events. Of note, PGN markedly increased the sperm attachment to uterine glands, and relatively so in the surface epithelium. However, addition of the anti-CD44 antibody into a PGN-sperm-explant co-culture completely blocked sperm attachment into glands and surface epithelia, indicating that the CD44 adhesion molecule is involved in the PGN-triggered sperm attachment to the endometrial epithelium. Together, these findings demonstrate that, the presence of PGN residues disrupts sperm immune recognition and prevents the physiological inflammation induced by sperm in the endometrial epithelium via the MyD88-dependent pathway of TLR2 signaling, possibly leading to impairment of uterine clearance and subsequent embryo receptivity.

Analysing endometrial microbiome: methodological considerations and recommendations for good practice

There is growing evidence that the upper female genital tract is not sterile, harbouring its own microbial communities. However, the significance and the potential effect of endometrial microorganisms on reproductive functions remain to be fully elucidated. Analysing the endometrial microbiome, the microbes and their genetic material present in the endometrium, is an emerging area of study. The initial studies suggest it is associated with poor reproductive outcomes and with different gynaecological pathologies. Nevertheless, studying a low-biomass microbial niche as is endometrium, the challenge is to conduct well-designed and well-controlled experiments in order to avoid and adjust for the risk of contamination, especially from the lower genital tract. Herein, we aim to highlight methodological considerations and propose good practice recommendations for future endometrial microbiome studies.

The Interaction Between Microorganisms, Metabolites, and Immune System in the Female Genital Tract Microenvironment

The female reproductive tract microenvironment includes microorganisms, metabolites, and immune components, and the balance of the interactions among them plays an important role in maintaining female reproductive tract homeostasis and health. When any one of the reproductive tract microorganisms, metabolites, or immunity is out of balance, it will affect the other two, leading to the occurrence and development of diseases and the appearance of corresponding symptoms and signs, such as infertility, miscarriage, premature delivery, and gynecological tumors caused by infectious diseases of the reproductive tract. Nutrients in the female reproductive tract provide symbiotic and pathogenic microorganisms with a source of nutrients for their own reproduction and utilization. At the same time, this interaction with the host forms a variety of metabolites. Changes in metabolites in the host reproductive tract are related not only to the interaction between the host and microbiota under dysbiosis but also to changes in host immunity or the environment, all of which will participate in the pathogenesis of diseases and lead to disease-related phenotypes. Microorganisms and their metabolites can also interact with host immunity, activate host immunity, and change the host immune status and are closely related to persistent genital pathogen infections, aggravation of infectious diseases, severe pregnancy outcomes, and even gynecological cancers. Therefore, studying the interaction between microorganisms, metabolites, and immunity in the reproductive tract cannot only reveal the pathogenic mechanisms that lead to inflammation of the reproductive tract, adverse pregnancy outcomes and tumorigenesis but also provide a basis for further research on the diagnosis and treatment of targets.

Microbiome affecting reproductive outcome in ARTs

Current scientific evidence reveals the importance of the human microbiome in health and disease. The presence of microbiota within the male and female reproductive tract has been well-documented and present theories imply that a possible disruption of their concentrations may have adverse effects on reproductive health and reproductive outcomes. Altered endometrial and vaginal microbiome could potential affect the reproductive outcome in infertile couples undergoing assisted reproductive techniques. Analysis of seminal fluids could also facilitate a prompt and appropriate approach in cases of abnormal male reproductive microflora. Essential knowledge on this subject could provide fertility experts better understanding with regards to unexplained fertility, increasing the success rates of ARTs. In this review, we summarise the current knowledge on the microbiota of the male and female reproductive tract and its impact on the success rates of ARTs in infertile couples.

Skp2 Deteriorates the Uterine Receptivity by Interacting with HOXA10 and Promoting its Degradation

Receptive endometrium plays a core role in successful embryo implantation, and about one-third of repeated embryo implantation failures are attributed to endometrial receptive defects. S-phase kinase-associated protein 2 (SKP2), a member of the F-box protein family, plays an important role in many cellular processes, including cell proliferation and apoptosis. However, its role in endometrial receptivity is still unclear. Here, we identified SKP2 was obviously upregulated in the patients with infertility. Functional study showed that SKP2 overexpression inhibited endometrial epithelial cell (EEC) proliferation, whereas SKP2 knockdown promoted the proliferation of EECs. In addition, the overexpression of SKP2 also repressed adhesion rate of embryonic cells to EECs. In vivo studies further suggested that the upregulation of SKP2 obviously suppressed endometrium receptivity formation and embryo implantation potential. Mechanistical study clarified that SKP2 directly interacted with HOXA10 and decreased protein stability through promoting the ubiquitin-mediated proteasome degradation of HOXA10. In conclusion, the current study documented that the high expression of SKP2 deteriorates endometrial receptivity formation by decreasing the HOXA10 expression and suggested that SKP2 may be defined as a marker of endometrial receptivity, and as a target for the diagnosis and treatment of infertility.

The development of the human uterus: morphogenesis to menarche

There is emerging evidence that early uterine development in humans is an important determinant of conditions such as ontogenetic progesterone resistance, menstrual preconditioning, defective deep placentation and pre-eclampsia in young adolescents. A key observation is the relative infrequency of neonatal uterine bleeding and hormone withdrawal at birth. The origin of the uterus from the fusion of the two paramesonephric, or Müllerian, ducts was described almost 200 years ago. The uterus forms around the 10th week of foetal life. The uterine corpus and the cervix react differently to the circulating steroid hormones during pregnancy. Adult uterine proportions are not attained until after puberty. It is unclear if the endometrial microbiome and immune response-which are areas of growing interest in the adult-play a role in the early stages of uterine development. The aim is to review the phases of uterine development up until the onset of puberty in order to trace the origin of abnormal development and to assess current knowledge for features that may be linked to conditions encountered later in life. The narrative review incorporates literature searches of Medline, PubMed and Scopus using the broad terms individually and then in combination: uterus, development, anatomy, microscopy, embryology, foetus, (pre)-puberty, menarche, microbiome and immune cells. Identified articles were assessed manually for relevance, any linked articles and historical textbooks. We included some animal studies of molecular mechanisms. There are competing theories about the contributions of the Müllerian and Wolffian ducts to the developing uterus. Endometrium features are suggestive of an oestrogen effect at 16-20 weeks gestation. The discrepancy in the reported expression of oestrogen receptor is likely to be related to the higher sensitivity of more recent techniques. Primitive endometrial glands appear around 20 weeks. Features of progestogen action are expressed late in the third trimester. Interestingly, progesterone receptor expression is higher at mid-gestation than at birth when features of endometrial maturation are rare. Neonatal uterine bleeding occurs in around 5% of neonates. Myometrial differentiation progresses from the mesenchyme surrounding the endometrium at the level of the cervix. During infancy, the uterus and endometrium remain inactive. The beginning of uterine growth precedes the onset of puberty and continues for several years after menarche. Uterine anomalies may result from fusion defects or atresia of one or both Müllerian ducts. Organogenetic differentiation of Müllerian epithelium to form the endometrial and endocervical epithelium may be independent of circulating steroids. A number of genes have been identified that are involved in endometrial and myometrial differentiation although gene mutations have not been demonstrated to be common in cases of uterine malformation. The role, if any, of the microbiome in relation to uterine development remains speculative. Modern molecular techniques applied to rodent models have enhanced our understanding of uterine molecular mechanisms and their interactions. However, little is known about functional correlates or features with relevance to adult onset of uterine disease in humans. Prepubertal growth and development lends itself to non-invasive diagnostics such as ultrasound and MRI. Increased awareness of the occurrence of neonatal uterine bleeding and of the potential impact on adult onset disease may stimulate renewed research in this area.

Impaired pathogen-induced autophagy and increased IL-1β and TNFα release in response to pathogenic triggers in secretory phase endometrial stromal cells of endometriosis patients

RESEARCH QUESTION

It is not clear whether innate immunity along with autophagy is altered in endometrial cells of patients with endometriosis.

DESIGN

This study evaluated the effects of lipopolysaccharide (LPS) or polyinosinic:polycytidylic acid (poly I:C) stimulation on autophagy induction, pro-IL-1β expression, and secretion of interleukin-1β (IL-1β) and tumour necrosis factor-α (TNFα) in endometrial epithelial and/or stromal cells of patients with endometriosis (EE-endo, ES-endo, respectively), those of patients with hydrosalpinx (EE-hydro, ES-hydro, respectively) and those of healthy fertile women (EE-healthy, ES-healthy, respectively), with and without inhibition of autophagy by autophagy-related (ATG)13 gene small interfering RNA (siRNA).

RESULTS

Stimulation with either LPS or poly I:C triggered autophagy in EE/ES-healthy, whereas no significant induction was observed in either EE/ES-endo or EE/ES-hydro. In EE- and/or ES-healthy, IL-1β and/or TNFα secretion after stimulation with LPS or poly I:C was significantly higher in cells with ATG13 knockdown compared with those with siRNA control (P < 0.03), whereas no significant difference was observed in either EE/ES-endo or EE/ES-hydro. In the secretory phase ES-endo without autophagy inhibition, IL-1β and TNFα secretion were significantly higher compared with those of ES-healthy after stimulation with either LPS or poly I:C for 4 h (P < 0.001) and for 24 h (P < 0.01).

CONCLUSION

Pathogen-induced autophagy was impaired in EE/ES-endo. Increased IL-1β and TNFα release in response to pathogenic triggers in the secretory phase ES-endo may result in the development of an inflammatory uterine microenvironment detrimental to successful embryo implantation.

Comparative Analysis of Lower Genital Tract Microbiome Between PCOS and Healthy Women

Women with polycystic ovarian syndrome (PCOS) often have a history of infertility and poor pregnancy outcome. The character of the lower genital tract (LGT) microbiome of these patients is still unknown. We collected both vaginal and cervical canal swabs from 47 PCOS patients (diagnosed by the Rotterdam Criteria) and 50 healthy reproductive-aged controls in this study. Variable regions 3–4 (V3–4) were sequenced and analyzed. Operational taxonomic unit (OTU) abundance was noted for all samples. Taxa that discriminated between PCOS and healthy women was calculated by linear discriminant analysis effect size (LEFSe). Results from 97 paired vaginal and cervical canal samples collected from 97 women [mean age 30 (±4 years)] were available for analysis. Using the Rotterdam Criteria, 47 women were diagnosed with PCOS (PCOS, n = 47; control, n = 50). There was no significant difference between cervical canal microbiome and vaginal microbiome from the same individual, however, Lactobacillus spp. was less abundant in both vaginal and cervical canal microbiome of PCOS patients. Several non-Lactobacillus taxa including Gardnerella_vaginalis_00703mash, Prevotella_9_other, and Mycoplasma hominis, were more abundant in the LGT microbiota of PCOS patients. There is a difference between the microorganism in the LGT of patients with PCOS and healthy reproductive-aged women.

Uterine microbiome-low biomass and high expectations†

The existence of different bacterial communities throughout the female reproductive tract has challenged the traditional view of human fetal development as a sterile event. There is still no consensus on what physiological microbiota exists in the upper reproductive tract of the vast majority of women who are not in periods of infection or pregnancy, and the role of bacteria that colonize the upper reproductive tract in uterine diseases or pregnancy outcomes is not well established. Despite published studies and advances in uterine microbiome sequencing, some study aspects-such as study design, sampling method, DNA extraction, sequencing methods, downstream analysis, and assignment of taxa-have not yet been improved and standardized. It is time to further investigate the uterine microbiome to increase our understanding of the female reproductive tract and to develop more personalized reproductive therapies, highlighting the potential importance of using microbiological assessment in infertile patients.

[Ten questions about bacterial vaginosis]

The physiopathology of bacterial vaginosis (BV), the ultimate stage of vaginal dysbiosis, has benefited from recent advances in molecular biology, highlighting, among others, the important role of A. vaginae. Certain immunological specificities (variants of TLR4, elevation of IL-1β, for example) explain the variations in the prevalence of this infection, the poor clinical and cellular inflammatory response and the promoting influence of BV on the acquisition and progression of some sexually transmitted infections. These advances do not fully elucidate the causes of the high rate of recurrences. Some risk factors for relapses of BV have been identified such as tobacco use, stress or hygienic errors have been associated to relapses of BV. However, other paths are beginning to be explored such as the role of sexual transmission, the resistance of certain bacteria associated to BV to nitroimidazoles or the lack of efficacy of conventional treatments on dysbiosis itself. Taking into acount this vaginal dysbiosis appears to be important or even essential to better control the natural history of HPV-hr infection or improve the success rate of IVF, for example. Despite heterogeneous results, the use of probiotics as a complement to conventional treatments (nitroimidazoles, dequalinium chloride) has demonstrated a preventive effect on BV recurrences. Further studies are needed to customize the contribution of probiotics (or synbiotics) according to the individual specificities of the vaginal microbiome.

The Impact of Female Genital Microbiota on Fertility and Assisted Reproductive Treatments

Objective: To review publish data about human microbiome. It is known to modulate many body functions. In the field of Reproductive Medicine, the main question is in what extent may female genital tract microbiome influence fertility, both by spontaneous conception or after Assisted Reproductive Treatments (ART). The aim of this work is to review publish data about this matter. Materials and methods: This is a systematic review on the effect of the microbiota of the female genital tract on human fertility and on the outcomes of ART. Results: Fourteen articles were retrieved, concerning female lower genital tract and endometrium microbiota, including 5 case-controls studies about its impact on fertility, 8 cohort studies regarding ART outcomes and 1 mixed study. The main variables considered were richness and diversity of species, Lactobacillus dominance and the role of other bacteria. Results and conclusions of the various studies were quite diverse and incoherent. Despite the inconsistency of the studies, it seems that vaginal, cervical and endometrial microbiome may eventually play a role. Whether high richness and diversity of species, low amounts of Lactobacillus spp. or the presence of other bacteria, such as Gardnerella spp., may adversely affect reproductive outcomes is not clear. Conclusion: The influence of female genital microbiota on the ability to conceive is still unclear, due to the paucity and inconsistency of published data.

Is there evidence for bacterial transfer via the placenta and any role in the colonization of the infant gut? - a systematic review

With the important role of the gut microbiome in health and disease, it is crucial to understand key factors that establish the microbial community, including gut colonization during infancy. It has been suggested that the first bacterial exposure is via a placental microbiome. However, despite many publications, the robustness of the evidence for the placental microbiome and transfer of bacteria from the placenta to the infant gut is unclear and hence the concept disputed. Therefore, we conducted a systematic review of the evidence for the role of the placental, amniotic fluid and cord blood microbiome in healthy mothers in the colonization of the infant gut. Most of the papers which were fully assessed considered placental tissue, but some studied amniotic fluid or cord blood. Great variability in methodology was observed especially regarding sample storage conditions, DNA/RNA extraction, and microbiome characterization. No study clearly considered transfer of the normal placental microbiome to the infant gut. Moreover, some studies in the review and others published subsequently reported little evidence for a placental microbiome in comparison to negative controls. In conclusion, current data are limited and provide no conclusive evidence that there is a normal placental microbiome which has any role in colonization of infant gut.

Recent advances and future directions for uterine diseases diagnosis, pathogenesis, and management in dairy cows

Researchers, veterinarians, and farmers' pursuit of a consistent diagnosis, treatment, and prevention of uterine diseases remains challenging. The diagnosis and treatment of metritis is inconsistent, a concerning situation when considered the global threat of antimicrobial resistance dissemination. Endometritis is an insidious disease absent on routine health programs in many dairy farms and from pharmaceutical therapeutics arsenal in places like the US market. Conversely, a multitude of studies advanced the understanding of how uterine diseases compromise oocyte, follicle, and embryo development, and the uterine environment having long-lasting effects on fertility. The field of uterine disease microbiome also experienced tremendous progress and created opportunities for the development of novel preventives to improve the management of uterine diseases. Activity monitors, biomarkers, genomic selection, and machine learning predictive models are other innovative developments that have been explored in recent years to help mitigate the negative impacts of uterine diseases. Albeit novel tools such as vaccines for metritis, immune modulators, probiotics, genomic selection, and selective antimicrobial therapy are promising, further research is warranted to implement these technologies in a systematic and cost-effective manner.

The reproductive microbiome - clinical practice recommendations for fertility specialists

The interest in and understanding of the human microbiome has grown remarkably over recent years. Advances in molecular techniques have allowed researchers to identify and study the microbiota and also use this information to develop therapeutic solutions for a spectrum of conditions. Alongside the growing interest in the microbiome, societal changes have resulted in many couples looking to start families later in life, therefore increasing the demand for assisted reproductive technologies. Combining these trends, it makes sense that clinicians are eager to understand and exploit the microbiome of their patients, i.e. the reproductive microbiome, in order to help them achieve their goal of becoming parents. This paper aims to provide an overview of the current and future research into the reproductive microbiome in relation to fertility and also share clinical practice recommendations for physicians who are new to this field or unsure about how they can utilise what is known to help their patients.

Maternal Microbiota, Cortisol Concentration, and Post-Partum Weight Recovery are Dependent on Mode of Delivery

The importance of the maternal microbiota in terms of the initial bacterial seeding has previously been highlighted; however, little is currently known about the perinatal factors that could affect it. The aim of this study was to evaluate the effects of various delivery-related factors on the intestinal microbiome at delivery time and on post-partum weight retention. Data were collected from mothers (n = 167) during the first four months post-partum. A subset of 100 mothers were selected for the determination of the salivary cortisol concentration and microbiome composition at birth by 16S rRNA gene sequencing. The maternal microbiota was classified into two distinct clusters with significant differences in microbial composition and diversity. Maternal microbiota was also significantly influenced by the mode of delivery. Moreover, the salivary cortisol concentration was associated with some maternal microbiota genera and it was significantly higher in the vaginal delivery group (p = 0.003). The vaginal delivery group exhibited lower post-partum weight retention than the C-section (CS) mothers at four months post-partum (p < 0.001). These results support the hypothesis that the mode of delivery as well as the codominant hormonal changes could influence the maternal microbiota and possibly impact maternal weight recovery during the post-partum period.

Characterizing the gut microbiota in females with infertility and preliminary results of a water-soluble dietary fiber intervention study

Despite the advances in assisted reproductive technology, approximately 8-12% of the individuals worldwide who are willing to conceive are unable to do so. Fertility depends on a receptive state of the endometrium and hormonal adaptations as well as the immune system. Local and systemic immunities are greatly influenced by the microbiota. The aim of the present study was to compare the gut microbiota in female patients with that in infertility with fertile control subjects and to evaluate the effect of prebiotic partially hydrolyzed guar gum supplementation on gut dysbiosis and the outcome of pregnancy in patients treated with assisted reproductive technology. Dietary fiber can reconstitute the host intestinal microbiota and modify the immune function; however, clinical data regarding the effect of dietary fiber treatment on the success of assisted reproductive technology is lacking. To investigate the gut microbiota in fertile and infertile females, we conducted 16S metagenomic analysis of fecal samples. In total 18 fertile female subjects and 18 patients with infertility matched by age were recruited, and fecal samples were obtained to analyze the gut microbiome using 16S rRNA V3-V4 sequencing. The unweighted and weighted principal coordinate analyses showed a trend indicating microbial structural differences in β-diversity between these two groups. The abundance of the phylum Verrucomicrobia was higher in patients with infertility. At the genus level, a decrease in the abundance of the genera Stenotrophomonas, Streptococcus, and Roseburia and an increase in the abundance of the genera Unclassified [Barnesiellaceae] and Phascolarctobacterium was observed in patients with infertility. Twelve patients agreed to receive the combined therapy comprising embryo transfer by assisted reproductive technology and oral supplementation with partially hydrolyzed guar gum. The success of pregnancy by this combined therapy was 58.3% (7/12), and the failure was 41.7% (5/12). Predictive factors for pregnancy before treatment were characterized by a decrease in the abundance of Paraprevotella and Blautia and an increase in the abundance of Bifidobacterium. Predictive factors for pregnancy before treatment were characterized by a decrease in the abundance of Paraprevotella and Blautia and an increase tendency in the abundance of Bifidobacterium. In conclusion, the present study showed differences in the abundance of gut microbiota between fertile and infertile groups; moreover, partially hydrolyzed guar gum supplementation helped improve gut dysbiosis and the success of pregnancy in females with infertility.

Alterations in Vaginal Microbiota and Associated Metabolome in Women with Recurrent Implantation Failure

In vitro fertilization-embryo transfer (IVF-ET) is now widely applied for treating infertility, and unexplained recurrent implantation failure (RIF) has become a substantial challenge. We hypothesize that vaginal microbial dysbiosis is associated with RIF, as it is linked to many female reproductive diseases. In this study, we characterized the vaginal microbiota and metabolomes of patients with unexplained RIF, while patients who achieved clinical pregnancy in the first IVF cycle were set as controls. In general, significant differences were discovered in the vaginal microbiota and metabolomes between the two groups. This study is the first detailed elaboration of the vaginal microbiota and metabolites associated with RIF. We believe that our findings will inspire researchers to consider the dynamics of microbiomes related to the microenvironment as a critical feature for future studies of nosogenesis not only for RIF but also for other reproductive diseases.

Recurrent implantation failure (RIF) refers to repeated failure to become pregnant after transferring embryos with normal morphology. However, the pathogenesis of RIF remains unrevealed, especially for those without any pathological features. In this study, we characterized the vaginal microbiota and metabolomes of patients with unexplained RIF, while patients who achieved clinical pregnancy in the first frozen embryo transfer (FET) cycle were used as controls. Based on 16S rRNA gene sequencing of the vaginal microbiota, the vaginal Lactobacillus showed a significant positive correlation with the pregnancy rate, and the RIF group presented higher microbial α-diversity than the control group (P value = 0.016). The metabolomic profile identified 2,507 metabolites, of which 37 were significantly different between the two groups (P value < 0.05, variable importance for the projection [VIP] > 1). Among them, 2′,3-cyclic UMP and inositol phosphate were the top two metabolites that were higher in the RIF group, while glycerophospholipids and benzopyran were important metabolites that were lower in the RIF group. A lack of lysobisphosphatidic acid and prostaglandin metabolized from glycerophospholipids will lead to deferred implantation and embryo crowding. Benzopyran, as a selective estrogen receptor modulator, may affect the outcome of pregnancy. All of the changes in metabolite profiles may result in or from the differential microbiota compositions in RIF patients. In conclusion, significant differences were presented in the vaginal microbiota and metabolomes between patients with unexplained RIF and women who became pregnant in the first FET cycle. For the first time, this study elaborates the possible pathogenesis of RIF by investigating the vaginal microbiota and metabolites in RIF patients.

Microbiota and Human Reproduction: The Case of Female Infertility

During the last decade, the availability of next-generation sequencing-based approaches has revealed the presence of microbial communities in almost all the human body, including the reproductive tract. As for other body sites, this resident microbiota has been involved in the maintenance of a healthy status. As a consequence, alterations due to internal or external factors may lead to microbial dysbiosis and to the development of pathologies. Female reproductive microbiota has also been suggested to affect infertility, and it may play a key role in the success of assisted reproductive technologies, such as embryo implantation and pregnancy care. While the vaginal microbiota is well described, the uterine microbiota is underexplored. This could be due to technical issues, as the uterus is a low biomass environment. Here, we review the state of the art regarding the role of the female reproductive system microbiota in women's health and human reproduction, highlighting its contribution to infertility.

Increased prevalence of endocervical Mycoplasma and Ureaplasma colonization in infertile women with tubal factor

Objective

Most women suffering from tubal factor infertility do not have a history of pelvic inflammatory disease, but rather have asymptomatic upper genital tract infection. Investigating the impacts of such infections, even in the absence of clinically confirmed pelvic inflammatory disease, is critical to understanding the tubal factor of infertility. The aim of this study was to investigate whether the presence of endocervical bacteria is associated with tubal factors in women screened for infertility.

Methods

This retrospective cross-sectional study involved 245 women undergoing hysterosalpingography (HSG), screened for endocervical colonization by Chlamydia trachomatis, Neisseria gonorrhea, Ureaplasma urealyticum and Mycoplasma hominis, as part of a routine female infertility investigation between 2016 and 2017.

Results

endocervical bacterial colonization by Chlamydia trachomatis, Ureaplasma urealiticum, Mycoplasma hominis and other bacteria corresponded to 3.7%, 9.0%; 5.7% and 9.8%, respectively. There was no colonization by Neisseria gonorrhea. The prevalence of tubal factor was significantly higher in patients with positive endocervical bacteria colonization, regardless of bacterial species. When evaluating bacteria species individually, the women who were positive for endocervical Mycoplasma hominis had significantly higher rates of tubal factor. Associations between endocervical bacterial colonization and tubal factor infertility were confirmed by multiple regression analysis adjusted for age and duration of infertility.

Conclusion

Besides the higher prevalence of Mycoplasma and Ureaplasma infectious agents, the findings of this study suggest the possible association of endocervical bacterial colonization - not only Chlamydia trachomatis and Neisseria gonorrhea, but also Mycoplasma species with tubal performance.

Microbiota and Human Reproduction: The Case of Male Infertility

The increasing interest in metagenomics is enhancing our knowledge regarding the composition and role of the microbiota in human physiology and pathology. Indeed, microbes have been reported to play a role in several diseases, including infertility. In particular, the male seminal microbiota has been suggested as an important factor able to influence couple’s health and pregnancy outcomes, as well as offspring health. Nevertheless, few studies have been carried out to date to deeper investigate semen microbiome origins and functions, and its correlations with the partner’s reproductive tract microbiome. Here, we report the state of the art regarding the male reproductive system microbiome and its alterations in infertility.

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

Current knowledge suggests that the uterus harbours its own microbiota, where the microbes could influence the uterine functions in health and disease; however, the core uterine microbial composition and the host-microbial relationships remain to be fully elucidated. Different studies are indicating, based on next-generation sequencing techniques, that microbial dysbiosis could be associated with several gynaecological disorders, such as endometriosis, chronic endometritis, dysfunctional menstrual bleeding, endometrial cancer, and infertility. Treatments using antibiotics and probiotics and/or prebiotics for endometrial microbial dysbiosis are being applied. Nevertheless there is no unified protocol for assessing the endometrial dysbiosis and no optimal treatment protocol for the established dysbiosis. With this review we outline the microbes (mostly bacteria) identified in the endometrial microbiome studies, the current treatments offered for bacterial dysbiosis in the clinical setting, and the future possibilities such as pro- and prebiotics and microbial transplants for modifying uterine microbial composition.

The Interplay Between Reproductive Tract Microbiota and Immunological System in Human Reproduction

In the last decade, the microbiota, i.e., combined populations of microorganisms living inside and on the surface of the human body, has increasingly attracted attention of researchers in the medical field. Indeed, since the completion of the Human Microbiome Project, insight and interest in the role of microbiota in health and disease, also through study of its combined genomes, the microbiome, has been steadily expanding. One less explored field of microbiome research has been the female reproductive tract. Research mainly from the past decade suggests that microbial communities residing in the reproductive tract represent a large proportion of the female microbial network and appear to be involved in reproductive failure and pregnancy complications. Microbiome research is facing technological and methodological challenges, as detection techniques and analysis methods are far from being standardized. A further hurdle is understanding the complex host-microbiota interaction and the confounding effect of a multitude of constitutional and environmental factors. A key regulator of this interaction is the maternal immune system that, during the peri-conceptional stage and even more so during pregnancy, undergoes considerable modulation. This review aims to summarize the current literature on reproductive tract microbiota describing the composition of microbiota in different anatomical locations (vagina, cervix, endometrium, and placenta). We also discuss putative mechanisms of interaction between such microbial communities and various aspects of the immune system, with a focus on the characteristic immunological changes during normal pregnancy. Furthermore, we discuss how abnormal microbiota composition, “dysbiosis,” is linked to a spectrum of clinical disorders related to the female reproductive system and how the maternal immune system is involved. Finally, based on the data presented in this review, the future perspectives in diagnostic approaches, research directions and therapeutic opportunities are explored.

Prospects of NSAIDs administration as double-edged agents against endometrial cancer and pathological species of the uterine microbiome

Many types of cancers, including endometrial cancer, were found to have cyclooxygenase-2 (COX-2) overexpression. Because this enzyme belongs to the group of pro-inflammatory enzymes, so-called NSAIDs (non-steroidal anti–inflammatory drugs) directly inhibit its activity. An increasing number of reports on COX-2 involvement in cancer, as well as on the role of microbiota in abnormal metabolism and signaling of cells, forces the development of new NSAID types. Besides, NSAIDs can affect some bacteria, which are vaginal/endometrial microbiome members. The overgrowth of those species was found to be a major cause of some uterus diseases. Those infections can lead to chronic inflammatory response and suppress anti-tumorigenic cell pathways. The purpose of this review is to highlight the COX-2 enzyme role in endometrial cancer, the potential effect of the endometrial microbiome on COX-2 enzyme overexpression, and the prospects of NSAIDs use in terms of this type of cancer.

Persistent Breeding-Induced Endometritis in Mares - a Multifaceted Challenge: From Clinical Aspects to Immunopathogenesis and Pathobiology

Post-breeding endometritis (i.e., inflammation/infection of the endometrium), is a physiological reaction taking place in the endometrium of mares within 48 hours post-breeding, aimed to clear seminal plasma, excess sperm, microorganisms, and debris from the uterine lumen in preparation for the arrival of an embryo. Mares are classified as susceptible or resistant to persistent breeding-induced endometritis (PBIE) based on their ability to clear this inflammation/infection by 48 hours post-breeding. Mares susceptible to PBIE, or those with difficulty clearing infection/inflammation, have a deficient immune response and compromised physical mechanisms of defense against infection. Molecular pathways of the innate immune response known to be involved in PBIE are discussed herein. The role of the adaptive uterine immune response on PBIE remains to be elucidated in horses. Advances in the pathobiology of microbes involved in PBIE are also revised here. Traditional and non-traditional therapeutic modalities for endometritis are contrasted and described in the context of clinical and molecular aspects. In recent years, the lack of efficacy of traditional therapeutic modalities, alongside the ever-increasing incidence of antibiotic-resistant microorganisms, has enforced the development of non-traditional therapies. Novel biological products capable of modulating the endometrial inflammatory response are also discussed here as part of the non-traditional therapies for endometritis.

Pre-Eclampsia: Microbiota possibly playing a role

Pre-eclampsia (PE) is a complication of pregnancy that is associated with mortality and morbidity in mothers and fetuses worldwide. Oxygen dysregulation in the placenta, abnormal remodeling of the spiral artery, defective placentation, oxidative stress at the fetal-maternal border, inflammation and angiogenic impairment in the maternal circulation are the main causes of this syndrome. These events result in a systemic and diffuse endothelial cell dysfunction, an essential pathophysiological feature of PE. The impact of bacteria on the multifactorial pathway of PE is the recent focus of scientific inquiry since microbes may cause each of the aforementioned features. Microbes and their derivatives by producing antigens and other inflammatory factors may trigger infection and inflammatory responses. A mother's bacterial communities in the oral cavity, gut, vagina, cervix and uterine along with the placenta and amniotic fluid microbiota may be involved in the development of PE. Here, we review the mechanistic and pathogenic role of bacteria in the development of PE. Then, we highlight the impact of alterations in a set of maternal microbiota (dysbiosis) on the pathogenesis of PE.

Uterine Luminal Epithelium as the Transient Gateway for Embryo Implantation

The uterine luminal epithelium (LE) is the first maternal contact for an implanting embryo. Intrauterine fluid resorption, cessation of LE proliferation and apoptosis, and LE structural changes are prerequisites for establishing transient uterine receptivity for embryo implantation. Vesicle trafficking in the LE and receptor-mediated paracrine and autocrine mechanisms are crucial both for LE preparation and LE communications with the embryo and stroma during the initiation of embryo implantation. This review mainly covers recent in vivo studies in LE of mouse models from 0.5 days post-coitus (D0.5) to ∼D4 20 h when the trophoblasts pass through the LE layer for embryo implantation. The review is organized into three interconnected sections: preimplantation LE preparation for embryo attachment, embryo-LE communications, and LE-stroma communications.

Immunological Role of the Maternal Uterine Microbiome in Pregnancy: Pregnancies Pathologies and Alterated Microbiota

Understanding what happens at the time of embryo implantation has been the subject of significant research. Investigators from many differing fields including maternal fetal medicine, microbiology, genetics, reproductive endocrinology and immunology have all been studying the moment the embryo interacts with the maternal endometrium. A perfect relationship between the uterus and the embryo, mediated by a tightly controlled interaction between the embryo and the endometrium, is required for successful implantation. Any factors affecting this communication, such as altered microbiome may lead to poor reproductive outcomes. Current theories suggest that altered microbiota may trigger an inflammatory response in the endometrium that affects the success of embryo implantation, as inflammatory mediators are tightly regulated during the adhesion of the blastocyst to the epithelial endometrial wall. In this review, we will highlight the various microbiome found during the periconceptual period, the microbiomes interaction with immunological responses surrounding the time of implantation, its effect on implantation, placentation and ultimately maternal and neonatal outcomes.

Human Endometrial Microbiota at Term of Normal Pregnancies

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.

The seminal microbiome in health and disease

Owing to the fact that there are more microbial than human cells in our body and that humans contain more microbial than human genes, the microbiome has huge potential to influence human physiology, both in health and in disease. The use of next-generation sequencing technologies has helped to elucidate functional, quantitative and mechanistic aspects of the complex microorganism-host interactions that underlie human physiology and pathophysiology. The microbiome of semen is a field of increasing scientific interest, although this microbial niche is currently understudied compared with other areas of microbiome research. However, emerging evidence is beginning to indicate that the seminal microbiome has important implications for the reproductive health of men, the health of the couple and even the health of offspring, owing to transfer of microorganisms to the partner and offspring. As this field expands, further carefully designed and well-powered studies are required to unravel the true nature and role of the seminal microbiome.

The role of uterine microbiome and epithelial-mesenchymal transition in endometrial function

Reproductive period in woman is characterized by cyclic changes of endometrium and its regeneration. The factors important for proper function of the endometrium are anatomical structure, hormonal control and signalling pathways on molecular-genetic level. New knowledge on uterine microbiome, mutual epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) of endometrial cells refine our conception of changes on cellular level, endometrial receptivity and possible causes of endometrial dysfunction. Substantial information on bacterial colonisation of endometrium were discovered by new diagnostic methods using analysis of ribosomal RNA in 16S subunit which are able to detect and exactly identify bacteria that are not detectable by classic cultivation methods. Endometrial microbiome prevents development of pathogenous microorganisms and modulates function of endometrial cells. It has been proven that stromal cells contribute to regeneration of not only the endometrial stroma, but also of the epithelium. Activity of ovarian steroids and other factors leads to EMT/MET, which ensures different functions of endometrium throughout the menstrual cycle and pregnancy. The endometrial microbiome and mutual transition of stromal and epithelial endometrial cells are necessary for physiological functions of uterine mucosa including implantation and development of an embryo.

Running title: Microbiome and cells transition in endometrial function

Investigating the Optimal Time for Intrauterine Human Chorionic Gonadotropin Infusion in Order to Improve IVF Outcome: A Systematic Review and Meta-Analysis

BACKGROUND/AIM

Studies on the impact of intrauterine human Chorionic Gonadotropin (hCG) administration in order to improve the In Vitro Fertilization (IVF) outcome have yielded conflicting results. The aim of the present systematic review and meta-analysis is to investigate whether timing of intrauterine hCG administration prior to embryo transfer affects its efficiency.

MATERIALS AND METHODS

A systematic search of the literature on Pubmed/Medline, Embase and Cochrane databases was performed. Only Randomized Control Trials were included in this meta-analysis.

RESULTS

Live birth rates were not improved following hCG administration (RR=1.13, 95%CI=0.88-1.46, p=0.34) in the pooled results. Combined live birth and ongoing pregnancy rates were borderline statistically significant following hCG administration (RR=1.27, 95%CI=1.00-1.62, p=0.05). Following subgroup analysis regarding live birth and ongoing pregnancy rates, only the 5-12 minutes prior to the embryo transfer group reported a statistically significant improvement.

CONCLUSION

Intrauterine infusion of hCG within an IVF-Intracytoplasmic Sperm Injection (ICSI) cycle improves outcome only when administered 5-12 min prior to embryo transfer.

The Cancer Microbiota: EMT and Inflammation as Shared Molecular Mechanisms Associated with Plasticity and Progression

With the advent of novel molecular platforms for high-throughput/next-generation sequencing, the communities of commensal and pathogenic microorganisms that inhabit the human body have been defined in depth. In the last decade, the role of microbiota-host interactions in driving human cancer plasticity and malignant progression has been well documented. Germ-free preclinical models provided an invaluable tool to demonstrate that the human microbiota can confer susceptibility to various types of cancer and can also modulate the host response to therapeutic treatments. Of interest, besides the detrimental effects of dysbiosis on cancer etiopathogenesis, specific microorganisms have been shown to exert protective activities against cancer growth. This has strong clinical implications, as restoration of the physiologic microbiota is being rapidly implemented as a novel anticancer therapeutic strategy. Here, we reviewed past and recent literature depicting the role of microbiota-host interactions in modulating key molecular mechanisms that drive human cancer plasticity and lead to malignant progression. We analyzed microbiota-host interactions occurring in the gut as well as in other anatomic sites, such as oral and nasal cavities, lungs, breast, esophagus, stomach, reproductive tract, and skin. We revealed a common ground of biological alterations and pathways modulated by a dysbiotic microbiota and potentially involved in the control of cancer progression. The molecular mechanisms most frequently affected by the pathogenic microorganisms to induce malignant progression involve epithelial-mesenchymal transition- (EMT-) dependent barrier alterations and tumor-promoting inflammation. This evidence may pave the way to better stratify high-risk cancer patients based on unique microenvironmental/microbial signatures and to develop novel, personalized, biological therapies.

Maternal microbiome and the hypertensive disorder of pregnancy, preeclampsia

Preeclampsia (PE) is a pregnancy-specific disorder that can be life threatening for both mother and baby. It is characterized by a new onset hypertension during the second half of pregnancy and affects ~300,000 women in the United States every year. There is no cure for PE, and the only effective treatment is delivery of the placenta and the fetus, which is often preterm. PE is believed to be a severe manifestation of placental dysfunction due to early angiogenic imbalances and inflammatory disturbances; however, the cause of this is unknown. The once thought "sterile" placenta now has been proposed to have a unique microbiome of its own. Under ideal conditions, the microbiome represents a balanced bacterial community that is important to the maintenance of a healthy environment. Dysbiosis of these communities may lead to inflammation that potentially contributes to adverse pregnancy outcomes, such as preterm birth and PE. Thus far, the female reproductive tract microbiome has been found to be influenced by periodontal disease, cardiometabolic complications, and maternal obesity, all of which have been identified as contributors to PE. This review will look at the maternal reproductive tract microbiome, evidence for and against, and its role in pregnancy and PE-related events as well as data from relevant mouse models that could be useful for further investigating the influence of the reproductive tract microbiome on the pathogenesis of PE.

Uterine Immunity and Microbiota: A Shifting Paradigm

The female reproductive tract harbors distinct microbial communities, as in the vagina, cervical canal, uterus, and fallopian tubes. The nature of the vaginal microbiota is well-known; in contrast, the upper reproductive tract remains largely unexplored. Alteration in the uterine microbiota, which is dependent on the nutrients and hormones available to the uterus, is likely to play an important role in uterine-related diseases such as hysteromyoma, adenomyosis, and endometriosis. Uterine mucosa is an important tissue barrier whose main function is to offer protection against pathogens and other toxic factors, while maintaining a symbiotic relationship with commensal microbes. These characteristics are shared by all the mucosal tissues; however, the uterine mucosa is unique since it changes cyclically during the menstrual cycle as well as pregnancy. The immune system, besides its role in the defense process, plays crucial roles in reproduction as it ensures local immune tolerance to fetal/paternal antigens, trophoblast invasion, and vascular remodeling. The human endometrium contains a conspicuous number of immune cells, mainly Natural Killers (NK) cells, which are phenotypically distinct from peripheral cytotoxic NK, cells and macrophages. The endometrium also contains few lymphoid aggregates comprising B cell and CD8⁺ T cells. The number and the phenotype of these cells change during the menstrual cycle. It has become evident in recent years that the immune cell phenotype and function can be influenced by microbiota. Immune cells can sense the presence of microbes through their pattern recognition receptors, setting up host-microbe interaction. The microbiota exerts an appropriately controlled defense mechanism by competing for nutrients and mucosal space with pathogens. It has recently been considered that uterus is a non-sterile compartment since it seems to possess its own microbiota. There has been an increasing interest in characterizing the nature of microbial colonization within the uterus and its apparent impact on fertility and pregnancy. This review will examine the potential relationship between the uterine microbiota and the immune cells present in the local environment.

The Development of the Human Microbiome: Why Moms Matter

The human body is cohabitated with trillions of commensal bacteria that are essential for our health. However, certain bacteria can also cause diseases in the human host. Before the microbiome can be attributed to disease risk and pathogenesis, normal acquisition and development of the microbiome must be understood. Here, we explore the evidence surrounding in utero microbial exposures and the significant of this exposure in the proper development of the fetal and neonatal microbiome. We further explore the development of the fetal and neonatal microbiome and its relationship to preterm birth, feeding practices, and mode of delivery, and maternal diet.

What will the future hold for artificial organs in the service of assisted reproduction: prospects and considerations

Assisted reproduction provides a wide spectrum of treatments and strategies addressing infertility. However, distinct groups of infertile patients with unexplained infertility, congenital disorders, and other complex cases pose a challenge in in vitro fertilization (IVF) practices. This special cohort of patients is associated with futile attempts, IVF overuse, and dead ends in management. Cutting edge research on animal models introduced this concept, along with the development of artificial organs with the aim to mimic the respective physiological functions in reproduction. Extrapolation on clinical application leads to the future use of infertility management in humans. To date, the successful clinical application of artificial reproductive organs in humans is not feasible because further animal model studies are required prior to clinical trials. The application of these artificial organs could provide a solution to infertility cases with no other options. This manuscript presents an overview on the current status, future prospects, and considerations on the potential clinical application of artificial ovary, uterus, and gametes in humans. This paper presents how the IVF practice landscape may be shaped and challenged in the future, along with the subsequent concerns in assisted reproductive treatments.

Role for the mammalian female reproductive tract microbiome in pregnancy outcomes

Since the discovery of the microbiome in humans, it has been studied in many mammalian species. Different microbiological communities with variable richness and diversity have been found among these species in distinct areas of the reproductive tract. Human studies have shown that the composition of the microbiome is dependent on body site and several host-related factors. Furthermore, specific phyla have been identified among the different species and within distinct areas of the female reproductive tract, but a "core" microbiome of the female reproductive tract has not been defined in any species. Moreover, the function of the microbiome in the reproductive tract is not yet fully understood. However, it has been suggested that a change in diversity of the microbiome and the presence or absence of specific microbial species might be useful indicators of pregnancy outcomes. Increased comprehensive knowledge of the microbiological communities in the female reproductive tract is needed since adverse outcomes represent a significant problem to many species, including livestock, exotic or endangered species, and humans. To the authors' knowledge, a review combining current female reproductive tract microbiome data among different mammalian species has not been published yet. Herein is a comprehensive review of what is known in the field of the female reproductive microbiome and how it correlates with reproductive success or failure in mammals. Further studies may lead to optimization of therapies in the treatment of reproductive tract infections and pregnancy failure, and may create opportunities for novel approaches for improving reproductive efficiency in animals and people.

Microorganisms in the healthy upper reproductive tract: from denial to beneficial assignments for reproductive biology

Contrary to the traditional assumption of a sterile uterus, the number of studies characterizing microbial entities in the healthy upper reproductive tract (endometrial cavity, including follicular fluid and placenta) have been on the increase. Substantial data has been accumulated correlating microbial composition with fertility outcome. In this context, the presence of certain taxa was associated to an improved reproductive success. A summarization for the evidence of these molecular mechanisms through which bacteria may affect developmental processes during pregnancy is presented and discussed with special focus placed upon the immunological aspects.

Selection of New Probiotics for Endometrial Health

Microbiota is a crucial player in gynecologic health, in which bacteria can shift to a dysbiotic state triggering a pathogenic process. Based on an ecological understanding of the problem, the aim of this study is to select a potential probiotic strain to improve female reproductive tract based on its capacity to initially lower pH and to promote the reduction of pathogenic bacteria. Based on this rationale, strain Lactobacillus rhamnosus BPL005 was initially selected for its capacity to reduce in vitro pH levels and produce organic acids. Subsequently, strain L. rhamnosus BPL005 (CECT 8800) was demonstrated to have a protective role on endometrial infections in an in vitro model of bacterial colonization of primary endometrial epithelial cells with Atopobium vaginae, Gardnerella vaginalis, Propionibacterium acnes, and Streptococcus agalactiae. In this model, BPL005 when co-cultured with those pathogens was shown to lower pH and to produce organic acids, being lactic acid the most relevant. The co-cultivation of strain L. rhamnosus BPL005 with tested reference pathogens produced a significant reduction in P. acnes and St. agalactiae levels and a non-significant reduction in A. vaginae and G. vaginalis. The colonization of L. rhamnosus BPL005 in the culture decreased IL-6, IL-8, and MCP-1, heightened in the presence of pathogens, and increased IL-1RA and IL-1 beta. Finally, safety was evaluated showing no signs of cytotoxicity, irritation in vaginal tests, or allergic contact dermatitis potential through the Local Lymph Node Assay. Overall, these results show the potential of L. rhamnosus BPL005 strain as a probiotic in gynecological health.

Does the human placenta delivered at term have a microbiota? Results of cultivation, quantitative real-time PCR, 16S rRNA gene sequencing, and metagenomics

BACKGROUND

The human placenta has been traditionally viewed as sterile, and microbial invasion of this organ has been associated with adverse pregnancy outcomes. Yet, recent studies that utilized sequencing techniques reported that the human placenta at term contains a unique microbiota. These conclusions are largely based on the results derived from the sequencing of placental samples. However, such an approach carries the risk of capturing background-contaminating DNA (from DNA extraction kits, polymerase chain reaction reagents, and laboratory environments) when low microbial biomass samples are studied.

OBJECTIVE

To determine whether the human placenta delivered at term in patients without labor who undergo cesarean delivery harbors a resident microbiota ("the assemblage of microorganisms present in a defined niche or environment").

STUDY DESIGN

This cross-sectional study included placentas from 29 women who had a cesarean delivery without labor at term. The study also included technical controls to account for potential background-contaminating DNA, inclusive in DNA extraction kits, polymerase chain reaction reagents, and laboratory environments. Bacterial profiles of placental tissues and background technical controls were characterized and compared with the use of bacterial culture, quantitative real-time polymerase chain reaction, 16S ribosomal RNA gene sequencing, and metagenomic surveys.

RESULTS

(1) Twenty-eight of 29 placental tissues had a negative culture for microorganisms. The microorganisms retrieved by culture from the remaining sample were likely contaminants because corresponding 16S ribosomal RNA genes were not detected in the same sample. (2) Quantitative real-time polymerase chain reaction did not indicate greater abundances of bacterial 16S ribosomal RNA genes in placental tissues than in technical controls. Therefore, there was no evidence of the presence of microorganisms above background contamination from reagents in the placentas. (3) 16S ribosomal RNA gene sequencing did not reveal consistent differences in the composition or structure of bacterial profiles between placental samples and background technical controls. (4) Most of the bacterial sequences obtained from metagenomic surveys of placental tissues were from cyanobacteria, aquatic bacteria, or plant pathogens, which are microbes unlikely to populate the human placenta. Coprobacillus, which constituted 30.5% of the bacterial sequences obtained through metagenomic sequencing of placental samples, was not identified in any of the 16S ribosomal RNA gene surveys of these samples. These observations cast doubt as to whether this organism is really present in the placenta of patients at term not in labor.

CONCLUSION

With the use of multiple modes of microbiologic inquiry, a resident microbiota could not be identified in human placentas delivered at term from women without labor. A consistently significant difference in the abundance and/or presence of a microbiota between placental tissue and background technical controls could not be found. All cultures of placental tissue, except 1, did not yield bacteria. Incorporating technical controls for potential sources of background-contaminating DNA for studies of low microbial biomass samples, such as the placenta, is necessary to derive reliable conclusions.

The relation of the vaginal microbiota to early pregnancy development during in vitro fertilization treatment-A meta-analysis

An abnormal vaginal microbiota composition has been shown to lead to pre-term births, miscarriage, and problems with conceiving. Studies have suggested that dysbiosis reduces successful early pregnancy development during IVF. However, conflicting reports exist. This meta-analysis aims to answer the following question: what is the aggregated effect found by studies investigating the influence of the vaginal microbiota composition on early pregnancy rates after IVF treatment? A systematic review was performed using the Medline and EMBASE databases, using search terms for healthy vaginal microbiota, abnormal vaginal microbiota, fertility and pregnancy. The search resulted in six included articles. Of these, all six were used for further meta-analysis. The main outcome measures were the clinical pregnancy rate, determined through ultrasound proven fetal heartbeat and/or hCG results before 10 weeks gestation, in relation to the vaginal microbiota composition. We found a correlation between abnormal vaginal microbiota and lower rates of early pregnancy development after IVF treatment (OR = 0.70, 95% CI = 0.49 - 0.99). One study showed the reverse correlation. However, heterogeneity between study methodologies in various forms was found. In conclusion, women with an abnormal vaginal microbiota are roughly 1.4 times less likely to have a successful early pregnancy development after IVF treatment when compared to women with normal microbiota.

Shaping Microbiota During the First 1000 Days of Life

The data obtained in prior studies suggest that early microbial exposition begins prior to conception and gestation. Given that the host-microbe interaction is shaped by the immune system response, it is important to understand the key immune system-microbiota relationship during the period from conception to the first years of life. The present work summarizes the available evidence concerning early microbiota exposure within the male and the female reproductive tracts at the point of conception and during gestation, focusing on the potential impact on infant development during the first 1000 days of life. Furthermore, we conclude that some dietary strategies including specific probiotics could become potentially valuable tools to modulate the gut microbiota during this early critical window of opportunity for targeted health outcomes throughout the entire lifespan.