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

The Microbial Composition of Lower Genital Tract May Affect the Outcome of in vitro Fertilization-Embryo Transfer

Objective: This work was conducted in order to study the effect of the lower genital tract (vaginal and cervical canal) microbiota on pregnancy outcomes of reproductive-aged women receiving embryo transfer.

Study design: A total of 150 reproductive-aged patients who received the first fresh in vitro fertilization-embryo transfer (IVF-ET) were included in the study. Samples from the vagina and cervical site of each patient were collected separately using sterile swabs before ET. Genomic DNA was pyrosequenced for the V3–V4 regions of the 16S ribosomal RNA gene. Further bioinformatics analysis was performed using QIIME and R package. Pregnancy outcomes were followed and analyzed to compare differences in microbial composition.

Results: The cervical microbiota had a higher Shannon index than the vaginal microbiota, and the microbial composition was different between the two sites. However, the Sorenson index between the two sites within the same individual was 0.370 (0.309–0.400). A total of 89 patients achieved clinical pregnancy after ET, while 61 failed. The Shannon indices and the microbial community of both vaginal and cervical microbiota between pregnant and non-pregnant groups were not significantly different. The relative abundance of Lactobacillus in the vagina and cervical canal did not differ between the two groups. Linear discriminant analysis, random forest analysis, and receiver-operating characteristic curve analysis showed that Bifidobacterium, Prevotella, and Lactobacillus iners in the vagina, as well as Solanum torvum, Fusobacterium, and Streptococcus in the cervix, may be negatively associated with clinical pregnancy after IVF.

Conclusion: The cervical microbiota was more diverse than the vaginal microbiota, but because of anatomical continuity, there was a correlation between the two sites. The microbial composition of the vagina and cervical canal may influence the outcome of IVF-ET, but more samples are needed to verify this conclusion.

Potential biomarkers of infertility associated with microbiome imbalances

PROBLEM

The aim of this study was to investigate the possible relationship between vaginal/rectal microbiome disbalances and miRNA expression with infertility.

METHOD OF STUDY

Observational, exploratory, preliminary study. A total of 287 multiple IVF failure infertile patients were recruited. Twenty fertile women, not IVF failure, were recruited as the control group. Swab samples were collected from the vagina and rectum. Microbial composition by NGS and miRNA expression by real-time PCR of vaginal and rectal samples was measured. Immunometabolic markers from blood (insulin, vitamin D, LDL-cholesterol, ANA, TPO, Tg, and ASCA antibodies) and saliva (sIgA) were analyzed.

RESULT(S)

Infertile patients showed a lower bacterial richness and increased Firmicutes/Bacteroidetes ratio at rectal level and an increased Lactobacillus brevis/Lactobacillus iners ratio in vaginal samples regarding the fertile group. In the same rectal swab samples, we found that miR-21-5p, which is associated with tight junction disruption and yeast overgrowth, is upregulated and that miR-155-5p, which is associated with inflammation, is overexpressed in the unexplained infertile group (*p < .05). These deregulated miRNAs were also upregulated in the vaginal samples from the same patients (*p < .05).

CONCLUSION

miRNAs could be potential biomarkers of the inflammatory impact of microbiome disbalances in unexplained infertile women.

Biomolecular Markers of Recurrent Implantation Failure-A Review

Currently, infertility affects 8–12% of reproductive age couples worldwide, a problem that also affects women suffering from recurrent implantation failure (RIF). RIF is a complex condition resulting from many physiological and molecular mechanisms involving dynamic endometrium–blastocyst interaction. The most important are the endometrial receptivity process, decidualization, trophoblast invasion, and blastocyst nesting. Although the exact multifactorial pathogenesis of RIF remains unclear, many studies have suggested the association between hormone level imbalance, disturbances of angiogenic and immunomodulatory factors, certain genetic polymorphisms, and occurrence of RIF. These studies were performed in quite small groups. Additionally, the results are inconsistent between ethnicities. The present review briefly summarizes the importance of factors involved in RIF development that could also serve as diagnostic determinants. Moreover, our review could constitute part of a new platform for discovery of novel diagnostic and therapeutic solutions for RIF.

Exploring the global vaginal microbiome and its impact on human health

Around the world, more than 175,000,000 women are diagnosed every year with gynaecological disease, in many cases contributing to high morbidity and mortality. For this reason, knowledge of the composition of the vaginal microbiome and its variations represents a real health challenge, as this is key to improving therapeutic management. This review traces the history of the poorly known vaginal microbiome and focuses on the latest findings concerning this ecosystem. Studies in the past decade have targeted complex bacterial communities within the vagina. However, due to the development of technology and the emergence of next generation sequencing (NGS), the exact definition of the vaginal microbiome has changed and can no longer be linked solely to the presence of bacteria. In order to reach a global view of the vaginal microbiome, it is essential to take into account all microorganisms that the vagina harbours, including fungi, viruses, archaea, and candidate phyla radiation. Although these communities represent only a minimal percentage of the vaginal microbiome, they may act as modifiers of its basic physiology and may play a key role in the maintenance of microbial communities, as well as metabolic and immune functions. Studies of the complex interactions between these different microorganisms have recently begun and are not yet fully understood. Results to date indicate that these microbial communities together constitute the first line of defence against infections. On the other hand, the slightest disturbance in this microbiome may lead to disease. For this reason, enhanced knowledge of these associations is critical to better identify predispositions to certain illnesses, which may open new therapeutic avenues. Currently however, only the tip of the iceberg is understood and current research on this ecosystem is revolutionising our knowledge and understanding of human health and disease.

Characterization of Vaginal Microbiota in Women With Recurrent Spontaneous Abortion That Can Be Modified by Drug Treatment

Objective

The role of vaginal microbiota in recurrent spontaneous abortion (RSA) remains unknown. The purpose of this study was to investigate characteristics of vaginal microbiota and the effects of drug treatment on vaginal microbiota of patients with RSA.

Methods

A case-control study was performed, in which non-pregnant patients who experienced RSA were selected and divided into untreated and drug-treated groups. Drug-treated patients were subdivided into the metformin group, metformin plus aspirin group, and other drugs group. Healthy women who had live births and never experienced spontaneous abortion were enrolled in the control group. Characteristics of vaginal microbiomes of patients with RSA and healthy women and the impact of drug treatment on the microbiome was evaluated via 16S rRNA gene sequencing of the V3-V4 region using the Illumina MiSeq platform.

Results

Women who underwent RSA had lower microbial richness than healthy women. Compared to controls, the relative abundance of seven taxa (Megasphaera, Sneathia sanguinegens, Pseudomonas, Sphingomonas, Rhodococcus, Burkholderia- Caballeronia-Paraburkholderia, and Corynebacterium_1) in the patient's vaginal microbiota changed significantly, which may be closely related to RSA. The composition of the vaginal microbial community in RSA patients was altered by drug treatment. Metformin combined with aspirin treatment significantly increased the relative abundance of vaginal Lactobacillus spp. in patients.

Conclusion

An altered vaginal microbiome composition might be associated with RSA, which could be modified by drug treatment. The effect of metformin combined with aspirin on vaginal Lactobacillus is worthy of attention.

The reproductive tract microbiota in pregnancy

The reproductive tract microbiota plays a crucial role in maintenance of normal pregnancy and influences reproductive outcomes. Microbe–host interactions in pregnancy remain poorly understood and their role in shaping immune modulation is still being uncovered. In this review, we describe the composition of vaginal microbial communities in the reproductive tract and their association with reproductive outcomes. We also consider strategies for manipulating microbiota composition by using live biotherapeutics, selective eradication of pathogenic bacteria with antibiotics and vaginal microbiota transplantation. Finally, future developments in this field and the need for mechanistic studies to explore the functional significance of reproductive tract microbial communities are highlighted.

Analysis of vaginal and endometrial microbiota communities in infertile women with a history of repeated implantation failure

PURPOSE

To identify specific bacterial communities in vaginal and endometrial microbiotas as biomarkers of implantation failure by comprehensively analyzing their microbiotas using next-generation sequencing.

METHODS

We investigated α- and β-diversities of vaginal and endometrial microbiotas using 16S rRNA gene sequencing and compared their profiles between 145 women with repeated implantation failure (RIF) and 21 controls who lacked the factors responsible for implantation failure with a high probability of being healthy and fertile to identify specific bacteria that induce implantation failure.

RESULTS

The endometrial microbiotas had higher α-diversities than did the vaginal microbiotas (P < .001). The microbiota profiles showed that vaginal and endometrial samples in RIF patients had significantly higher levels of 5 and 14 bacterial genera, respectively, than those in controls. Vaginal Lactobacillus rates in RIF patients were significantly lower at 76.4 ± 38.9% compared with those of the controls at 91.8 ± 22.7% (P = .018), but endometrial Lactobacillus rates did not significantly differ between the RIF patients and controls (56.2 ± 36.4% and 58.8 ± 37.0%, respectively, P = .79).

CONCLUSIONS

Impaired microbiota communities containing specific bacteria in both the endometrium and vagina were associated with implantation failure. The vaginal Lactobacillus rates, but not the endometrial, may be a biomarker for RIF.