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A major breakthrough on female reproductive tract microecology
Publish Date: 2017-10-17

---New insights into the continuity of bacterial flora existing in female reproductive tract and its relation with reproductive health


Recently, researchers from BGI and the research team of Prof. Ruifang Wu from Peking University Shenzhen Hospital, reported the completed project of microbiota within female reproductive tract in women of reproductive age. The latest findings were published in Nature Communications.

The aim of this research was to study the distribution of bacterial flora in female reproductive tract and the association with reproductive system diseases by advanced metagenomic sequencing techniques. The results reflect the existence of distinct bacterial communities throughout the female reproductive tract forming a continuum of microbiotas changing from the vagina to the oviduct, which challenge the traditional view of female upper reproductive tract being a sterile event. The researchers revealed the continuity of the bacterial flora structure from vagina to cervical canal, uterus, fallopian tubes and peritoneal fluid for the first time, and also identified relationship between the microenvironment of the female reproductive tract and the disease of reproductive system, health and related diseases.

As we know, female reproductive health is a major social and public health issue on the global, including the prevention and control of reproductive tract diseases, fertility regulation and maternal and child health. According to statistics, the incidence of reproductive diseases in women is as high as 90%, including inflammatory diseases of the reproductive tract, uterine fibroids, endometrial diseases, endometriosis and reproductive tract malignancies and so on. In the traditional view, healthy women regard cervical os as a natural barrier to prevent microorganisms from migrating to the uterine cavity, keeping the upper reproductive tract sterile. In recent years, there have been reports of bacterial flora in normal placenta, amniotic fluid and even tubal tissue. However, owing to the limitations of sampling methods, research methods and sample size, the results of this study are controversial. The particularity and complexity of the anatomical structure of the female upper reproductive tract also greatly increase the difficulty of the study between microecological environment and pathological changes, diagnosis and pathogenesis of related diseases.

To explore the presence of microorganisms in the female reproductive tract, the researchers systematically sampled the microbiota throughout the female reproductive tract of 110 Chinese women within reproductive age (samples from six female reproductive tract locations including lower third of vagina; posterior fornix; cervical mucus; endometrium; fallopian tubes and peritoneal fluid), and examine the nature of colonization by 16S rRNA gene amplicon sequencing and cultivation. The researchers unequivocally demonstrate the existence and viability of diverse bacteria throughout the female reproductive tract which forms a continuum of microbiota from the vagina to around the oviduct. These findings showed that the upper reproductive tract was not a sterile environment, and the microbial species composition in the various parts of the vagina to fallopian tubes and peritoneal fluid presents a gradual change in anatomical structure.

In addition, the researchers offer a quantitative measure for the concordance of samples with and without going through the cervical os, and between the upper and lower reproductive tracts. And due to strong correlations between different sampling sites within the same individual, it provided possibility to use samples from the vaginal or cervical sites to probe diseases in the normally inaccessible uterine and peritoneal sites.

Moreover, with the extensive host metadata collected, the researchers observed that the vagino-uterine microbiota varied with several factors including the menstrual cycle, the number of births a woman has given, diseases (such as hysteromyoma, endometriosis, adenomyosis and infertility). Potential markers for conditions such as adenomyosis and endometriosis were also identified.

This innovative research has enable us to understand the microecological environment of female reproductive tract. The results suggest that many gynecological diseases have different degrees ecological disturbance in reproductive tract. Therefore, the maintenance of micro ecological balance has become an important factor in the prevention and treatment of reproductive system diseases. It is a great significance to comprehensive explore and evaluate micro ecological in reproductive tract for the prevention, treatment and prognosis of reproductive tract related diseases.

“To our knowledge, this is the first and only large reproductive age women cohort with multiple samples from the same individual so far”, Chen Chen, a researcher from BGI, the co-first author of this article, said, “It would be the first time that the existence of a microbiota in the female upper reproductive tract is brought into undeniable attention, even in normal women. Our study provides insight into the nature of the vagino-uterine microbiome, and suggests that surveying the vaginal or cervical microbiota might be useful for detection of microenvironment in the upper reproductive tract.”

“This study demonstrates a microbiota in traditionally unchartered territories, which opens a new direction for the study of female reproductive system, and provides an important basis for the etiology study, early diagnosis and effective intervention of reproductive tract related diseases.” Dr. Huijue Jia, one of the corresponding authors of this paper and project leader of BGI, said in a statement.


Further Reading:

The Microbiota Continuum along the Female Reproductive Tract and Its Relation to Uterine-related Diseases