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Endometrial microbiome

What is the endometrial microbiome and how does it affect fertility?

The Endometrial Microbiome in Human Reproduction cover

A microbial ecosystem that influences woman’s reproductive health

Far from being a sterile organ, the endometrium harbors a thriving ecosystem of microorganisms known as the endometrial microbiome [1]. This microbial community, composed primarily of bacteria and fungi, plays a critical role in women’s reproductive health, influencing fertility, embryo implantation, and all stages of pregnancy.

Which bacterial species form the microbiome?

A healthy endometrial microbiome helps to create a homeostatic environment characterized by a balance between the microbiota and the host. Predominant bacteria include the Lactobacilli, whose abundance positively correlates with better reproductive outcomes [2]. In addition to Lactobacilli, the endometrial microbiome includes additional bacteria and other microorganisms, such as fungi and viruses; the overall balance between these members can determine an optimal or “dysbiotic” endometrial ecosystem [3].

How does the endometrial microbiome influence fertility?

An imbalance in the endometrial microbiome, known as dysbiosis, can negatively affect fertility. The presence of pathogenic bacteria, such as enterobacteria, streptococci, staphylococci, and Gram-negative bacteria, can prompt endometrial infections (such as chronic endometritis) and a significant decrease in implantation and pregnancy rates [4].

Endometrial microbiome research and the advances made

Our research group has been at the forefront of research into the endometrial microbiome and its clinical implications in reproduction. Our findings demonstrate that pathological deviations of Lactobacillus bacteria in the endometrium may play a role in infertility [2].

We aim to apply molecular and cellular microbiology techniques to investigate the interactions between the microbiome and the human endometrium. The results may help to understand the functional impact of bacteria on the origin of infertility (e.g., implantation failure or recurrent miscarriage) and other pathologies (e.g., endometriosis and chronic endometritis). Likewise, this knowledge will facilitate the development of novel therapeutic tools that aim to restore an optimal endometrial microbiota.

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1. Moreno, I., Codoñer, F. M., Vilella, F., Valbuena, D., Martinez-Blanch, J. F., Jimenez-Almazán, J., Alonso, R., Alamá, P., Remohí, J., Pellicer, A., Ramon, D., & Simon, C. (2016). Evidence that the endometrial microbiota has an effect on implantation success or failure. American journal of obstetrics and gynecology, 215(6), 684–703.

2. Moreno, I., Garcia-Grau, I., Perez-Villaroya, D. et al. Endometrial microbiota composition is associated with reproductive outcome in infertile patients. Microbiome 10, 1 (2022).

3. Garcia-Grau, I., Simon, C., & Moreno, I. (2019). Uterine microbiome-low biomass and high expectations. Biology of reproduction, 101(6), 1102–1114.

4. Moreno, I., Cicinelli, E., Garcia-Grau, I., Gonzalez-Monfort, M., Bau, D., Vilella, F., De Ziegler, D., Resta, L., Valbuena, D., & Simon, C. (2018). The diagnosis of chronic endometritis in infertile asymptomatic women: a comparative study of histology, microbial cultures, hysteroscopy, and molecular microbiology. American journal of obstetrics and gynecology, 218(6), 602.e1–602.e16.