Abstract
Changes in the female genital tract microbiome are consistently correlated to gynecological and obstetrical pathologies, and tract dysbiosis can impact reproductive outcomes during fertility treatment. Nonetheless, a consensus regarding the physiological microbiome core inside the uterine cavity has not been reached due to a myriad of study limitations, such as sample size and experimental design variations, and the influence of endometrial bacterial communities on human reproduction remains debated. Understanding the healthy endometrial microbiota and how changes in its composition affect fertility would potentially allow personalized treatment through microbiome management during assisted reproductive therapies, ultimately leading to improvement of clinical outcomes. Here, we review current knowledge regarding the uterine microbiota and how it relates to human conception.
Highlights
Treatment revealed a decrease in Lactobacillus spp. abundance among patients diagnosed with endometritis through CD138 immunohistochemistry, while Ralstonia spp. and Gardnerella spp. were associated with chronic endometritis (CE) [69]; and higher numbers of Phyllobacterium and Sphingomonas are reported in CE patients [70]
With increasing knowledge about bacterial communities related to CE, molecular microbiology represents a feasible tool for CE diagnosis
Improvements in CE diagnostics and treatment may yield important changes in reproductive outcomes, as infertility conditions such as repeated implantation failure (RIF) are consistently related to CE [55,73,74]
Summary
The human microbiome was first described as “the ecological community of commensal, symbiotic, and pathogenic microorganisms that literally share our body space” [1]. The. Human Microbiome Project (HMP) [2] initiated the gathering of deep knowledge about the microbiota in different body sites, but how to define a healthy bacterial composition of the uterus remains under debate. With the advent of next-generation sequencing (NGS), techniques such as 16S rRNA gene sequencing enabled many studies to describe different microbial communities inside the uterine cavity, yet it is unclear where these originate. Regardless of its origin, research consistently demonstrates that the uterine microbiome is highly diverse and scarcely populated compared with the lower genital tract [9,10,11], but its composition remains to be fully unraveled
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