In this cohort, five major bacterial communities were identified. profiled the microbial composition of healthy 396 north American women in reproductive age ( 4). Many scientists have tried to define optimal vaginal microbial composition despite tremendous difficulty due to the dynamic nature of the vaginal microbiome. Critically, the vaginal microbiome composition dynamically changes in response to various intrinsic and extrinsic factors ( 5, 6). Following the introduction of high throughput sequencing methods, it is now well established that the vaginal microbiome is more diverse than previously thought ( 4, 5, 13). It was initially thought the vaginal microbiome simply consisted of Lactobacillus. Vaginal Microbial CommunityĪ thorough characterization of the optimal/healthy bacterial community is a fundamental issue in vaginal microbiome research. In this review, we discuss current understanding and gaps in knowledge regarding the vaginal microbiome, focusing on host factors that change vaginal microbiome composition and how vaginal microbiome affects host reproductive homeostasis and disease. Thus, there is an urgent need to understand mechanisms underlying the association between vaginal microbiome and its related diseases.
This lack of experimental evidence makes it difficult to develop new diagnostic and therapeutic tools. However, most of these correlational results were not supported by experimental study using animal models due to the uniqueness of human vaginal microbiome. Furthermore, numerous observational studies have highlighted that a non- Lactobacillus dominant vaginal microbiome is correlated with various diseases, including sexually transmitted infections (STIs), gynecologic cancer, infertility, and preterm birth ( 7– 12). With the introduction and rapid advancement of high throughput sequencing methodologies, it is now widely accepted that the vaginal microbiome is more diverse and highly dynamic than previously assumed ( 4– 6). These fundamental findings formed the basis of our current knowledge that Lactobacillus is the most prevalent bacteria in vagina and is central for women`s health. Döderlein also discovered Döderlein`s bacillus had an antagonistic action on Staphylococcus growth and the absence of Döderlein`s bacillus in vaginal fluid was associated with puerperal fever ( 2, 3). This bacterium was called Döderlein`s bacillus at the time of its discovery, but it was later renamed Lactobacillus due to its ability to produce lactic acid. The presence of vaginal microbiota was first observed in 1892, when German obstetrician/gynecologist Albert Döderlein identified a gram-positive, non-spore forming rod in the vaginal fluid ( 1). A better understanding of relationship between host and vaginal microbiome could identify novel targets for diagnosis, prognosis, or treatment of microbiome-related diseases. In this review, we highlight the current knowledge of how host factors modulate vaginal microbiome composition and how the vaginal microbiome contributes to maintaining homeostasis or inducing pathogenesis. Depending on these fluctuations, the vaginal microbiome composition can shift temporally and dynamically. The female reproductive tract undergoes constant fluctuations due to hormonal cycle, pregnancy, and other extrinsic factors. Furthermore, numerous epidemiologic studies also have demonstrated various host factors regulate the vaginal microbiome. Because of this, numerous studies focused on the impact of the vaginal microbiome on women`s health and disease. Bacterial vaginosis can modulate host immune systems, and is frequently associated with various aspects of disease, including sexually transmitted infection, gynecologic cancer, and poor pregnancy outcomes. Host cells provide Lactobacillus glycogen as an energy source, and Lactobacillus produce lactic acid, which lowers vaginal pH thereby preventing growth of other bacteria. The host and vaginal microbiome mutually coexist in the vaginal microenvironment. The human vaginal microbiome exhibits a low diversity and is dominated by Lactobacillus species, compared to the microbiome of other organs. The female reproductive tract harbors a unique microbiome, especially the vagina. Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea.
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