REGULATION OF VAGINAL MICROBIOTA, MICROBIAL BALANCE, AND VAGINAL INFECTIONS

The vaginal microbiota is a dynamic structure that constantly changes depending on many factors. It has a composition with low microbial diversity, often dominated by Lactobacilli. Lactobacillus sp. secrete lactic acid using glycogen stored in the vaginal epithelium, thereby maintaining a vaginal pH below 4.8. This acidic vaginal pH, along with the antimicrobial substances secreted by Lactobacillus sp., prevents the invasion of pathogenic microorganisms. Lactobacillus also secretes various substances that modulate the vaginal immune response and strengthen the mucosal barrier. They also contribute to maintaining vaginal health by competing with pathogenic microorganisms for attachment sites and nutrients. Community State Types (CSTs) have been defined to facilitate the evaluation of the relationships between vaginal microbiota and diseases affecting the female genital organs. Five different CSTs have been identified based on the dominance of different Lactobacillus sp. or different bacteria. Some types are further subdivided into subtypes. Transformations between these types have been observed in various hormonal states, ethnic backgrounds, and disease states. CSTs Ⅰ, Ⅱ, and Ⅴ are frequently associated with healthy vaginal microbiota, while CST Ⅲ is more unstable, and CST Ⅳ is linked to disease states. The vaginal microbiota is mainly regulated by hormonal balance, which changes throughout a woman's life. The main determinant is the level of estrogen, as estrogen levels directly affect the amount of glycogen, the primary food source for Lactobacillus. During childhood, from the neonatal period until puberty, Lactobacillus dominance is absent due to low estrogen levels. With puberty, increased estrogen leads to the dominance of Lactobacillus sp., a decrease in microbial diversity, and an acidic vaginal pH. Changes in microbiota composition are observed during this period due to events such as the menstrual cycle and pregnancy. After menopause, estrogen levels decrease, and simultaneously, Lactobacillus dominance disappears, with increased diversity. In addition, factors such as a woman's ethnicity, dietary habits, and lifestyle can also alter the vaginal microbiota. Vaginal dysbiosis is defined as a loss of Lactobacillus dominance and the proliferation of anaerobic bacteria. This condition increases the risk of bacterial vaginosis, sexually transmitted diseases, pelvic inflammatory disease, and vulvovaginal candidiasis. The loss of Lactobacillus dominance leads to decreased lactic acid production and increased vaginal pH, reduced antimicrobial activity, and consequently, easier invasion by pathogenic microorganisms. This loss of dominance is associated not only with an increased risk of infection but also with a decreased response to treatment and recurrence of infection after treatment. Therefore, maintaining a healthy vaginal microbiota is of paramount importance in the prevention and treatment of vaginal infections.