Female ecosystem

The female lower reproductive tract is an open lumen and an important microbiota in the human body. Normally, it is a microbiota composed mainly of dominant bacteria such as lactobacilli. People have studied the vaginal microbiota under the health and pathological conditions of women, such as bacterial vaginosis, vulvovaginal candidiasis, and trichomoniasis vaginitis. It has been proven that the vaginal microbiota is a very sensitive system that can easily change when influenced by endogenous and exogenous factors, leading to the occurrence of diseases.

Female anatomical environment

In the female genital area, the labia majoris on both sides naturally close, covering the vaginal opening and urethral opening; The vaginal opening is closed and the anterior and posterior walls of the vagina are tightly attached. The female vaginal wall is composed of intact layered squamous epithelial cells, which can continuously proliferate and thicken with the increase of estrogen levels in the body, and periodically shed with changes in the endocrine cycle. No secretory glands were found in the vagina, but the secretions could come from the vestibular glands, paraurethral glands, cervical mucus, endometrium, fallopian tubes and other parts, and even exuded from the submucosa in the form of "sweating". Healthy women have acidic vaginal secretions and alkaline cervical mucus plugs. These anatomical and physiological characteristics form a natural defense function.

Normal vaginal microbiota status

The normal microbiota in the vagina is the core content of vaginal microecology research. In 1892, Dederlein first published research on the human vaginal microbiota. People have found that the vaginal microbiota of healthy women is composed of various anaerobic and aerobic bacteria. As many as 29 types of microorganisms have been isolated from vaginal secretions, the most important of which is Lactobacillus. Its isolation rate in vaginal discharge samples of healthy women is as high as 50-80%. It has been determined that the microbiota colonized in the normal vagina is mainly composed of bacteria, fungi, protozoa, and viruses. They mainly reside in the folds of the vaginal mucosa, followed by the dome, and partially in the cervix. The bacteria mainly include gram-positive aerobic bacteria and facultative anaerobic bacteria, gram-negative aerobic bacteria and facultative anaerobic bacteria including Escherichia coli. Under normal conditions, the ratio of anaerobic bacteria to aerobic bacteria in the vagina is 5:1, and the two are in a dynamic equilibrium state. In addition, there are also some pathogens, such as Campylobacter, Mycoplasma, and Candida.

In the normal vaginal microbiota, lactobacilli dominate. Lactobacillus is a Gram positive macrobacterium, slightly aerobic, but grows better in anaerobic environments, with an optimal growth temperature of 35-38 ℃. Each gram of vaginal secretions contains 107-108 CFU of Lactobacillus. More than 20 types of lactobacilli can be isolated from the vagina of healthy women. The normal presence of lactobacilli in the vagina plays a crucial role in maintaining a normal vaginal microbiota. The glycogen in vaginal squamous epithelial cells is decomposed into lactic acid through the action of lactobacilli, creating a weak acidic environment in the local area of the vagina (pH ≤ 4.5, mostly between 3.8-4.4), which can inhibit the excessive growth of other parasitic bacteria. In addition, lactobacilli prevent pathogenic microorganisms from adhering to vaginal epithelial cells through substitution and competitive rejection mechanisms. At the same time, the secretion of hydrogen peroxide, bacteriocins, bacteriocins, and biosurfactants inhibits the growth of pathogenic microorganisms, thereby maintaining a balance in the vaginal microenvironment.

Interactions between hosts and microbiota, as well as between microbiota and microbiota

There is a coordinated and balanced state between the host and the microbiota, as well as between the microbiota and the microbiota. Factors such as estrogen levels, menstruation, pregnancy, and age can cause changes in the vaginal microbiota, which fluctuate within a physiological range and are beneficial for the host to adapt to the environment. After the onset of menstruation, the number of viable aerobic and facultative anaerobic bacteria continues to decrease, until it is about 100 times less than before the next menstruation, while specialized anaerobic bacteria remain unchanged. With the increase of age and the appearance of aging, the acidic environment of the vagina is destroyed, which reduces Candida albicans, Corynebacterium and Lactobacillus, and on the contrary, group B streptococcus, Staphylococcus aureus and Escherichia coli in the vagina increase.

References

Liao Qinping. Microecological Map of Female Vagina: People's Health Publishing House, 2014: 1-7

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