Vaginal microecology is an ecosystem comprised of the vaginal microbiota, the host’s endocrine system, the vaginal anatomical structure, and the local immune system of the vagina. The normal vaginal microbiota is diverse and includes the following:
- Gram-positive aerobes and facultative anaerobes: Lactobacillus, Corynebacterium, non-hemolytic Streptococcus, Enterococcus, and Staphylococcus epidermidis.
- Gram-negative aerobes and facultative anaerobes: Gardnerella (which may appear as Gram-positive due to staining variability), Escherichia coli, and Morganella.
- Obligate anaerobes: Peptococcus, Peptostreptococcus, Bacteroides, Mobiluncus, Fusobacterium, and Prevotella.
- Others: Including Mycoplasma and Candida species.
Vaginal Microecological Balance and Influencing Factors
While the vaginal environment contains various microorganisms, the relationship between these microbes and the host, as well as interactions between different microbial species, is interdependent and mutually restrictive, maintaining a dynamic ecological balance that is non-pathogenic under normal conditions. Key factors in maintaining vaginal microecological balance include estrogen, local pH, lactobacilli, and the vaginal mucosal immune system.
Estrogen thickens the vaginal squamous epithelium and increases glycogen levels, which is converted into lactic acid by lactobacilli to maintain the normal acidic vaginal pH (≤4.5, typically 3.8–4.4). Additionally, estrogen supports the immune function of the vaginal mucosa, particularly T cell function. The acidic environment inhibits pathogenic microbial growth while promoting lactobacilli proliferation.
Lactobacilli producing hydrogen peroxide (H2O2) dominate the normal vaginal microbiota. In addition to sustaining the acidic environment, lactobacilli secrete H2O2, bacteriocins, and other antimicrobial factors, which inhibit or kill pathogenic microorganisms. They also prevent pathogens from attaching to vaginal epithelial cells through competitive exclusion, thereby preserving the vaginal microecological balance.
The vaginal mucosal immune system functions as both a physical barrier and an active immune defense. Immune cells and cytokines within the system play an immunoregulatory role. The main immune cells include epithelial cells, stromal fibroblasts, and lymphocytes. Vaginal secretions contain mucus with various immunomodulatory molecules, including cytokines, chemokines, and antimicrobial enzymes, all of which play an essential role in defending against vaginal infections.
When this delicate vaginal microecological balance is disrupted, it may lead to the development of vaginal infections. In populations with low estrogen levels, such as infants and postmenopausal women, vulvovaginitis in children or atrophic vaginitis may occur. A disturbed acidic environment hinders lactobacilli growth, allowing the overgrowth of anaerobic bacteria, which can cause bacterial vaginosis, or the proliferation of aerobes, resulting in aerobic vaginitis. Prolonged use of broad-spectrum antibiotics may inhibit lactobacilli growth, and excessive fungal proliferation may lead to vulvovaginal candidiasis. Invasion by exogenous pathogens such as Trichomonas vaginalis can result in trichomoniasis.
Evaluation of Vaginal Microecology and Clinical Applications
The evaluation of vaginal microecology consists of morphological and functional assessments, with morphological assessments being the primary method and functional assessments as a supplement.
Morphological Assessment
This includes microscopic examination of vaginal discharge wet mounts and Gram-stained smears. Wet mounts focus on clue cells, Trichomonas vaginalis, and leukocytes. Gram-stained smears are used for evaluating dominant bacteria, Nugent scoring, assessment of aerobic vaginitis, and the presence of Candida pseudohyphae or budding spores.
Functional Assessment
This includes the measurement of pH, H2O2, leukocyte esterase (a marker of inflammation), and sialidase (a metabolic product of anaerobic bacteria).
The vaginal microecological evaluation system plays a crucial role in the diagnosis and treatment of vaginal infections. It enables accurate diagnosis of single-pathogen infections, facilitates the detection of mixed vaginal infections, and provides valuable guidance in monitoring the restoration of the vaginal microecology following treatment.