Morphology and Staining Properties
Gardnerella vaginalis bacteria are very small, non-motile rods or coccobacilli measuring $1–2 \times 0.3–0.6$ \(\mu\)m. They lack flagella, capsules, and spores, but their cytoplasm may contain volutin granules.
In microscopic smears, cells may appear singly or in pairs. They frequently form clusters or arrange in palisades and the shape of the Latin letter 'V', making them morphologically similar to corynebacteria.
Gram staining is variable (gram-variable), depending on the age of the population and environmental conditions:
- In young cultures (8–12 hours), the microorganisms stain Gram-negative.
- When grown on optimal nutrient media, they appear Gram-positive.
Despite this variability, their cell wall structure is typical of Gram-positive bacteria, containing teichoic and diaminopimelic acids. The main difference from related corynebacteria is the complete absence of arabinose in the cell wall structure.
Culture and Biochemical Properties
In terms of respiration, G. vaginalis is a facultative anaerobe and capnophile (requiring an elevated $CO_2$ concentration for active growth). The optimal cultivation temperature is 35–37 °C, and the preferred environment is acidic (pH 4.5–4.0).
The microorganism is fastidious and requires complex media for cultivation, such as vaginalis agar, chocolate agar, or CDS-1 medium (supplemented with serum, casein, or yeast extract).
- On blood agar, very small colonies form with a zone of $\alpha$- or $\beta$-hemolysis, and the medium darkens over time.
- On CDS-1 medium, small, round, colorless colonies grow within 1–2 days, later becoming matte and dull.
- In liquid media, growth manifests as uniform turbidity with sediment formation.
Its metabolism is primarily fermentative. The main carbohydrate fermentation product is acetic acid; strains may also produce lactic, succinic, and formic acids. Gardnerella species can hydrolyze starch and hippurate, and ferment maltose with acid production.
A crucial diagnostic and pathogenic marker is the microbe's ability to produce volatile amines (cadaverine, putrescine, triethylamine), which cause the characteristic clinical symptom—a 'rotting fish' odor.
Epidemiology and Pathogenesis of Vaginosis
The natural ecological niche of G. vaginalis is the human urogenital tract. This bacterium is part of the normal microbiota, detected in 12–53% of healthy women and in fewer than 10% of men.
The infection is predominantly endogenous. Bacterial vaginosis is initiated when commensal bacteria shift to a pathogenic form against the background of pronounced vaginal dysbiosis. Sexual transmission is also possible, with an incubation period ranging from 3–10 days to 5 weeks, although overall susceptibility to the pathogen is considered low.
Mechanism of disease development:
- There is a sharp decrease in the number of lactobacilli, which normally maintain an acidic environment and protect the mucosa.
- Active colonization of the epithelium by Gardnerella begins, with titers reaching massive levels ($10^{10}$–$10^{12}$ CFU/mL).
- A stable pathological microbial association is formed with obligate anaerobes (such as Bacteroides, Prevotella, Mobiluncus) and Mycoplasma hominis.
The primary pathogenicity factor of G. vaginalis is the enzyme neuraminidase. It selectively degrades protective glycoproteins of the vaginal mucosa, stripping tissues of their barrier functions.
Triggers for this scenario include endocrine shifts (pregnancy, menopause, diabetes), iatrogenic factors (prolonged antibiotic, hormone, or immunosuppressant use), as well as local inflammation and stress.
Clinical Presentation and Microbiological Diagnosis
In women, gardnerellosis presents with abundant homogenous (smooth), often foamy, grayish-white discharge. Its hallmark is a sharp 'fishy' odor. Patients complain of itching, burning, perineal pain, and dyspareunia (painful intercourse).
In men, the infection is most commonly asymptomatic (forming a carrier state that is dangerous for partners), but nonspecific urethritis or balanitis may occasionally develop.
Complications include pelvic inflammatory disease (PID), and in obstetric practice, the risk of preterm birth and low birth weight. Post-infection immunity is not established.
The basis of diagnosis is the bacterioscopic method (smear microscopy). The test material includes discharge from the vagina, cervical canal, urethra, or urine. The main diagnostic criterion for vaginosis is the detection of 'clue cells'. These are squamous vaginal epithelial cells whose surfaces are so densely covered with small gram-variable flora (gardnerellae and associated anaerobes) that their borders become indistinct and their cytoplasm acquires a granular appearance.