Gardnerella vaginalis

Morphology and staining properties

Bacteria of the species Gardnerella vaginalis are very small, non-motile rods or coccobacilli measuring $1–2 \times 0.3–0.6$ \u00b5m. They lack flagella and capsules and are incapable of forming spores, although inclusions—volutin granules—can be found in their cytoplasm.

In a microscopic smear, cells can be located individually or in pairs. They often form clusters or arrange themselves in palisades and the shape of the Latin letter "V", making them morphologically similar to corynebacteria.

Gram staining is unstable (Gram-variability), which depends on the age of the population and environmental conditions:

• In young cultures (8–12 hours), microorganisms stain Gram-negatively.
• When grown on optimal nutrient media, they become Gram-positive.

Despite this variability, the structure of their cell wall is typical of Gram-positive bacteria: it contains teichoic and diaminopimelic acids. The main difference from related corynebacteria is the complete absence of arabinose in the cell wall structure.

Cultural and biochemical properties

By type of respiration, gardnerellae are facultative anaerobes and capnophiles (they require an elevated $CO_2$ concentration for active growth). The optimal cultivation temperature is 35–37 \u00b0C, and the preferred medium is acidic (pH 4.5–4.0).

The microorganism is quite fastidious regarding nutrition. Complex media are used for its cultivation: vaginalis agar, chocolate agar, and CDS-1 (supplemented with serum, casein, or yeast).

• On blood agar, very small colonies form with a zone of $\alpha$- or $\beta$-hemolysis, and the medium itself eventually acquires a dark "chocolate" shade.
• On CDS-1, after 1–2 days, small, round, colorless colonies grow, which become matte and dull as they enlarge.
• In liquid media, growth manifests as uniform turbidity with sediment formation.

The metabolism of the bacterium is fermentative in nature. The main product of carbohydrate fermentation is acetic acid; strains may also produce lactic, succinic, and formic acids. Gardnerellae are capable of hydrolyzing starch and hippurate, and breaking down maltose with acid production.

A crucial diagnostic and pathogenetic marker is the microbe's ability to produce volatile amines (cadaverine, putrescine, triethylamine), which cause the characteristic clinical symptom—the "rotten fish" odor.

Epidemiology and pathogenesis of gardnerellosis

The natural ecological niche of G. vaginalis is the human urogenital tract. This bacterium is part of the normal microflora: it is detected in 12–53% of healthy women and less than 10% of men.

The infection is predominantly endogenous in nature. Bacterial vaginosis starts when the commensal bacterium transitions into a pathogenic form against the background of pronounced vaginal dysbiosis. Sexual transmission is also possible, with the incubation period varying from 3–10 days to 5 weeks, although overall susceptibility to the pathogen is considered low.

Mechanism of disease development:

1. There is a sharp decrease in the number of lactobacilli, which normally maintain an acidic environment and protect the mucosa.
2. Active colonization of the epithelium by gardnerellae begins—their titer can reach gigantic values ($10^{10}$–$10^{12}$ CFU/ml).
3. A stable pathological microbial association is formed with obligate anaerobes (such as Bacteroides, Prevotella, Mobiluncus) and Mycoplasma hominis.

The main pathogenicity factor of gardnerella is the enzyme neuraminidase. It specifically destroys the protective glycoproteins of the vaginal mucosa, depriving the tissues of barrier functions.

Triggers for this scenario include endocrine shifts (pregnancy, menopause, diabetes), iatrogenic factors (prolonged use of antibiotics, hormones, immunosuppressants), as well as local inflammation and stress.

Clinical presentation and microbiological diagnostics

In women, gardnerellosis manifests as copious, homogenous (without lumps), often foamy grayish-white discharge. Its hallmark is a pungent "fishy" odor. Patients complain of itching, burning, perineal pain, and dyspareunia (pain during intercourse).

In men, the infection is most often asymptomatic (forming carriage status, which is dangerous for the partner), but nonspecific urethritis or balanitis may sometimes develop.

Complications of the infection include pelvic inflammatory disease (PID), and in obstetric practice, the risk of preterm birth and fetal growth restriction. Post-infection immunity is not formed after the disease.

The basis of diagnostics is the bacterioscopic method (smear microscopy). The material for study is discharge from the vagina, cervical canal, urethra, or urine. The main diagnostic criterion for vaginosis is the detection of "clue cells". These are stratified squamous vaginal epithelial cells whose surface is so densely covered with fine Gram-variable flora (gardnerellae and associated anaerobes) that their edges become blurred and the cytoplasm acquires a granular appearance.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Biochemical classification: division of the species into 6 biotypes.
• Antigenic structure: 7 serogroups and shared antigens with fungi of the genus Candida.
• Features of the synergism of gardnerellae with obligate anaerobes (Bacteroides, Mobiluncus).
• Mechanism of action of bacterial neuraminidase on the vaginal mucosa.
• Differential diagnosis with true corynebacteria (absence of arabinose).

Other topics in the section "Irregular Gram-positive rods (Diphtheria, Mycobacteria/tuberculosis and leprosy, Actinomycetes, Nocardia, Bifidobacteria, Gardnerella, etc.)"

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