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Here is a complete summary of Gardnerella vaginalis / Bacterial Vaginosis (BV) - discharge characteristics, pH, and comparison with other vaginitides:
Gardnerella Vaginalis & Bacterial Vaginosis
Pathophysiology
BV results when the normal lactobacilli of the vaginal microbiota decrease in number, causing a rise in vaginal pH. This allows overgrowth of G. vaginalis and vaginal anaerobic bacteria (including curved Gram-negative rods of the genus Mobiluncus), which produce odorous amine-containing discharge. Notably, no PMN (polymorphonuclear) cells are present - hence it is a vaginosis, not a vaginitis.
Discharge Characteristics
| Feature | Detail |
|---|---|
| Appearance | Thin, homogeneous, white/grey, adherent to vaginal walls |
| Odor | Fishy (amine odor), especially after intercourse or with KOH |
| Bubbles | May be present |
| PMNs | Absent (not an inflammatory process) |
pH
- BV: > 4.5 (often 5.0-6.0)
- Normal vaginal pH: < 4.5
- The elevated pH is due to loss of lactobacilli, which normally produce lactic acid
Microscopy - Key Finding: Clue Cells
- Clue cells = vaginal epithelial cells heavily coated with Gram-variable bacilli (G. vaginalis)
- No trichomonads, no yeasts
- No PMNs
Whiff (Amine) Test
Adding 10% KOH to the discharge releases a positive fishy amine odor - this is a hallmark diagnostic test for BV.
Amsel Criteria (Diagnosis - 3 of 4 needed)
- Thin, homogeneous, grey-white discharge
- Vaginal pH > 4.5
- Positive whiff test (KOH)
- Clue cells on wet mount microscopy
Comparison Table: Vaginal Discharge Conditions
| Feature | Normal | Bacterial Vaginosis | Trichomonas vaginalis | Candida albicans |
|---|---|---|---|---|
| Discharge | Slight, white, flocculent | Thin, homogeneous, white-grey, adherent | Yellow-green, frothy; cervical petechiae | Thick, white, curdy ("cottage cheese") |
| pH | < 4.5 | > 4.5 | > 4.5 | ≤ 4.5 |
| Odor | None | Fishy (common) | May be fishy | None |
| Microscopy | Epithelial cells + lactobacilli | Clue cells; no PMNs | Motile trichomonads; many PMNs | KOH: budding yeasts + pseudohyphae |
| Treatment | None | Metronidazole (oral or topical) | Metronidazole (oral) | Topical azole antifungal |
Treatment
- Metronidazole (oral or topical) is the first-line treatment and is generally curative
- Response to metronidazole also suggests the anaerobic co-infection component
Clinical Associations
- Premature rupture of membranes
- Preterm labor and birth
- Increased susceptibility to STIs (due to disrupted normal flora)
Sources: Jawetz, Melnick & Adelberg's Medical Microbiology 28th Ed., p. 813; Goldman-Cecil Medicine
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