Bacterial Vaginosis: Pathogen Identification
Direct Answer
The pathogen responsible for this clinical presentation is Gardnerella vaginalis in conjunction with high concentrations of anaerobic bacteria (including Prevotella, Bacteroides, and Mobiluncus species), collectively causing bacterial vaginosis (BV). 1, 2
Diagnostic Confirmation
This patient meets the clinical diagnostic criteria for bacterial vaginosis based on the Amsel criteria, which requires three of four findings 1, 2:
- Gray, homogeneous, malodorous discharge - Present in this case 1
- Clue cells on microscopic examination - Explicitly present ("epithelial cells are studied with clue cells") 2
- Vaginal pH > 4.5 - Likely present given the clinical picture 1
- Positive whiff test (fishy odor with KOH) - The malodorous discharge suggests this 1
The absence of erythema of the vaginal wall or cervix is characteristic of BV, which is a noninflammatory condition despite being called "vaginosis" rather than "vaginitis" 1, 3.
Pathogenic Mechanism
BV results from replacement of normal hydrogen peroxide-producing Lactobacillus species with high concentrations of anaerobic bacteria and G. vaginalis. 1, 4
- G. vaginalis initiates the infection by adhering to vaginal epithelium and creating a biofilm community 5
- Symbiotic anaerobes (Prevotella, Bacteroides, Peptostreptococcus, Mobiluncus) proliferate and contribute to symptoms 1, 4
- Mycoplasma hominis is also commonly present 1, 4
Clinical Significance
The presence of clue cells is pathognomonic for BV - these are vaginal epithelial cells with bacteria adhered to their surface, creating a stippled appearance with obscured cell borders 2. This finding alone, combined with the gray malodorous discharge and absence of inflammation, confirms the diagnosis.
Important Caveats
- Culture for G. vaginalis is NOT recommended as a diagnostic tool because it lacks specificity - the organism can be present in asymptomatic women 1
- BV is associated with sexual activity (the patient's 4-year relationship is relevant), but treating the male partner does not prevent recurrence 1
- Despite barrier protection use, BV is not considered exclusively a sexually transmitted disease, though women who have never been sexually active are rarely affected 1
Treatment Indication
This symptomatic patient requires treatment with metronidazole 500 mg orally twice daily for 7 days (cure rate 95%) 2, 6, 7. The principal goal is relief of vaginal symptoms, but treatment also reduces risk of complications including pelvic inflammatory disease and post-procedural infections 2, 4.