What causes bacterial vaginosis?

Causes of Bacterial Vaginosis

Bacterial vaginosis (BV) is caused by an imbalance in the normal vaginal bacterial flora, characterized by a decrease in protective Lactobacilli and an overgrowth of anaerobic bacteria including Gardnerella vaginalis, Prevotella species, Mobiluncus species, and other anaerobes. 1

Microbial Imbalance

The vaginal microbiome plays a crucial role in maintaining vaginal health. In healthy women:

• Normal vaginal flora is dominated by hydrogen peroxide-producing Lactobacillus species
• These beneficial bacteria maintain an acidic vaginal environment (pH ≤4.5)
• Lactobacilli produce lactic acid, hydrogen peroxide, and bacteriocins that inhibit pathogenic bacteria growth 1, 2

In bacterial vaginosis, this balance is disrupted:

• Protective Lactobacilli decrease significantly
• Overgrowth of anaerobic bacteria occurs, including:
  • Gardnerella vaginalis
  • Prevotella species
  • Mobiluncus species
  • Atopobium vaginae
  • Bacteroides species
  • Peptostreptococcus species
  • Mycoplasma hominis 1, 3

Risk Factors

Several factors have been associated with the development of bacterial vaginosis:

• Sexual activity: While not strictly classified as a sexually transmitted infection, BV is associated with:

  • Multiple sexual partners
  • New sexual partners
  • Frequent sexual intercourse 4, 3

• Hygiene practices:

  • Douching
  • Use of irritating feminine hygiene products
  • Vaginal deodorants 1

• Hormonal changes:

  • Menstruation
  • Pregnancy 1, 2

• Smoking: Associated with higher rates of BV 4

• Absence of protective factors:

  • Lack of hydrogen peroxide-producing Lactobacilli
  • Reduced vaginal acidity 3

Pathophysiology

The development of bacterial vaginosis involves several mechanisms:

1. Biofilm formation: Gardnerella vaginalis and other bacteria form adherent biofilms on vaginal epithelial cells 4

2. Enzymatic activity: Anaerobic bacteria produce:

   • Aminopeptidases that degrade proteins
   • Decarboxylases that convert amino acids to amines 5

3. pH elevation: The amines produced raise vaginal pH above 4.5, further inhibiting Lactobacilli growth and promoting anaerobic bacteria proliferation 5

4. Epithelial cell changes: Bacteria adhere to vaginal epithelial cells, creating characteristic "clue cells" visible on microscopic examination 5, 6

5. Altered vaginal environment: The shift in bacterial populations leads to:

   • Increased vaginal pH (>4.5)
   • Production of malodorous discharge (fishy odor)
   • Thin, homogeneous vaginal discharge 1, 6

Clinical Significance

Understanding the causes of bacterial vaginosis is important because:

• BV is associated with increased risk of:

  • Pelvic inflammatory disease
  • Post-surgical infections
  • Preterm birth and other adverse pregnancy outcomes
  • Increased susceptibility to sexually transmitted infections 1, 2

• Recurrence rates are high (50-80% within one year) after standard antibiotic treatment, suggesting that addressing underlying causes is essential for long-term management 4

• Treatment approaches target the microbial imbalance through:

  • Antibiotics (metronidazole, clindamycin, tinidazole)
  • Probiotics to restore Lactobacilli
  • pH modulation
  • Biofilm disruption 1, 7, 4

Common Pitfalls

• Misdiagnosing BV as other vaginal infections (e.g., candidiasis, trichomoniasis)
• Failing to recognize that BV is not a simple infection but a complex ecological disturbance
• Treating sexual partners, which is not routinely recommended as sexual transmission has not been definitively proven 1, 5
• Relying solely on antibiotics without addressing factors that may contribute to recurrence
• Not recognizing that approximately half of women with BV may be asymptomatic 5