What causes bacterial vaginosis (BV)?

Causes of Bacterial Vaginosis (BV)

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, Prevotella, Porphyromonas, Mobiluncus, and Peptostreptococcus species. 1, 2

Microbial Imbalance

BV represents a disruption of the healthy vaginal ecosystem:

• Normal vaginal flora: Dominated by hydrogen peroxide-producing Lactobacillus species that maintain vaginal acidity (pH ≤4.5) 1, 2
• BV-associated flora: Characterized by:
  • Markedly reduced or absent Lactobacillus morphology
  • Predominance of Gardnerella morphotype
  • Increased anaerobic bacteria (Prevotella bivia, Prevotella disiens, Porphyromonas spp., Mobiluncus spp., Peptostreptococcus spp.) 3, 2

Diagnostic Characteristics

BV is clinically defined by the presence of:

1. Homogeneous vaginal discharge
2. pH greater than 4.5
3. "Fishy" amine odor when vaginal fluid is mixed with 10% KOH solution (positive whiff test)
4. Presence of "clue cells" (epithelial cells covered with bacteria) on microscopic examination 1, 3

Risk Factors

Several factors have been associated with the development of BV:

• Sexual activity: Recent studies show increased risk with multiple sexual partners, though BV is not considered a classic sexually transmitted infection 2
• Disruption of vaginal flora: Use of douches, vaginal deodorants, or antibiotics that eliminate protective Lactobacilli 4
• Smoking: Associated with higher BV rates 4
• Hormonal changes: Fluctuations during menstrual cycle or pregnancy can affect vaginal flora 4
• Genetic factors: May influence susceptibility to BV 5

Pathophysiological Mechanisms

The development of BV involves several key processes:

• Loss of protective mechanisms: Reduction in hydrogen peroxide-producing Lactobacilli that normally protect against colonization by catalase-negative anaerobic bacteria 2
• Biofilm formation: BV-associated bacteria, particularly Gardnerella, can form adherent biofilms that protect bacteria from host defenses and antibiotics 4, 6
• pH elevation: Increased vaginal pH (>4.5) creates an environment favorable for anaerobic bacteria growth 1, 3
• Rectal reservoir: The rectum may serve as a reservoir for some BV-associated flora, contributing to recurrence 2

Clinical Implications

BV is associated with significant reproductive health consequences:

• Pregnancy complications: Increased risk of preterm delivery, preterm premature rupture of membranes, spontaneous abortion, and preterm labor 7
• Gynecological complications: Higher risk of pelvic inflammatory disease, postpartum endometritis, and cuff cellulitis 2, 5
• Increased susceptibility: Greater vulnerability to sexually transmitted infections, including HIV 4, 5

Treatment Challenges

BV treatment faces significant challenges:

• Standard antibiotic treatments (metronidazole, clindamycin) provide short-term cure but have high recurrence rates (50-80% within one year) 4, 6
• After antibiotic treatment, beneficial Lactobacillus species often fail to recolonize the vagina 4
• Biofilms may protect bacteria from antibiotics, contributing to treatment failures 4

Emerging Approaches

Research is exploring alternative strategies to address BV:

• Probiotics: Administration of Lactobacillus strains (particularly L. acidophilus, L. rhamnosus GR-1, and L. fermentum RC-14) shows promise in preventing recurrence 4, 8
• Vaginal microbiome transplantation: Experimental approach to restore healthy vaginal flora 4
• pH modulation: Methods to maintain acidic vaginal environment 4, 5
• Biofilm disruption: Techniques to break down protective bacterial biofilms 4

Understanding BV as a complex ecological disturbance rather than a simple infection is key to developing more effective prevention and treatment strategies.