Lactobacillus

Lactobacillus (Latin: Lactobacillus spp.) is a genus of Gram-positive, non-spore-forming, facultatively anaerobic or microaerophilic bacteria. They are the obligate dominant (95-98% of the total bacterial mass) of the vaginal microbiota of a healthy woman of reproductive age.

Etiology and pathophysiology

The most common species in the vaginal biotope are L. crispatus, L. jensenii, L. gasseri and L. iners. Their physiological role is to provide colonization resistance through three mechanisms:

1. Acidogenesis: Lactobacilli ferment the glycogen contained in the mature cells of the vaginal epithelium to form lactic acid. This maintains the pH of the environment between 3.8-4.5, creating unfavorable conditions for the growth of pathogenic and opportunistic microorganisms.
2. Synthesis of hydrogen peroxide (H₂O₂): Many strains produce H₂O₂, which in the presence of myeloperoxidase has a potent bactericidal effect on catalase-negative anaerobes (e.g., Gardnerella vaginalis).
3. Competitive adhesion: Bacteria densely coat receptors on the surface of epitheliocytes, forming a protective biofilm and physically preventing pathogen adhesion.

Clinical significance

Decreased titer of lactobacilli (less than 10⁶ CFU/mL) or replacement of H₂O₂-producing strains by inactive ones is a key link in the pathogenesis of bacterial vaginosis, aerobic vaginitis and candidiasis. In postmenopausal atrophic vaginitis, estrogen deficiency leads to cessation of epithelial maturation and disappearance of glycogen. This deprives lactobacilli of nutritive substrate, leads to their elimination, alkalinization of the environment and the development of dysbiosis.