From the Guidelines
The flora that creates the acidic environment in the vagina is primarily Lactobacillus species, especially Lactobacillus crispatus, Lactobacillus jensenii, Lactobacillus gasseri, and Lactobacillus iners. These beneficial bacteria produce lactic acid as they metabolize glycogen present in vaginal epithelial cells, which maintains the vaginal pH between 3.8 and 4.5 1. This acidic environment is crucial for vaginal health as it inhibits the growth of pathogenic organisms that could cause infections. Estrogen plays an important role in this process by promoting the thickening of the vaginal epithelium and increasing glycogen deposition, which provides the substrate for Lactobacillus metabolism. When the Lactobacillus population decreases due to factors like antibiotics, douching, or hormonal changes, the vaginal pH rises, making the environment more susceptible to infections such as bacterial vaginosis, yeast infections, or urinary tract infections. Maintaining a healthy Lactobacillus population is essential for vaginal health and can be supported through avoiding unnecessary antibiotics, not douching, and in some cases, using probiotic supplements specifically designed for vaginal health.
Some key points to consider:
- The normal vaginal flora is dominated by Lactobacillus species, which are essential for maintaining the acidic environment of the vagina 1.
- Bacterial vaginosis (BV) is a condition characterized by an imbalance in the vaginal bacterial ecosystem, with a decrease in hydrogen peroxide–producing lactobacilli and an increase in Gardnerella vaginalis, anaerobes, and mycoplasmas 1.
- The diagnosis of BV can be made using the Amsel clinical criteria or Gram stain, and treatment typically involves oral metronidazole or clindamycin, or vaginal metronidazole gel or clindamycin cream 1.
- Research has shown that maintaining a healthy Lactobacillus population is essential for vaginal health, and this can be supported through avoiding unnecessary antibiotics, not douching, and in some cases, using probiotic supplements specifically designed for vaginal health 1.
From the FDA Drug Label
NOTE: For purposes of this indication, a clinical diagnosis of bacterial vaginosis is usually defined by the presence of a homogeneous vaginal discharge that (a) has a pH of greater than 4. 5, (b) emits a “fishy” amine odor when mixed with a 10% KOH solution, and (c) contains clue cells on microscopic examination. Gram’s stain results consistent with a diagnosis of bacterial vaginosis include (a) markedly reduced or absent Lactobacillus morphology, (b) predominance of Gardnerella morphotype, and (c) absent or few white blood cells. The bacteria that create the acidic environment in the vagina are not the ones responsible, as the environment becomes less acidic (pH greater than 4.5) in the case of bacterial vaginosis.
- The normal Lactobacillus flora helps maintain the acidic environment in the vagina.
- In the case of bacterial vaginosis, there is a reduction or absence of Lactobacillus and a predominance of Gardnerella morphotype 2.
From the Research
Vaginal Microbiota and Acidic Environment
The human vagina is colonized by a diverse array of microorganisms, with Lactobacillus being the most frequently isolated microorganism from the healthy human vagina 3. The Lactobacillus species that dominate the vaginal microbiota include:
- Lactobacillus crispatus
- Lactobacillus gasseri
- Lactobacillus iners
- Lactobacillus jensenii
Creation of Acidic Environment
These vaginal lactobacilli create an acidic environment, which is thought to protect women against sexually transmitted pathogens and opportunistic infections 4. The production of lactic acid by lactobacilli is a key factor in maintaining the acidic environment of the vagina 5, 6.
Importance of Lactobacilli
Lactobacilli colonization is believed to be beneficial since it prevents other microorganisms from colonizing the vaginal epithelium via competitive adhesion, interactions with the local immunity and plasminogen-plasmin system, and the production of lactic acid, hydrogen peroxide, and antibacterial substances 6. The lactobacilli-dominated vaginal microbiome is a major determinant for female urogenital health 6.
Lactobacillus Species and Their Properties
The genus Lactobacillus is a taxonomically complex and is composed of over 170 species that cannot be easily differentiated phenotypically and often require molecular identification 7. Lactobacillus species are generally acid resistant and are able to survive ingestion, and they are generally resistant to metronidazole, aminoglycosides, and ciprofloxacin 7.