Vaginal flora
Vaginal flora, vaginal microbiota or vaginal microbiome are the
Lactobacilli
The primary colonizing bacteria of a healthy individual are of the genus Lactobacillus (90–95%), the most common being L. crispatus, L. iners, L. jensenii, and L. gasseri.[5] Since the first description of lactobacilli by Döderlein, lactobacilli have been generally considered the gatekeepers of the vaginal ecosystem. Lactobacilli have been shown to inhibit in vitro growth of pathogenic microorganisms, e.g. Bacteroides fragilis, Escherichia coli, Gardnerella vaginalis, Mobiluncus spp., Neisseria gonorrhoeae, Peptostreptococcus anaerobius, Prevotella bivia and Staphylococcus aureus. It is generally accepted that this is achieved mainly through the action of lactic acid.[6][7][8][9] Moreover, lactobacilli normally help to prevent long-term colonization of the vagina by adhering to vaginal epithelial cells. This usually reduces pathogens from infecting to the vaginal epithelium.[10]
Next to lactic acid production and competition for adherence, other antagonistic mechanisms include hydrogen peroxide (a broad-spectrum antimicrobial) and bacteriocins (target-specific antimicrobials) production.[11][12]
pH and lactic acid
Low pH is generally accepted to be the main mechanism controlling the composition of the vaginal microflora. Although the lactic acid produced by lactobacilli contributes to the vaginal acidity, it is still not proven to be the primary source of low vaginal pH, but the fact remains that most lactobacilli thrive best at a pH < 3.5 .[13][14][15] Normal vaginal pH is considered to be under 4.5 with a range of 3.8 to 4.4.[5]
Hydrogen peroxide
Production of hydrogen peroxide (H2O2) is a well-known mechanism for bacterial antagonism,
Bacteriocins
Vaginal lactobacilli produce antimicrobial peptides, i.e. bacteriocins such as lactocin 160 and crispasin.[13] with inhibitory activity ranging from narrow (closely related Lactobacillus species) to broad (diverse groups of bacteria, including G. vaginalis and P. bivia),[8] and bacteriocin-like substances, with a broader spectrum of activity than bacteriocins (e.g. a heat-resistant peptide produced by Ligilactobacillus salivarius subsp. salivarius CRL 1328). Several studies have indicated that the activity of bacteriocins is favored by low pH.
The inhibitory substances produced by vaginal
Bacteria vaginosis
Bacterial vaginosis (BV) is associated with the presence of Gardnerella vaginalis and Peptostreptococcus anaerobius[36] and a decrease in the number of Lactobacillus species that comprise the healthy vaginal microbiota.[37][38][39][40] BV is characterized by overgrowth of opportunistic bacteria and a decrease in Lactobacillus species. BV can present itself as symptomatic or asymptomatic. Symptoms include vaginal malodor, increased vaginal pH, and vaginal itching. [41] There is no one known cause as to why BV occurs but it is typically associated with abnormal vaginal discharge (Coudray & Madhivanan, 2020). To diagnose BV in a clinical setting, an Amsel's criteria is used. This means that a patient must have an increased homogeneous thin vaginal discharge, pH secretion higher than 4.5, amine odor when secretions are exposed to hydroxide 10% solution, or clue cells visible on a wet mount. Another way to diagnose BV that is less often used in a clinical setting is a Nugent score. To obtain a Nugent score, gram stain techniques are carried out and it characterizes the bacterial morphology on a scale. A score greater than 7 is associated with BV, 4-6 is an intermediate abnormality, and 0-3 is normal.[42] Typically, only women with symptoms receive treatment. Treatment include antibiotics, specifically metronidazole and clindamycin (Hay, 2010).
Studies have shown a correlation between vaginal microbiota and BV development through 16S RNA sequencing. Community state types (CSTs) are used to identify variation between a healthy vaginal microbiota and vaginal microbiota of someone with BV. Most CSTs in a healthy vaginal microbiome consist of different species of Lactobacillus. Studies found that L.iners is the dominant species in BV and L.crispatus is the dominant species in healthy vaginal microbiomes.[43]
Other microbiota
Healthy, normal vaginal microbiota that is dominated by lactobacilli may differ among some ethnic groups.
Other vaginal bacterial species
Other bacterial species are frequently found in the vagina, such as the Gram positive cocci:
Pregnancy
The effect of tampon use on vaginal flora is debated, but application of tampons appears not to significantly modify the balance of bacterial presence.[51] Pregnancy alters the microbiota with a reduction in species/genus diversity.[37]
Disease prevention
A healthy vaginal microbiome aids in the prevention of bacterial vaginosis,
There are many factors that contribute to the composition of vaginal microbiota including stress, age, lifestyle, diet, gut microbiota, antibiotics, probiotics, and vaginal infections.
Lifestyle can impact microbiota by means of personal hygiene. Research suggests that vaginal douching is associated with increased risk of BV. It also shows that sexual practices that include multiple sexual partners can increase BV or throw off stable microbiota composition.[53] Smoking and alcohol consumption can also increase likelihood of BV development because it indirectly impacts the metabolite production profile.[54] There is also research supporting the idea that increased stress levels can have an impact on the balance of vaginal lactobacilli by elevating cortisol levels, reducing vaginal glycogen, lowering lactobacilli, elevating vaginal pH, and increasing proinflammatory response.[53]
It is becoming more commonly known how our diets can impact our gut microbiota, but it can have the same impact on vaginal microbiota. Research shows that diets rich in nutrients with low glycemic index and lower fat intake may be associated with a decreased chance of getting BV.[53]
Research
Investigations have found that the presence of lactobacilli in the vagina is associated with a lower incidence of sexually transmitted infections.[55][56]
See also
- Human Microbiome Project
- Lactic acid bacteria
- List of microbiota species of the lower reproductive tract of women
- Skin flora
- Vaginal microbiota in pregnancy
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External links
- Media related to Vaginal flora at Wikimedia Commons
- Döderlein's bacteria