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Vaginal flora, vaginal microbiota or vaginal microbiome are the microorganisms that colonize the vagina. They were discovered by the German gynecologist Albert Döderlein in 1892 and are part of the overall human flora. The amount and type of bacteria present have significant implications for an individual's overall health. The primary colonizing bacteria of a healthy individual are of the genus Lactobacillus, such as L. crispatus, and the lactic acid they produce is thought to protect against infection by pathogenic species.
Next to lactic acid production and competition for adherence, other antagonistic mechanisms include hydrogen peroxide (a broad-spectrum antimicrobial) and (target-specific antimicrobials) production.
Experimentally, hydrogen peroxide-producing lactobacilli have been shown to inactivate HIV, herpes simplex virus type 2 (HSV-2), Trichomonas vaginalis, G. vaginalis, Prevotella bivia and Escherichia coli. O'Hanlon and Baeten found that 96% of Lactobacillus species from a healthy vaginal ecosystem produced H2O2 ( L. jensenii and L. vaginalis produce the highest levels of H2O2), whereas only 6% of the lactobacilli recovered from women with BV produced H2O2. In agreement with this, L. iners, most frequently associated with disturbed vaginal microflora, is a poor producer of H2O2. Vaginal colonization by H2O2-producing lactobacilli has been associated with a decrease in the occurrence of bacterial vaginosis (BV). However, more recently O'Hanlon et al. demonstrated that cervicovaginal fluid and semen have a significant H2O2-blocking activity and they later demonstrated that physiological concentrations of H2O2 below 100 μM fail to inactivate any of the 17 tested BV-associated bacteria, e.g. A. vaginae, G. vaginalis, Mobiluncus, Prevotella bivia, Prevotella, Mycoplasma hominis, even in the presence of human myeloperoxidase, known to increase the microbicidal activity of H2O2. Only supraphysiologic concentrations of exogenous H2O2 (0.34% w/v, 100 mM) were sufficient to inactivate BV-associated bacteria at which concentration it more potently inactivated vaginal lactobacilli ( L. crispatus, L. gasseri, L. iners and L. jensenii). A concentration of 100 mM H2O2 is approximately 50-fold higher than lactobacilli are capable of producing even under optimal aerobic, low-antioxidant conditions, and approximately 5,000-fold higher than the estimated H2O2 concentration in vivo. Even more remarkable, the addition of only 1% vaginal fluid blocked the microbicidal activity of 1 M H2O2. Possible explanations may be that cervicovaginal fluid and semen contain proteins, glycoproteins, polysaccharides, lipids, and other molecules with the potential to react with and inactivate H2O2. In addition, the vagina is hypoxic most of the time, whereas lactobacilli require oxygen to produce hydrogen peroxide. It is also remarkable that catalase, which provides bacteria protection against toxic H2O2, is absent in lactobacilli, and as such they would be unprotected against their own H2O2 production. Consequently, hydrogen peroxide production may not be the major mechanism of defense.
The inhibitory substances produced by vaginal Lactobacillus is a primary factor in protecting the vaginal microbiota, with organic acids, bacteriocins, and hydrogen peroxide. These act synergistically against infection by pathogens. Not all Lactobacillus spp. and not all strains within one Lactobacillus species exhibit all 3 mechanisms. Lactobacillus species differ in premenopausal women, i.e. L. crispatus, L. jensenii, L. iners, L. gasseri (and possibly Limosilactobacillus vaginalis), as assessed through cultivation-dependent and cultivation-independent techniques. Vaginal lactobacilli have been shown to display a pronounced vaginotropism, and their pili act as ligands for attachment to receptors of vaginal epithelial cells. The limited number of Lactobacillus spp. found in the human vagina is remarkable, which leads to the possibility that there are host factors that select for specific organisms, that these species have unusual characteristics that allow them to successfully colonize the vagina, or both . However, the vaginotropism, does not only apply to this selected group of lactobacilli that stand for a healthy vagina, but also for the bacterial species associated with BV. The microbiota detected in the human genital and gut econiche do not appear to grow outside their host and probably are likely to rely on the close contact between parents and their children for transmission, e.g. mother to neonate transmission of genital microflora, most probably also with gut microflora homogenously distributed over the baby's body including skin, the oral cavity, nasopharynx, and feces.
Typically, only women with symptoms receive treatment. Treatments include antibiotics, specifically metronidazole and clindamycin (Hay, 2010). As rates of recurrence are high, women may also turn to treatments such as Probiotic or boric acid suppositories. Boric acid has been used to treat BV since the 1800s. Yet due to the compound's role in killing pests, the prescription of boric acid by healthcare providers to treat BV may be met with dissatisfaction; science journalist Rachel E. Gross was inspired to write the book Vagina Obscura after receiving 'what was "basically rat poison"' from her gynecologist and accidentally ingesting it midway through her course of treatment, which led her to consider the extent of the medical establishment's neglect of women's health.
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.
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. Smoking and alcohol consumption can also increase likelihood of BV development because it indirectly impacts the metabolite production profile. 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.
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.
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