Vaginal flora, vaginal microbiota or vaginal microbiome are the
microorganisms
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
that colonize the
vagina
In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
. 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
Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as nat ...
they produce is thought to protect against infection by pathogenic species.
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''.
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
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
'', ''
Gardnerella vaginalis'',
''Mobiluncus'' spp., ''
Neisseria gonorrhoeae
''Neisseria gonorrhoeae'', also known as ''gonococcus'' (singular), or ''gonococci'' (plural), is a species of Gram-negative diplococci bacteria isolated by Albert Neisser in 1879. It causes the sexually transmitted genitourinary infection gon ...
'', ''
Peptostreptococcus anaerobius'', ''
Prevotella bivia
''Prevotella bivia'' is a species of bacteria in the genus ''Prevotella''. It is gram-negative. It is one cause of pelvic inflammatory disease.
Other ''Prevotella'' spp. are members of the oral and vaginal microbiota, and are recovered fro ...
'' and ''
Staphylococcus aureus
''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often posit ...
''. It is generally accepted that this is achieved mainly through the action of lactic acid.
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.
Next to lactic acid production and competition for adherence, other antagonistic mechanisms include
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3 ...
(a broad-spectrum antimicrobial) and
bacteriocins (target-specific antimicrobials) production.
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 .
Normal vaginal pH is considered to be under 4.5 with a range of 3.8 to 4.4.
Hydrogen peroxide
Production of hydrogen peroxide (H
2O
2) is a well-known mechanism for bacterial antagonism, inhibiting growth of microorganisms via direct interaction or via human myeloperoxidase.
Hydrogen peroxide-producing lactobacilli have been shown to inactivate
HIV-1,
herpes simplex virus type 2 (HSV-2), ''
Trichomonas vaginalis
''Trichomonas vaginalis'' is an anaerobic, flagellated protozoan parasite and the causative agent of a sexually transmitted disease called trichomoniasis. It is the most common pathogenic protozoan that infects humans in industrialized countri ...
'', ''
G. vaginalis'', ''
P. bivia'' and ''
E. coli''. O'Hanlon
and Baeten found that 96% of ''
Lactobacillus'' species from a healthy vaginal ecosystem produced H
2O
2 (''
L. jensenii'' and ''
L. vaginalis'' produce the highest levels of H
2O
2),
whereas only 6% of the lactobacilli recovered from women with BV produced H
2O
2.
In agreement with this, ''
L. iners'', most frequently associated with disturbed vaginal microflora,
is a poor producer of H
2O
2.
Vaginal colonization by H
2O
2-producing lactobacilli has been associated with a decrease in the occurrence of
bacterial vaginosis
Bacterial vaginosis (BV) is a disease of the vagina caused by excessive growth of bacteria. Common symptoms include increased vaginal discharge that often smells like fish. The discharge is usually white or gray in color. Burning with urinati ...
(BV). However, more recently O'Hanlon et al.
demonstrated that cervicovaginal fluid and semen have a significant H
2O
2-blocking activity and they later
demonstrated that physiological concentrations of H
2O
2 below 100 μM fail to inactivate any of the 17 tested BV-associated bacteria, e.g. ''
A. vaginae'', ''
G. vaginalis'',
''Mobiluncus'' spp., ''
P. bivia'', ''
P. corporis'', ''
Mycoplasma hominis'', even in the presence of human
myeloperoxidase, known to increase the microbicidal activity of H
2O
2.
Only supraphysiologic concentrations of exogenous H
2O
2 (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 H
2O
2 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 H
2O
2 concentration in vivo. Even more remarkable, the addition of only 1% vaginal fluid blocked the microbicidal activity of 1 M H
2O
2. 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 H
2O
2. 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 H
2O
2, is absent in lactobacilli,
and as such they would be unprotected against their own H
2O
2 production. In contrast, under optimal anaerobic growth conditions, physiological concentrations of lactic acid inactivated the BV-associated pathogens without affecting the vaginal lactobacilli.
In summary, although the hydrogen peroxide production of lactobacilli has been considered as an important antimicrobial component, contributing to the colonization resistance provided by lactobacilli,
and although there seems to be a link between H
2O
2-producing lactobacilli and normal vaginal microflora, recent data do not support this role for H
2O
2.
Bacteriocins
Vaginal lactobacilli produce antimicrobial peptides, i.e. bacteriocins such as lactocin 160 and crispasin.
with inhibitory activity ranging from narrow (closely related ''Lactobacillus'' species) to broad (diverse groups of bacteria, including ''
G. vaginalis'' and ''
P. bivia''),
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 ''
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 ''
L. 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.
Other microbiota
Healthy, normal vaginal microbiota that is dominated by lactobacilli may differ among some ethnic groups.
Non-pathogenic vaginal species are part of the normal microbiota of some women.
Several studies have demonstrated that a significant proportion (7–33%) of healthy asymptomatic women (especially black and Hispanic women)
lack appreciable numbers of Lactobacillus species in the vagina,
and instead have a vaginal microbiota that consist of other lactic acid-producing bacteria, i.e. species from the genera ''
Atopobium
''Atopobium'' is a genus of Actinomycetota, in the family Coriobacteriaceae. ''Atopobium'' species are anaerobic, Gram-positive rod-shaped or elliptical bacteria found as single elements or in pairs or short chains.
'' Atopobium vaginae'' was d ...
'', ''
Leptotrichia'', ''
Leuconostoc'', ''
Megasphaera'', ''
Pediococcus'', ''
Streptococcus'' and ''
Weissella
''Weissella'' is a genus of gram-positive bacteria placed within the family Lactobacillaceae, formerly considered species of the ''Leuconostoc paramesenteroides'' group. The morphology of ''Weissella'' species varies from spherical or lenticul ...
'',
All ethnic populations have vaginal microflora communities containing lactic acid producing bacteria.
This implies that not all communities may be equally resilient, so that if the resilience of a vaginal community is low then transitory changes in the structure of these communities may occur more readily in response to disturbances of various kinds, including
menses, sexual intercourse, douching and contraceptive practices. These differences in the structure and composition of microbial communities may underlie well-known differences in the susceptibility of women in these racial groups to BV and various vaginal infections.
Though vaginal microflora may be disturbed, and lactic acid is produced by other species, vaginal pH and acid production establish normal vaginal microbiota. The pH further decreases during pregnancy.
Other vaginal bacterial species
Other bacterial species are frequently found in the vagina, such as the Gram positive cocci: ''
Atopobium vaginae'',
''Peptostreptococcus'' spp.,
''Staphylococcus'' spp.,
''Streptococcus'' spp., and
''Bacteroides'' spp.,
''Fusobacterium'' spp., ''
Gardnerella vaginalis'', ''
Mobiluncus'',
''Prevotella'' spp., and
Gram-negative enteric organisms, such as ''
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
''.
''
Mycoplasma
''Mycoplasma'' is a genus of bacteria that, like the other members of the class '' Mollicutes'', lack a cell wall around their cell membranes. Peptidoglycan ( murein) is absent. This characteristic makes them naturally resistant to antibioti ...
'' and ''
Ureaplasma'' are frequently found in the vagina. Some of the obligate and facultative anaerobic bacteria are associated with BV.
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. Pregnancy alters the microbiota with a reduction in species/genus diversity.
Disease prevention
A healthy vaginal microbiome aids in the prevention of bacterial vaginosis,
yeast infections and other possible problems by maintaining an acidic pH (< 4.5) that is unfavourable for the growth of common pathogens, such as ''
Gardnerella vaginalis''. The lactobacilli present in a healthy vaginal microbiome also occupy the
ecological niche
In ecology, a niche is the match of a species to a specific environmental condition.
Three variants of ecological niche are described by
It describes how an organism or population responds to the distribution of resources and competitors (for ...
that would otherwise be available for exploitation by pathogenic organisms. However, harmful bacteria or an imbalance in bacteria can lead to infection.
Bacterial vaginosis
Bacterial vaginosis (BV) is a disease of the vagina caused by excessive growth of bacteria. Common symptoms include increased vaginal discharge that often smells like fish. The discharge is usually white or gray in color. Burning with urinati ...
is associated with the presence of ''
Gardnerella vaginalis'' and ''
Peptostreptococcus anaerobius''
and a decrease in the number of ''
Lactobacillus'' species that comprise the healthy vaginal microbiota.
Research
Investigations have found that the presence of lacto-bacillus dominated bacteria in the vagina is associated with a lower incidence of sexually transmitted infections.
See also
*
Human Microbiome Project
*
Lactic acid bacteria
*
List of microbiota species of the lower reproductive tract of women
*
Skin flora
Skin flora, also called skin microbiota, refers to microbiota ( communities of microorganisms) that reside on the skin, typically human skin.
Many of them are bacteria of which there are around 1,000 species upon human skin from nineteen phyla.P ...
*
Vaginal microbiota in pregnancy
References
External links
*
Döderlein's bacteria
{{Authority control
Bacteriology
Microbiology
Feminine hygiene
Vagina
Microbiomes