What is exactly the human vaginal microbiota?

The vaginal microbiota or vaginal flora consists of the hundreds of bacteria and the smaller number of fungi (Candida) that populate the vagina.¹

For most women (and in contrast to the gut microbiota) the vaginal microbiota is balanced when its diversity is low (c. 200 bacterial species) and when lactobacilli – rod-shaped bacteria – predominate.¹

The vaginal microbiota is a dynamic community subject to the influence of factors that include ethnic origin, sex hormones, hormonal contraception, sexual behavior, vaginal douching, diet, smoking habits, social environment (e.g. living space) and genes.^1,3

At the same time, the vaginal flora doesn’t live alone. The anus and the entrance to the vagina are located right next to each other and intestinal bacteria from the former can colonize the latter.⁴ The gut therefore constitutes a natural reservoir of lactobacilli for the vagina, which is important for the balance of the vaginal flora^.5,6,7

How does the vaginal microbiota change throughout life?

The body evolves throughout life, and so does the vaginal microbiota. The vaginal microbiota’s composition changes greatly from childhood through adulthood to the menopause.¹ Hormonal changes alter the rhythm of our lives, and impact the vaginal microbiota as well. For example, menstruation temporarily alters vaginal microbial diversity.⁸ The microbiota also plays a role in childbirth.^1,10 During pregnancy, physiological changes occur to adapt the mother’s body to the fetus and vice versa.⁹ In pregnant woman, the vaginal microbiota is more stable, less rich and less diverse⁹, with high levels of estrogen ensuring the outright dominance of lactobacilli.^1,8 Lastly, at menopause the vaginal microbiota settles into a new balance.¹⁰

Why is the vaginal microbiota a key factor in health?

The bacteria in the vaginal microbiota help maintain a healthy vaginal environment.¹ Some of these bacteria, particularly lactobacilli, prevent pathogenic microorganisms (sidenote: Microorganisms Living organisms too small to see with the naked eye. This includes bacteria, viruses, fungi, archaea, protozoa, etc., collectively known as ’microbes’. Source: What is microbiology? Microbiology Society. ) from establishing themselves in the vagina. A number of mechanisms have been proposed:

• by producing lactic acid the microbiota promotes an acidic environment (pH ≤ 4.5) unsuitable for many pathogens^11,12
• defensive compounds produced by the microbiota, such as hydrogen peroxide (H₂O₂) or antibacterial substances (bacteriocins), attack alien bacteria, viruses and fungi^11,12
• the microbiota acts as a barrier, making it difficult for pathogens to establish themselves on the vaginal walls. The presence of lactobacilli accelerates the renewal of the epithelium, to which pathogens may try to attach themselves^11,12
• the microbiota facilitates the production by the vaginal epithelium of a protective mucus which keeps pathogens at bay^11,12
• by stimulating the woman’s immune system, the microbiota improves her ability to fight attacks by pathogens^11,12

An unbalanced vaginal microbiota: what are the associated diseases?

Stress, illness, excessive hygiene (douches), medication (antibiotic therapy, etc.), alcohol, tobacco… all of these factors can impact the composition of the vaginal microbiota.^8,13 When the composition of the microbiota is unbalanced, we have what we call a “dysbiosis (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) ”.^8,11

A vaginal dysbiosis is when lactobacilli, the key bacteria in the vaginal flora, lose their predominance, paving the way for opportunistic microorganisms to colonize the vagina.^8,11 Their presence is often associated with vaginal discharge, itching and burning, or a fishy smell, but can also be asymptomatic.⁸

A vaginal dysbiosis is associated to:

• a bacterial vaginosis, due to colonization by pathogenic bacteria¹
• a candidiasis, due to the proliferation of a fungus⁸
• reduced fertility¹¹
• a higher risk of premature birth¹

Knowing what has a direct impact on it, how can we take care of our vaginal microbiota?

Taking care of the vaginal microbiota is essential. Daily intimate hygiene is crucial to prevent dysbiosis. There’s much false information out there, so it’s important to understand the DO’S and DON’TS.

Daily:

While vaginal douching is not recommended since it alters the vaginal flora, external washing of the vulva with a suitable intimate gel¹⁵ helps reduce the unwanted accumulation of vaginal discharge, sweat, urine and fecal contaminants.¹⁶

To contribute to the good health of vaginal microbiota:

Hygiene is still necessary¹⁵, but it’s not enough. Several options for the vaginal microbiota already exist or are currently being tested:

• Probiotics: Probiotics are live microorganisms that, when administered in appropriate amounts, confer health benefits on the host.^17,18 They can reduce or safely correct microbiota imbalances. Probiotics for women administered either via the vagina or orally may help rebalance the vaginal flora, improve symptoms and reduce the risk of recurrence of various vaginal infection^13,19,20,21. This is true both for women of childbearing age and postmenopausal women.^13,20,21
• Prebiotics: Prebiotics are specific non-digestible dietary fibers that confer a health benefit. They are selectively used by beneficial microorganisms in the host’s microbiota.^22,23 When added to probiotics in specific products, they are known as symbiotics.²⁴ Prebiotics for women are thought to promote the growth of lactobacilli and to help restore healthy vaginal acidity.^19,25,26

BMI-21.12 TEST

Dysbiosis caused by a course of antibiotics can lead to Clostridioides difficile infection. This pathogen is associated with significant morbidity and mortality, as well as high health care costs worldwide. Identifying markers of this infection could contribute to improving treatment and reducing the severity of infection.

More than 1000 patients recruited from 34 European hospitals.

In this observational, prospective, multicenter study, the gut microbiota of hospitalized patients aged over 50 years was analyzed (16S rRNA sequencing combined with an oligotyping technique for identifying C. difficile) the day before starting antibiotic therapy with the aim of identifying microbial markers predictive of antibiotic-associated diarrhea (AAD) and C. difficile infection (CDI). A longitudinal analysis was also performed to assess the impact of certain antibiotics (sidenote: Penicillin + beta-lactamase inhibitor, other classes of beta-lactams, Fluoroquinolones )  on the gut microbiota.

Markers predictive of CDI

135 patients reported diarrhea in the 90 days following treatment, 15 of which had CDI. Researchers observed that the diversity of the microbiota on D1, prior to any antibiotic therapy, was lower in patients who had suffered CDI compared with those who had suffered AAD or patients who had not had diarrhea at all. The composition of their gut microbiota was also different: Enterococcus was more abundant, whereas there was a reduction in Blautia, Ruminococcus, Porphyromonas, Bifidobacteria, Odoribacter, Prevotella and Ezakiella spp. compared with patients who had not had CDI. Ruminococcus, Ezakiella and Odoribacter spp., five days prior to the onset of CDI in this cohort. These predictive markers were compared with those from a Canadian cohort of elderly patients who suffered CDI. In exactly the same way, the gut diversity was reduced; there was an increase in Enterococcus and a reduction in Ruminococcus, Ezakiella and Odoribacter spp. five days prior to the onset of infection.

Antibiotic-induced dysbiosis

The authors also found that antibiotics induced dysbiosis, which was classed as such six days after the start of treatment. The gut microbiota of patients taking beta-lactam antibiotics (a different class from penicillin) suffered the most disruption. All beta-lactams (regardless of whether they are combined with a beta-lactamase inhibitor or not) increase the abundance of Enterococcus. Treatment with penicillin combined with a beta-lactamase inhibitor was also associated with a reduction in bacteria belonging to the Clostridiales Incertae Sedis XI family, known for being associated with a reduced risk of CDI. The other classes of beta-lactams induced a reduction in bacteria belonging to Lachnospiraceae, including butyrate-producing species, known for their beneficial effects on health. Collectively, all the classes of antibiotics studied considerably altered the composition of the gut microbiota and are well documented, as they involve a high risk of developing CDI.

All women know that the hormonal fluctuations of the menstrual cycle influence, among other things, the vaginal flora and gut transit. So could female contraceptives, particularly those that work on hormones, modify, for better or worse, the dynamics of the vaginal and gut microbiota?

Oral contraceptives boost the vaginal flora...

The vaginal microbiota has a unique quality: it is in good health when its diversity is low and rod-shaped bacteria, lactobacilli, predominate. This contrasts with other microbiota, including the gut microbiota, which are considered in balance when highly diversified. The predominance of lactobacilli protects the vagina against infection, since lactobacilli release lactic acid (among other substances), which slows the proliferation of pathogens. However, where dominant lactobacilli are replaced by other types of bacteria and the vaginal flora loses its balance (dysbiosis), bacterial vaginosis can result. However, hormonal contraceptives (oral or vaginal) seem to reduce the risk of contracting this disease.¹ How? By boosting the lactobacilli! The estrogens contained in these contraceptives result in large quantities of glycogen being deposited on the vaginal walls. Glycogen is the favorite food of lactobacilli and allows the bacteria to multiply and produce more lactic acid. What about other types of contraception? Although research in this area is still limited, the vaginal ring does not seem to cause any substantial modification of the vaginal flora, while IUDs (whether copper or hormonal) appear to have no effect.¹

...but slightly disturb the gut microbiota

Unlike the vaginal microbiota, a healthy gut flora should be diverse. However, the pill artificially maintains constant levels of estrogen and progesterone in the blood, which appears to disturb the gut microbiota. In a recent study involving 16 healthy premenopausal women², oral contraceptives were associated with a minor decrease in gut microbiota diversity and differences in the abundance of several bacterial taxa. However, it is not yet known whether the hormones in the pill have a direct effect on the gut microbiota or whether they work indirectly via other physiological processes that themselves affect the bacteria in the gut. Despite this, these preliminary results show that the pill may affect women’s health. Hence the need for further studies to gain a more complete understanding of the impact of these drugs on the gut microbiota.

Delayed growth, long-term consequences on the metabolism, immunity, and cognitive development… malnutrition in children is still a global health problem, with therapeutic and food-related solutions that are still incomplete or even insufficient. Researchers have realized that the gut microbiota of these children has maturation deficits, with seemingly underdeveloped microbial communities compared to those of healthy children. The aim of this study, which steers away from the norm, is to concentrate on the gut microbiota in order to influence growth, and to see how a food supplement that targets gut microbiota (MDCF-2) improves the growth of 118 malnourished Bangladeshi children versus a pre-existing ready-to-use supplementary food (RUSF).

Children who grow and put on weight more quickly

Although RUSF has more calories, the children who received MDCF-2 gained more weight and grew more quickly. In addition, children who received MDCF-2 presented with higher levels of proteins associated with bone growth and neurological development. Another encouraging result: 21 types of bacteria that are positively linked with changes in growth were detected.

Hope for millions of children?

To date, over 30 million children under the age of five years still suffer from malnutrition world-wide. This study suggests that the healthy growth of children is inexorably linked to optimal development of their gut microbial communities after birth. Larger studies conducted in more varied geographical areas should make it possible to confirm the advantages of a nutritional therapy that targets the gut microbiota compared with traditional strategies. Confirmation of these therapeutic claims would mark a significant success in the fight against the consequences of child malnutrition.

Over 30 million children aged under 5 years suffer from moderate acute malnutrition (MAM) (sidenote: Moderate Acute Malnutrition (MAM) Defined by the World Health Organization as a weight/height ratio two to three standard deviations lower than the median of the age cohort )  world-wide. The main characteristic of this global scourge is that these children have an immature gut microbiota (GM). During a previous clinical trial (sidenote: Raman AS, Gehrig JL, Venkatesh S, et al. A sparse covarying unit that describes healthy and impaired human gut microbiota development. Science. 2019;365(6449):eaau4735. ) , the authors of this study defined a prototype food supplement (MDCF-2), which made it possible to restore the GM of children aged 12 to 18 months suffering from MAM. This new study aims to confirm the efficacy of MDCF-2 in children suffering from MAM in a larger study conducted over a longer period of time.

An interventional study conducted on 123 Bangladeshi children

In this randomized, controlled trial, 123 Bangladeshi children (12 to 18 months old) suffering from MAM received either MDCF-2 supplementation (204 kcal per daily dose of 50 g), or an existing ready-to-use supplementary food (RUSF, 247 kcal per daily dose of 50 g) twice a day for three months, followed by a one-month follow-up. At the same time, the team of researchers monitored weight, height, and arm circumference on a weekly basis, and also took blood and stool samples regularly.

Faster growth, more weight gain

Of the 118 children who completed the study (59 in each group), those in the MDCF-2 group had grown more rapidly than those in the RUSF group. For the children in the MDCF-2 group, the mean weekly variation in the weight-for-height index was 0.021, versus 0.010 in the RUSF group. As for weight-for-age, the mean weekly variation was 0.017 in the MDCF-2 group and 0.010 in the RUSF group. The variations in arm circumference and height-for-age index were similar in both groups.

Blood and intestinal biomarkers identified

After supplementation with MDCF-2, 714 proteins were significantly modified, versus 82 in the RUSF group. Although some of them were associated with musculoskeletal and nervous system development (p<0.001), 70 were also correlated with the weight-for-height index. On the other hand, proinflammatory markers, accentuated by malnutrition at the start of the study, were more largely reduced by MDCF-2 supplementation. With regard to the microbiota, MDCF-2 supplementation made it possible to significantly increase 21 bacterial taxa positively associated with the weight-for-height index (p<0.001) and inversely, to reduce two bacterial taxa (Escherichia coli and a species of Bifidobacterium) negatively associated with the weight-for-height index (p<0.001).

This study backs the following statement: adequate calorie and nutritional supply is insufficient for remedying the consequences of long-term malnutrition. According to the authors, optimal maturation of the GM is a priority. In order to evaluate the efficacy of this new therapeutic approach, larger studies are needed, which should be conducted in different geographical locations and in a broader pediatric age bracket.

We all know how vegetables are good for us when it comes to nutrition, digestion, hydration, and reducing stress, but with this new discovery their benefits seem endless: the winning combination of nitrates and their effects on our oral bacteria. Like many other vegetables, beetroot is rich in inorganic nitrate, which is transformed by the oral bacteria into nitrite and then nitric oxide (NO). NO is beneficial to the health of our arteries and our grey matter. The only problem is that NO production diminishes with age. Could a glass of nitrate-rich beetroot juice help roll back the years?

Ten days of nitrate-rich beetroot juice for an oral microbiota in top form

This supplementation has fast-acting effects: a study has shown that consuming beetroot juice for ten days was enough to considerably modify the oral microbiota of about thirty Icelanders aged 70-80. Consuming the nitrate-rich juice influenced a number of bacterial groups in their oral microbiota. Specifically, there was a decrease in certain bacteria associated with inflammation (Prevotella and Veillonella) and in the dreaded Clostridium difficile, which can infect the gut and cause diarrhea. Conversely, other bacteria became relatively more abundant, such as a group comprising Neisseria and Haemophilus, both of which are associated with periodontal health, younger age, lower BMI, and abstinence from smoking.

Blood pressure down, attention up, morale excellent

Nitrate supplementation via beetroot juice reduced average blood pressure in participants. High blood pressure is a risk factor for cognitive decline. In this study, a reduction in blood pressure went hand in hand with an increase in certain bacteria (Streptococcus and Rothia) whose presence increases following absorption of the juice. Moreover, nitrate-rich beetroot juice also proved beneficial to cognitive health. However, the participants in the study were active and healthy seniors whose blood pressure was generally good. It remains to be seen whether this beneficial effect can be reproduced in other age groups and in people in poorer health. In the meantime, we should all include as many vegetables as possible in our meals and smoothies!

Sources

^{Vanhatalo A, L'Heureux JE, Kelly J et al. Network analysis of nitrate-sensitive oral microbiome reveals interactions with cognitive function and cardiovascular health across dietary interventions. Redox Biol. 2021 Mar 5;41:101933.}

Endometriosis (EMS) is an inflammatory disease characterized by the presence of endometrial tissue outside the uterine cavity. Different studies suggest a prevalence for the disease of between 6% and 15% for women of reproductive age. EMS can cause severe primary dysmenorrhea, reduced infertility, and pelvic mass, seriously affecting women’s quality of life. The pathogenesis of EMS is still poorly understood, but the microbiota may be involved. Certain hypotheses blame inflammatory endotoxins found in the peritoneal cavity, such as bacterial lipopolysaccharide (LPS). These inflammatory endotoxins could regulate the pro-inflammatory reaction and promote the growth of endometriosis.¹

Vaginal lactobacillus diminished

To further investigate the “bacterial contamination hypothesis”, a team collected microbiota samples from along the reproductive tracts of 36 women with endometriosis and 14 controls who had undergone surgery for a benign gynecological tumor. The results? An increasingly pronounced dysbiosis as one moves up the reproductive tract, a decrease in Lactobacillus in the vaginal flora which becomes more pronounced as one moves up towards the endometrium, and specific OTUs (sidenote: Operational Taxonomic Unit groups of organisms usually not cultivated or not identified, classified on the basis of the similarity of the DNA sequencing of a given gene. Frequently used as an equivalent to the concept of species )  in the cervical mucus which increase in the upper genital tract (endometrial samples and peritoneal fluid). This alteration of the microbiota all along the reproductive tract suggests that certain bacteria may be involved in the pathogenesis of EMS.

Role of the gut microbiota?

EMS is far from being limited to gynecological symptoms: up to 90% of patients report gastrointestinal symptoms as well.² Two studies, one in Sweden² (66 EMS patients, 198 matched controls) and the other in Shanghai³ (12 EMS patients with moderate to severe forms of the disease, 12 controls), examined the link between the gut microbiota and EMS: the alpha (sidenote: Beta diversity Rate of variation in species composition, calculated by comparing the number of unique taxa in each ecosystem ) , and to a lesser extent beta (sidenote: Beta diversity Rate of variation in species composition, calculated by comparing the number of unique taxa in each ecosystem ) , diversity of the EMS patients’ flora was found to be lower than that of the controls. In addition, the abundance of bacterial taxa differed. In the Chinese study, Prevotella was dominant among the EMS patients, while Coprococcus prevailed among the controls. Additionally, the gut microbiota of the EMS group was enriched for certain microbial function categories (environmental information processing, endocrine system, and immune system). Serum levels of hormones (particularly estradiol) and inflammatory factors (notably IL-8) were significantly higher in the women with EMS.³ Lastly, correlations were detected between the abundance of both Blautia and Dorea and estradiol level, and between Subdoligranulum abundance and IL-8 level.³ Thus, there are associations between the gut microbiota and both serum hormones and inflammatory factors in EMS.

Estrogen or inflammatory etiology?

EMS is an estrogen-dependent disease² and EMS patients generally have high estrogen levels in the serum.³ The gut microbiota, including Ruminococcaceae and Clostridia, may affect estrogen levels in the serum by modulating the reabsorption of estrogen excreted in the bile which eventually enters the gut.³ Other authors suggest a regulatory role for the gut microbiota in inflammatory processes outside the gastrointestinal tract.² In other words, although correlations have been observed and hypotheses suggested, the actual mechanisms involved have not yet been elucidated. Nevertheless, these three studies highlight the involvement of the microbiota of the reproductive and digestive tracts in EMS, giving hope for an improvement in the diagnosis and management of the disease.

Colonization of the gut microbiota begins at birth through contact with the microorganisms in the mother’s vaginal flora (in the case of vaginal delivery) or microbes on the mother’s skin and in the environment (in the case of caesarean section). According to various studies, it then evolves steadily towards a stable adult-like composition 2-3 years after birth. But has the gut microbiota really reached maturity at this stage? A team of Swedish researchers studied the dynamics of the gut microbiota’s development during the first 5 years of life in a birth cohort of 471 infants (302 born vaginally, 169 via C-section). The infants’ gut microbiota was profiled via the 16S rRNA gene sequencing of fecal samples collected during their first week of life, at 4 and 12 months, and at 3 and 5 years. It was then compared to that of the infants’ mothers and that of healthy adults. The main finding was that the alpha diversity (of species) in the children’s stool, which indicates the richness of their gut microbiota, was still lower than that of adults at 5 years of age.

Maturation in stages throughout childhood

By measuring the prevalence and proportion of the main taxa at each age studied, the authors were able to observe that the gut microbiota developed at different speeds in different children but along relatively similar trajectories. Gut microbiota composition changes the most between 4 and 12 months, at the time of food diversification. There is major colonization by Ruminococcus gnavus, whose relative abundance decreases progressively from 12 months. Archaea such as Methanobrevibacter and bacteria belonging to the Christensenellaceae family, typical of the adult gut microbiome, appear first at 12 months and continue to increase in abundance between the ages of 3 and 5. This dynamic seems essential to the maturation of the gut microbiota: the more diversified the child’s gut microbiota, the more abundant these late colonizers and the lower the proportion of R. gnavus. Both low gut microbiota richness and high proportions of R. gnavus have been repeatedly linked by studies to illnesses such as metabolic syndrome, cardiovascular disease, and inflammatory bowel disease, while an increased abundance of Methanobrevibacter and Christensenella, among others, has been linked to metabolic health and a lower body mass index.

A balance to be protected from disturbances

This study was widely reported in the press and although the authors have not made any recommendations at this stage, they emphasize that the gut microbiota is likely to be extremely sensitive to disturbances during its development, with such disturbances having profound effects on health. However, some of their findings on the impact of early factors on the development of the gut microbiota are surprising. For example, antibiotic use during pregnancy or in the infant’s first year of life does not affect gut microbiota diversity over time. Moreover, mode of birth seems to play a limited role: gut microbiota diversity in children born by C-section is certainly lower at 4 months than in children born vaginally, but this normalizes by the age of 3. Therefore, we should ensure optimal development of the gut microbiota at very least beyond the age of 5 to give children every chance of a healthy future.

It is an undisputed scientific fact that babies in the womb have no gut microbiota: their digestive system is sterile. The microbiota begins to develop from birth through contact with the microorganisms present in the mother’s body during delivery and through contact with the environment. The microbiota gradually becomes stronger and richer in “friendly” bacteria and comes to resemble that of an adult by the time the child is 2 or 3 years old–or so, scientists thought until now. Recently, some research teams have shown that this process may take longer, a finding now supported by a Swedish study which followed more than 470 children from birth to 5 years of age.

Gut microbiota “adult” at age 5? Not quite!

The researchers analyzed the microorganisms present in children’s stool at different ages (at birth, at 4 and 12 months, and at 3 and 5 years) and compared them to samples taken from their mothers and other adults. They began by looking at diversity in the samples. Their first finding was that only a very small minority (3.5%) of the 5 year olds had a gut microbiota as mature as that of the adults.

They subsequently observed how these microorganisms colonized the gut. Roughly speaking, from birth to 4 months, the gut microbiota contains mainly lactic acid bacteria and Bifidobacterium. From 4 months to 1 year, dietary diversification results in a great upheaval: many new microorganisms arrive and settle in, with some microbes multiplying and others becoming less abundant. Between the ages of 1 and 3, this small community develops towards a more “adult” gut microbiota. However, some microorganisms known to be essential for health do not appear until 1 year of age and continue to increase in abundance beyond 3 years of age. Even at 5 years, these microorganisms are still short of adult levels.

For better health, protect the microbiota’s development

The authors of the study stress that the gut microbiota is sensitive to disturbances throughout its development. It is now also known that a gut microbiota imbalance (dysbiosis) in infancy (e.g. due to antibiotic use) can have health repercussions later in life: digestive disorders, excess weight, allergies^2,3,4, etc. We also know that a healthy diet during food diversification helps build a healthy gut microbiota.⁵ Therefore, we should ensure optimal development of the gut microbiota at very least beyond the age of 5 in order to give children every chance of a healthy future.