The vaginal surface of women is covered by a mucosal layer in which lives a microbial community called vaginal microbiota, formerly known as vaginal flora. This microbiota lives in a state of mutualistic symbiosis, so that both the organism and the microbiota itself benefit from this relationship: On the one hand, the microbiota obtains the substrate it needs to live and grow and, on the other hand, the woman’s organism benefits from the presence of these microorganisms in the vagina. This benefit consists basically in the protection of the vaginal mucosa against possible colonization by pathogenic microorganisms that can trigger important infectious conditions.
The most frequent microorganisms in the vaginal microbiota are Lactobacillus crispatus, Lactobacillus jensenii and Lactobacillus gasserii.
The vaginal microbiota of a healthy woman is made up of various types of species of microorganisms, although Lactobacilli are the most common, particularly those belonging to the genus Lactobacillus being present in a much higher proportion than the rest. Specifically, the most frequent species are: Lactobacillus crispatus, Lactobacillus jensenii and Lactobacillus gasseri although other species such as Lactobacillus acidophilus or Lactobacillus fermentum can also be identified in the vagina.
Functions of the vaginal microbiota
The microbiota plays a fundamental role in protecting the vaginal epithelium against contamination by pathogenic microorganisms. This protective mechanism is based on three mechanisms:
1) A competitive competition of the autochthonous microbiota against pathogens,
2) Production of antimicrobial substances against these undesirable microorganisms, and 3) Production of antimicrobial substances against these undesirable microorganisms.
3) Coaggregation capacity, a mechanism by which pathogenic microorganisms are surrounded by bacteria of the autochthonous vaginal microbiota, thus increasing the antimicrobial capacity.
These microorganisms that form the vaginal flora coexist with the rest of the microbiota in a situation of eubiosis or homeostasis, that is, in balance with all the species present in the vagina so that none of them is in a higher or lower proportion than it should be. Therefore, it is essential to maintain the adequate and correct level of Lactobacillus to ensure the maintenance of this homeostasis.
However, when for some reason there is a decrease in the concentration of Lactobacillus in the vagina, we enter a situation of dysbiosis in which homeostasis is broken and consequently mucosal protection decreases. The causes that can cause this decrease of Lactobacillus are diverse:
In this situation of low protection, infectious diseases caused by microorganisms or pathogens are favored, among which bacterial vaginosis, vaginitis caused by Candida species (candidiasis), trichomoniasis or urinary tract infections. It is precisely here where probiotics for women (vaginal ovules or orally administered) have a fundamental role in the recovery of the vaginal flora that has been lost due to these cases of infection.
Both vaginal ovules and oral capsules have in their composition several freeze-dried species of microorganisms of the Lactobacillus genus, as this is the major genus that needs to be repopulated.
It is important not to confuse this type of probiotics with other vaginal ovules which, although effective and indicated to reduce the pH of the vagina and lubricate its epithelium, do not contain microorganisms in their formula, i.e., they are not probiotics.
Mechanisms of protection of the vaginal microbiota against pathogenic microorganisms
We spoke at the beginning of the protective role played by the microbiota in a healthy woman, that is, when we are in a context of homeostasis and balance. There are basically three mechanisms:
1.- An adherence of lactobacilli to the vaginal epithelium forming a protective layer against pathogenic microorganisms through a process of competitive occupation.
2.- Coaggregation. Mechanism by which the pathogenic microorganism is surrounded by bacteria of the autochthonous vaginal microbiota.
3.- Production of antimicrobial substances: Basically three different types of substances are produced: Lactic acid, Hydrogen peroxide and Bacteriocins.
Lactic Acid
The pH of the vagina is predominantly acidic, around 4 which creates a hostile environment for the growth of pathogenic microorganisms. This acidity is due to the presence of lactic acid which is produced by microorganisms of the genus Lactobacillus by fermentation of glucose resulting in lactic acid.
Hydrogen Peroxide H2O2
Hydrogen peroxide has an antimicrobial effect due to its oxidizing capacity.
Some species of Lactobacillus, such as L. crispatus or L. jensenii have the capacity to synthesize hydrogen peroxide or hydrogen peroxide. These hydrogen peroxide-producing species are more stable in the vaginal environment and protect the mucosa against infections caused by pathogenic organisms, such as gonorrhea caused by Neisseria gonorrhoeae (1).
Studies have also shown that the presence of some specific species, such as L. crispatus or L. jensenii, reduce the risk of bacterial vaginosis compared to other species of hydrogen peroxide-producing bacteria(2).
Bacteriocins
Lactobacilli in the vagina also have the ability to produce bacteriocins.
Bacteriocins are toxins of protein origin with an antimicrobial function so that they inhibit the growth of other microorganisms that could be pathogenic. They act by lysing or breaking the cytoplasmic membrane of the bacterium by creating pores in it.
There are several different bacteriocins that are produced by different bacterial species and strains. Bacteriocins have a specific inhibition spectrum.
Vaginal probiotics for oral administration
Although there are vaginal probiotics in the form of vaginal ovules or suppositories for vaginal administration, there are also probiotics that, although indicated to restore the vaginal microbiota or flora, are administered orally.
This type of administration has some advantages over vaginal administration. On the one hand, when administered orally, in addition to the local action in the vagina, an intestinal action is obtained where there is also presence of Lactobacillus and where there must also be a homeostasis or eubiosis. The presence of Lactobacillus at intestinal level contributes to improve the state of the intestinal barrier, which in turn favors the correct functioning of intestinal absorption.
It also has the advantage of being a less invasive route of administration and, as it is more comfortable for the patient, it has a lower treatment abandonment rate.
References
(1)Amant DCS, Valentin-Bon IE, Jerse AE. Inhibition of Neisseria gonorrhoeae by Lactobacillus species that are commonly isolated from the female genital tract. Infection and immunity. 2002;70:7169–7171. doi: 10.1128/IAI.70.12.7169-7171.2002
(2)Antonio MA, Rabe LK, Hillier SL. Colonization of the rectum by Lactobacillus species and decreased risk of bacterial vaginosis. J Infect Dis. (2005) 192:394–8. 10.1086/430926
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