The vaginal surface is covered by a layer of mucous in which a microbial community called vaginal flora or vaginal microbiota lives. 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 be able 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 basically consists in the protection of the vaginal mucosa against the possible colonization by pathogenic microorganisms that can trigger important infectious conditions.
The vaginal microbiota of a healthy woman is made up of various types of microorganism species, although it is the genus Lactobacillus that is present in a much higher proportion than the rest. Specifically, the most common 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 vaginal microbiota plays a fundamental role in protecting the vaginal epithelium from contamination by pathogenic microorganisms. This protection mechanism is based on three mechanisms: 1) A competitive competition of the native microbiota against pathogens, 2) Production of antimicrobial substances against these undesirable microorganisms and 3) A capacity of coaggregation of pathogenic species to increase the antimicrobial capacity.
These microorganisms that form the vaginal flora live together with the rest of the microbiota in a situation of eubiosis or homeostasis, that is, in a balance between all the species present in the vagina so that none of them is in a greater or lesser proportion than it should be. It is therefore essential to maintain the right and adequate 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 the homeostasis is broken and therefore the protection of the mucosa is reduced. The causes that can cause this decrease in Lactobacillus are diverse:
- A woman’s hormonal situation depending on where she is in her menstrual cycle.
- An increase in pH that may be due to menstrual discharge, contact with semen as well as the use of tampons. The adequate pH of the vagina is acidic, it is around 4, since at this pH the growth of pathogenic microorganisms is inhibited. For this reason, an increase in pH values can trigger the growth of undesirable microorganisms and lead to infectious conditions.
- Use of spermicides since these inhibit the growth of lactobacillus.
- Treatment with antibiotics in bacterial infections.
- Treatment with antineoplastics.
In this situation of low protection, infections produced by microorganisms or pathogenic agents are favored, among which bacterial vaginosis, vaginitis by species of the genus Candida (candidiasis), trichomoniasis or urinary tract infections stand out. It is precisely here that vaginal probiotics (vaginal or orally administered vaginal suppositories) play a fundamental role in the recovery of lost vaginal flora.
Both vaginal suppositories and oral capsules have in their composition several freeze-dried species of microorganisms of the genus Lactobacillus, as this is the majority 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 for women’s pH balance of the vagina and lubricating 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 were talking at the beginning about the protective role that the microbe plays in a healthy woman, that is, when we are in a homeostasis context and in balance. These mechanisms are basically three:
1.- An adhesion of the 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 from the native vaginal microbiota.
3.- Production of antimicrobial substances: Basically, three different types of substances are produced: Lactic acid, hydrogen peroxide and bacteriocins.
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 ability 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 gonorrhoea caused by Neisseria gonorrhoeae(1).
Studies have also shown that the presence of certain specific species such as L. crispatus or L. jensenii reduces the risk of suffering from bacterial vaginosis compared to other species of hydrogen peroxide producing bacteria(2)
The 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 become pathogenic. They act by lysing or breaking down the cytoplasmic membrane of the bacteria by creating pores in it.
There are several different bacteriocins that are produced by different bacterial species. Bacteriocins have a specific inhibition spectrum.
Vaginal probiotics for women – oral administration vs vaginal route
Although there are vaginal probiotics in the form of suppositories for administration via the vagina, there are also probiotics which, although indicated to restore the microbiota or vaginal flora, are administered orally.
This type of administration has some advantages over the vaginal route. 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 the presence of Lactobacillus and where there must also be a homeostasis or eubiosis. The presence of Lactobacillus at an intestinal level contributes to improving 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 rate of abandonment of the treatment.
(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
Degree in Pharmacy and Specialist in Clinical Analysis from the Complutense University of Madrid.
Technical Director and Consultant at Laboratorio López Salcedo.
Director of the Institute of Microecology – study of intestinal and vaginal microbiota.
Specialist in Clinical Genetics by the Hospital Ramón y Cajal of Madrid
University Specialist in Clinical Occupational and Applied Biopathology
Diploma in Advanced Studies from the UNESCO Chair in Bioethics and Biojuridical