Vaginal Microbiota and the Use of Probiotics
The human vagina is inhabited by microbes of over 50 species.
Lactobacilli are the most common vaginal microbes, particularly in healthy women.
Vaginal microbiome is less complex than the microbiome of the gut.
The microbiota can change rapidly leading to infection or to a state in which organisms with pathogenic potential coexist with other commensals.
The most common urogenital infection in premenopausal women is bacterial vaginosis, characterized by a depletion of lactobacilli population and the presence of Gram-negative anaerobes, or in some cases Gram-positive cocci, and aerobic pathogens.
Bacterial vaginosis is characterized by anaerobic species with predominance over typical lactobacilli.
Treatment of bacterial vaginosis traditionally involves the antibiotics metronidazole or clindamycin.
Recurrence rate remains high for bacterial vaginosis.
In vitro studies have shown that Lactobacillus strains can disrupt bacterial vaginosis and yeast biofilms and inhibit the growth of urogenital pathogens.
The microbial species in the vaginal tract play an important role in the maintenance of health, and prevention of infection.
In women, differences are noted in the composition of resident microorganisms soon after birth as well as at prepubertal, postpubertal, and postmenopausal transitions.
At puberty, anaerobic and aerobic lactobacilli aid in maintaining vaginal pH.
If the normal microbiota is suppressed, it allows for yeast and other bacteria to grow causing vaginitis, and dramatic shifts in the makeup of the vaginal microbiota can lead
There are more than 50 microbial species in the vaginal tract., while in comparison, the gut is populated with more than 800 species of microbes, the majority of which are excreted in feces, and a number of which are well equipped to be pathogenic.
The species that are present in the vagina vary between premenopausal woman and those who have gone through menopause.
The microbiota of healthy premenopausal woman is generally dominated by Lactobacillus species, the most common of which are L. iners, L. crispatus, L. gasseri, L. jenesenii, followed by L. acidophilus, L. fermentum, L. plantarum, L. brevis, L. casei, L. vaginalis, L. delbrueckii, L. salivarius, L. reuteri, and L. rhamnosus
Lactobacilli are the organisms of most importance to vaginal health, and
hormonal changes, vaginal pH, and glycogen content can all affect the ability of lactobacilli to adhere to epithelial cells and colonize the vagina.
The menstrual cycle can also cause changes in the vaginal microbiota.
High concentrations of estrogen increase the adherence of lactobacilli to vaginal epithelial cells.
With the decrease in estrogen levels associated with menopause, there is also a decrease in lactobacilli present in the vaginal tract of postmenopausal women.
Postmenopausal women are also more susceptible to urogenital infections, suggesting supporting colonization of the vagina by lactobacilli protects from these pathogens.
Lactobacilli adhere to and to populate the vaginal epithelium and mucin layer, inhibit pathogens from taking over, and reduce pathogen virulence, and modulate host defenses.
Hormone replacement therapy (HRT) alters the bacterial profile and restores a lactobacilli-dominated state, and reduces the incidence of urinary tract infections
The vaginal tract dominated by lactobacilli protects the host against some vaginal infections, it does not fully prevent colonization by other species.
Pathogens are still able to coexist with these commensal organisms.
The balance between a healthy and diseased state involves factors, such as hormone levels, douching, sexual practices, as well bacterial interactions and host defenses.
Pathogenic organisms are able to infect the vagina, with BV, yeast vaginitis, and UTIs organisms can be transmitted as nonsexually transmitted.
Yeast vaginitis is characterized by white discharge, local itching, and irritation, and the majority of cases are caused by Candida albicans, but C. glabrata, C. krusei, and C. tropicalis can be problematic?
It is diagnosed by microscopic detection of dense numbers of yeast cells on a vaginal smear, and by physical examination and the presence of a white, mucous-like yeast discharge.
Lactobacilli are often found in patients with yeast vaginitis, therefore, the induction of infection does not appear to require the yeast displacing or killing off the lactobacilli.
UTIs occur when pathogenic bacteria ascend from the vagina and replicate on the bladder urothelium.
UTIs are frequent among women, with an estimated 50% suffering at some time in their life.
In women with no history of UTI, their vagina and perineum is most commonly colonized by lactobacilli.
In women with recurrent UTI there is an inverse association between lactobacilli and E. coli, suggesting that lactobacilli play a role in preventing infection.
The most common urogenital disorder in women of reproductive age is BV.
The vaginal microbiota of BV patients typically contains a broader range of species than found under healthy conditions, with Atopobium vaginae, Bacteroides spp., Gardnerella vaginalis, Mobiluncus, Megasphera, Mycoplasma hominis, Peptostreptococcus, and Prevotella being particularly prevalent.
Bacterial vaginosis is associated with multiple species of bacteria that occur in 90% of the cases, and essentially consists of an elevated vaginal pH (>4.5) and depletion of lactobacilli.
Bacterial vaginosis affects women of all age groups, and is often asymptomatic.
When symptoms and signs do occur, they include fishy odor, discharge, and vaginal pH above 4.5.
Criteria for BV diagnosis: presence of at least 3 of the following criteria: (1) release of an amine or fishy odor upon addition of 10% potassium hydroxide, (2) a vaginal pH higher than 4.5, (3) detection of at least 20% of clue cells, which are vaginal cells colonized by Gram-negative rods, and (4) a milky homogeneous vaginal discharge.
A Gram-staining method called the Nugent score comprises a scoring system based on the morphology of bacteria present in vaginal swab samples.
A normal Nugent score is given to samples showing predominantly Gram-positive rods indicative of lactobacilli
The presence of predominantly small and curved shaped Gram-negative rods and Gram-positive cocci, along with the absence of lactobacilli, is indicative of BV on the Nugent Gram stain.
The BVBlue test is works by detecting sialidase produced by pathogens associated with the bacterial vaginosis.
Aerobic vaginitis can occur when the vagina is colonized by organisms such as E. coli and enterococci.
BV during can increase the risk of preterm labor and low birth weight.
BV may be associated with pelvic inflammatory disease, UTI, and increased susceptibility to sexually transmitted diseases, including HIV.
The organisms associated with
Bacterial vaginosis organisms can form biofilms on the vaginal epithelium, and are associated with increased resistance to lactobacilli-produced lactic acid and hydrogen peroxide which are normally antagonistic to such organisms.
The vaginal epithelium biofilms are also able to induce host expression of inflammatory factors, such as IL-1 and IL-8.
It is suspected increased prevalence of H2O2-peroxide producing vaginal lactobacilli in healthy women is a protective factor for BV.
Young girls who suffer from UTI are more likely to have repeated episodes in adulthood.
Many UTI, BV, and yeast vaginitis patients have recurrences.
Recurrent infections may also be due to the elimination of the commensal organisms in the vagina by the antimicrobials, increasing susceptibility to recolonization by pathogens.
Use of probiotics intravaginally to replenish the commensal microbes lowers the risk of reinfection.
The concept of delivering lactobacilli orally to repopulate the vagina is supported the concept that ingested strains could pass through the intestine, reach the rectum, and
ascend to the vagina.
An oral dose of over one billion organisms per day maintains a lactobacilli-dominated vaginal presence.
Time for oral lactobacilli to affect the vaginal tract is obviously longer than direct vaginal instillation, and will depend on viability of the strains as they pass through the stomach and gut.
An advantage of the oral approach may be the ability of the lactobacilli to reduce the transfer of yeast and pathogenic bacteria from the rectum to the vagina, which could potentially lower the risk of infection.
The mechanisms whereby lactobacilli function as anti-infective defenses are not fully understood.
Probiotics can augment the effects of antibiotics in treatment of vaginal disease.
Probiotics are administered worldwide, and those administered for urogenital health have been well tolerated.
The mouth, gastrointestinal tract, and female genitourinary tract are inhabited by Lactobacillus.
The use of probiotic lactobacilli to prevent infection has rationale, safety record, but so far only a few strains have been clinically proven to be effective, in particular to prevent bacterial vaginitis.