The vaginal microbiome is home to millions of different microorganisms and is usually dominated by Lactobacillus — the "good" bacteria responsible for keeping your vaginal pH low and keeping infections at bat. Sometimes, though, there can be a shift in the microbial composition within the vagina, which can result in dysbiosis (the medical term for an imbalanced microbiome). This can happen when anaerobic bacteria, including Prevotella, which can survive in oxygen-free environments, become more prevalent. When this happens, it can lead to conditions such as bacterial vaginosis (BV).

Unfortunately, Prevotella species are notoriously difficult to study, as they're fastidious bacteria and require very specific growing conditions. As a result, we didn't know much about them before the advent of genomic sequencing technology. However, now that we can detect them by sequencing, we are starting to learn a lot more about them.

Below is a summary of what scientists know about Prevotella and how it is linked to bacterial vaginosis. Keep scrolling to learn more!

What is Prevotella bivia?

Prevotella spp. (an umbrella term that encompasses the bacterial species of the Prevotella genus) are anaerobic bacteria that inhabit many parts of the human body. Although common in the gut microbiome, they may be a sign of infection if found in the vagina. 

They’re considered commensal (harmless) microbes typically found in the intestinal tract of people who consume a fiber-rich diet. As many as 50 species have been found in various parts of the body, including the skin, oral cavity, and most importantly, the vagina. However, some species of Prevotella (such as P. bivia, P. timonensis, and P. amnii). can cause infections and microbial imbalances if present in other parts of the body.

Among the different species of vaginal Prevotella, P. bivia is the most well-known and extensively studied. This species is often associated with bacterial vaginosis and adverse pregnancy outcomes such as preterm birth. P. bivia and Gardnerella have what is known as a symbiotic relationship, and when they come together, they consume available nutrients, producing chemical byproducts that can increase vaginal pH. 

Additionally, these microbes also create compounds that can help them ward off immune cells. As a result, during bacterial vaginosis, G. vaginalis and P. bivia increase in abundance without causing a strong enough inflammatory response, which sets the stage for infection. 

Does Prevotella cause bacterial vaginosis? 

The exact cause of bacterial vaginosis is unknown. One BV-associated bacteria is Gardnerella, which is present in up to 95% of bacterial vaginosis cases. However, it's also found in many women who don't have BV. While Gardnerella may play a role in causing BV, it alone is not enough to cause the condition. Prevotella could also be involved.  

Bacterial vaginosis occurs due to an imbalance in the vaginal microbiome. When the normal vaginal microbiota get disrupted, Gardnerella and Prevotella are believed to be the first to colonize the vaginal environment. 

In the absence of protective bacteria like Lactobacillus, Gardnerella and Prevotella thrive and produce an enzyme called sialidase. Sialidases break down sialic acid, a component of mucins that form the vaginal mucosa protecting epithelial cells. Recent research has found that almost all species of Prevotella produce sialidase, which they use to break down mucin and gain access to the vaginal epithelium (the lining of the vagina).

These bacteria create a sort of "home" for themselves by forming a biofilm when they degrade the vaginal mucosa. This biofilm is like a scaffold that other bacterial species, including Prevotella, can use to enter and thrive. 

Gardnerella and Prevotella have a symbiotic relationship, which essentially means they get along really well and help each other grow — like besties. Gardnerella consumes nutrients from the vaginal environment and produces byproducts called metabolites. Some of these metabolites are actually super important food sources for Prevotella, which it might not be able to get otherwise. 

As Prevotella eats this food, it produces its own byproduct called ammonia, which Gardnerella can use. This is a really cool relationship that allows both bacteria to thrive together in the same biofilm, and over time, more BV-associated bacteria (BVAB) enter into this cozy environment, forming the polymicrobial biofilm that is often seen in bacterial vaginosis.

On top of that, Prevotella produces more than just ammonia that feeds Gardnerella. When Prevotella consumes available carbon, it produces byproducts such as acetate and succinate, which can affect vaginal pH, a telltale sign of bacterial vaginosis. These byproducts inhibit the movement of your immune cells, making it harder for them to fight off bacterial invaders. But don't worry, Prevotella is just trying to protect the biofilm it has established in your body. 

It's important to remember that bacterial vaginosis is not caused solely by Gardnerella or Prevotella, and the early colonization and biofilm formation may not show any symptoms. Symptoms may only appear when other types of bacteria have entered and established themselves within the biofilm.

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Prevotella and vaginal odor 

Bacterial vaginosis is characterized by vaginal discharge with a strong fishy odor. Well, did you know that Prevotella is one of a handful of organisms responsible for that odor?

Certain vaginal bacteria release chemicals called biogenic amines that are smelly, specifically chemicals called putrescine and cadaverine. These biogenic amines smell like rotting meat or rotting fish.

Right now, Dialister, Prevotella, Parvimonas, Megasphaera, Peptostreptococcus, and Veillonella are suspected to be responsible for producing most of the smelly molecules, because they have the genes required to produce biogenic amines. 

Why can’t my body clear bacterial vaginosis on its own?

Remember those pesky sialidases Gardnerella uses to infiltrate the mucosa? P. bivia also possesses sinister sialidases, aiding Gardnerella in degrading mucins, but those aren’t the only thing sialidases degrade. 

Sialidases can also affect the stability of secretory-IgA (sIgA). These special antibodies are produced by your body to fight off harmful bacteria or viruses by marking them for your immune cells to clear them from your system. Unfortunately, by destabilizing sIgA, certain bacteria can evade your natural immunity. 

Interestingly, a recent study has suggested that people who experience bacterial vaginosis can be divided into two groups: those who mount an effective immune response and those who don't. Those who mount an immune response against common BV-associated bacteria have a better chance of successful treatment and reduced relapse. 

In contrast, those who don't mount an immune response are more likely to encounter treatment failure and relapse. Please note that this is not your fault and is more likely due to the sialidases, succinate, and acetate made by BVAB, such as Prevotella.

Prevotella treatment 

The first line of treatment for bacterial vaginosis typically involves antibiotics like clindamycin or metronidazole. There are also a couple of other options like tinidazole and secnidazole. While many people see improvement with these treatments, more than half of women with BV experience a recurrence of the infection within six months. 

It's important to know that oral metronidazole treatment doesn't destroy the polymicrobial biofilm created by the cooperation between Gardnerella and Prevotella. Biofilms are like safe homes for bacteria that protect them from external threats, just like our homes protect us from extreme weather. As a result, biofilms can shield bacteria from antibiotics, making it harder to get rid of the infection. While metronidazole suppresses biofilm growth, it doesn't eliminate it completely. So, even after finishing the antibiotic course, bacteria remain in the biofilm, ready to start growing again, which is why BV recurrence is so common. 

Should I be concerned if I have Prevotella spp.

Remember, Prevotella simply being present in your vaginal tract doesn’t cause BV. Prevotella are common commensals, and most of us have Prevotella living in our bodies. Fun fact: Prevotella are actually beneficial in the gut microbiome! It’s dysbiosis, where your normal vaginal microbiota has been disrupted, that allows these bacteria to bloom and set the stage for BV.  

However, a recent study suggests there may be future benefits to knowing what kind of G. vaginalis and P. bivia reside within you. Researchers analyzed the metabolic profiles of several G. vaginalis isolates grown with P. bivia. They found that some G. vaginalis isolates were better able to interact with and support the growth of P. bivia and vice versa. This suggests that the potency of G. vaginalis and P. bivia cooperation may depend on the functions of the specific strains in question. 

This is a very new area of study, so we still don’t know which combinations of strains are more likely to result in BV symptoms. It’s nearly impossible to replicate the vaginal microenvironment in a lab setting but research advances represent hope for the future that we may begin to untangle the complexities of polymicrobial interactions that are the cause of BV. 


​​How do you get Prevotella?

Most of us have Prevotella already in our bodies. It’s a harmless bacteria in of itself and can actually be beneficial to gut health. However, in a state of dysbiosis, species like P. bivia, P. timonensis, and P. amnii can overgrow and cause BV. 

Is Prevotella good or bad?

Whether a type of bacteria is good or bad depends on the environment it’s in. Prevotella are known as commensals, which are types of microbes that live either on the surface of the body or in the mucosa without harming human health. The bacterial species in some circumstances, and problematic in others. Prevotella can be beneficial to the gut, but growth of Prevotella in the vagina leads to BV if it’s present in high amounts. 

What disease is caused by Prevotella?

P. bivia is most commonly linked to BV, but it’s worth noting that the presence of Prevotella alone isn’t enough to cause BV. 

What antibiotic treats Prevotella?

Antibiotics commonly used to treat Prevotella include clindamycin and metronidazole, as well as alternatives such as tinidazole or secnidazole.