Gardnerella vaginalis (Bacterial vaginosis)

Definitions & Key takeaways

Gardnerella vaginalis is a gram-variable coccobacillus, non-motile and facultative anaerobic bacterium, known to cause bacterial vaginosis (BV). This is a condition where the natural balance of bacteria in the vagina is disrupted and replaced by an overgrowth of certain bacteria. The symptoms of BV include discharge from the vagina that may be white, gray, or green; a strong fishy odor; and vaginal itching. BV is a common condition and is usually treated with antibiotics.

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Gardnerella vaginalis, or G. Vaginalis for short, is a gram-variable coccobacillus present in low numbers in normal vaginal flora.
Normally, the vaginal flora is made up mostly of Lactobacilli, which keep vaginal pH below 4.5. When the number of Lactobacilli decreases, that results in an imbalance of vaginal flora which increases the vaginal pH.
This allows G. vaginalis to proliferate, causing Bacterial Vaginosis, or BV which is the most common vaginal infection in females of reproductive age.Now, G.
vaginalis is gram-variable, which means it can stain either positive or negative with Gram-staining. Ok, so normally, whether a bacteria is Gram-positive or Gram-negative is determined by the amount of peptidoglycan in their cell wall.
Bacteria with a thick peptidoglycan wall take in the purple dye used during Gram staining, so they’re Gram-positive. Bacteria with a thin peptidoglycan wall can’t retain the purple dye, and instead stain pink with the Safranin dye used during Gram-staining.
So, Gram-variable bacteria, like G. vaginalis, first appear Gram-positive and then, as the culture ages, they gradually lose the peptidoglycan in their wall, and once their wall is too thin to retain purple color, they become Gram-negative.
Finally, G. vaginalis is non-spore forming, non-motile and facultative anaerobic which means it can survive in both aerobic and anaerobic environments.Now, when vaginal pH increases, G.
vaginalis can use a number of virulence factors to cause disease. What is more, along with G.
vaginalis, a number of other anaerobic bacteria species can proliferate, like Mobiluncus, Bacteroides or Prevotella which are also present in low numbers in normal vaginal flora - resulting in a mixed infection.Ok, now, G.
vaginalis produces a cytotoxin called vaginolysin and an enzyme called sialidase, and both of these help it adhere to the vaginal epithelial cells and colonize the vaginal epithelium.
Also, sialidases can cleave the sialic acid residues that keep the vaginal epithelial cells in place, so this makes easier for cells to detach from one another, causing desquamation of the epithelium.Then, G.
vaginalis produces proteolytic carboxylase enzymes which will break down vaginal peptides into volatile amines, which have an unpleasant smell.
Once they colonize the epithelium, the bacteria multiply and form a bacterial biofilm. A biofilm is basically a layer of goop-like material made of exopolysaccharides or eps, within which bacteria live and reproduce.
Comparing a biofilm to strawberry jam, the seeds would be the bacteria and the rest of the jam would be the EPS. In this biofilm, the bacteria can hide from the host’s immune system and antibiotics.
Left untreated, the bacterial infection can spread to the cervix, causing cervicitis, and from there, make its way to the uterus, causing endometritis.Now, risk factors for developing Bacterial Vaginosis are factors that alter the normal vaginal flora.
More specifically, these factors decrease the number of Lactobacilli which normally predominate in the vagina. One such risk factor is having a new sexual partner, or multiple sexual partners - however, Bacterial Vaginosis is not a sexually transmitted infection, as it doesn’t colonize the male reproductive tract, so it is solely a bacterial imbalance of the female reproductive system.
Other risk factors may include douching, antibiotics and use of intrauterine devices.Now, bacterial vaginosis typically presents with a thin white or gray vaginal discharge, made up of desquamated epithelial cells.
The discharge typically has an unpleasant fishy smell, on account of volatile amines. And this is typically the only symptom.
If there are other symptoms, like vaginal pain, itching, burning, dysuria, which means pain during urination, and dyspareunia, which is pain during sexual intercourse, that suggests a mixed infection, particularly with mobiluncus.
Also, HIV-infected women with bv have a higher risk to transmit HIV than those without BV, and the presence of BV during pregnancy may increase complications such as premature birth and miscarriage.Diagnosis of Bacterial Vaginosis is most commonly done with Amsel criteria, and three out of the following four must be met for the diagnosis.
First, there must be a thin white or gray vaginal discharge. Second, vaginal pH must be above 4.5.
Third, there’s a positive Whiff-Amine test. To test for that, a sample of vaginal discharge is smeared on a slide, and a drop of 10% Potassium hydroxide or KOH is added to it - and with Bacterial Vaginosis, there will be a fishy odor.
Finally, on microscopy of a discharge sample, there are clue cells, which are vaginal epithelial cells that have coccobacilli on their edges, so it looks like the borders of the cells are stippled.Another way to diagnose BV is by evaluating a gram stain of the vaginal fluid using Nugent criteria or Hay/Ison criteria, and count the number of Lactobacilli and BV-associated bacteria found in a probe.
However, this takes more time and resources than the Amsel criteria, so it’s mostly used in a research setting. If microscopy is not available, tests like the Affirm VP III test and the OSOM BVBlue test can be done.
The Affirm VP III test is an automated test for detecting high concentrations of G. vaginalis on a vaginal discharge sample.
The OSOM BVBlue test, on the other hand, uses a chromogenic substrate of bacterial sialidase to identify its activity in a vaginal sample.
Chromogenic literally means “color generating” - so if the sample has high levels of sialidase it will appear blue or green and it if has no sialidase or low levels it will appear yellow.Finally, bacterial vaginosis is treated with Metronidazole for a period of 7 days.##SummaryAlright, as a quick recap, gardnerella vaginalis is a gram-variable coccobacillus, non-spore forming, non-motile and facultative anaerobic.
It has virulence factors like vaginolysin and sialidases, which help it colonize the vaginal epithelium, and it also creates biofilms, which can help it proliferate hidden from antibiotics or the immune system.
It causes a disease called bacterial vaginosis which typically presents with a thin white or gray vaginal discharge with a