Gardnerella vaginalis (Bacterial vaginosis)

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Gardnerella vaginalis (Bacterial vaginosis)



Gardnerella vaginalis (Bacterial vaginosis)


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Gardnerella vaginalis (Bacterial vaginosis)

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USMLE® Step 1 style questions USMLE

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A 23-year-old female comes to the office for evaluation of abnormal vaginal discharge. The patient has been experiencing increasing amounts of malodorous vaginal discharge for the past 4-5 days. Her last menstrual period was 3 weeks ago, and she did not have any postcoital or intermenstrual bleeding. Past medical history is significant for chlamydial cervicitis at the age of 17. The patient has been sexually active with a new male partner for the past 3 weeks, and they consistently use barrier contraception. Vitals are within normal limits. Physical examination reveals off-white, watery discharge throughout the vaginal vault. There is no vulvar or vaginal erythema. A sample of the discharge is collected and mixed with potassium hydroxide, which produces a fish-like smell. A saline wet mount examination is performed. Which of the following would most likely be visualized under microscopy? 

External References

First Aid








Bacterial vaginosis

Gardnerella vaginalis p. , 146

Gardnerella spp. p. 122

Gardnerella vaginalis p. , 146

labs/findings p. 720

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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.


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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