Bacterial Vaginosis and Gardnerella
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Direct answer
Bacterial vaginosis is a polymicrobial imbalance in which protective Lactobacillus species are replaced by an overgrowth of anaerobes, with Gardnerella vaginalis as the most recognised organism involved. It is diagnosed clinically by the Amsel criteria, where three of four features are needed, or by the Nugent score on a Gram-stained vaginal smear. Metronidazole is the standard treatment, and most cases are not sexually transmitted infections in the usual sense.
What you must remember
- Gardnerella vaginalis: a small, Gram-variable coccobacillus that can also be found in some healthy women.
- Pathogenesis: loss of Lactobacillus species raises the vaginal pH, allowing overgrowth of Gardnerella, Mobiluncus and other anaerobes.
- Amsel criteria: thin homogeneous grey discharge, vaginal pH above 4.5, a positive whiff test and clue cells, with three of four needed for diagnosis.
- Clue cells: vaginal epithelial cells covered by coccobacilli, with more than 20 per cent of epithelial cells affected.
- Nugent score: a 0 to 10 score on a Gram-stained smear, where 7 to 10 indicates bacterial vaginosis, 4 to 6 is intermediate and 0 to 3 is normal.
- Symptoms: thin grey discharge with a fishy odour, especially after intercourse, with little itching or inflammation.
- Treatment: oral metronidazole for seven days or metronidazole gel, with clindamycin as an alternative.
- Pregnancy: bacterial vaginosis is linked to preterm birth, so symptomatic pregnant women are treated.
Where the exam tries to catch you
Bacterial vaginosis questions turn on the organism, the discharge pattern and the correct drug.
- Trap: treating Gardnerella as the single cause of bacterial vaginosis Correct: the condition is a polymicrobial imbalance, and Gardnerella is one of several organisms involved.
- Trap: labelling itching with a thick white discharge as bacterial vaginosis Correct: that picture suggests candidiasis, whereas bacterial vaginosis has a thin grey discharge and a positive whiff test.
- Trap: choosing fluconazole for bacterial vaginosis Correct: metronidazole or clindamycin is used, and fluconazole is the drug for candidiasis.
Frequently asked questions
Why is Gardnerella vaginalis not the sole cause of bacterial vaginosis?
Gardnerella vaginalis is one of several anaerobic and facultative organisms that overgrow when protective Lactobacillus species are lost in bacterial vaginosis. The condition is therefore a polymicrobial imbalance, and Gardnerella vaginalis alone does not explain it.
What are the Amsel criteria for bacterial vaginosis?
The Amsel criteria are four clinical features: thin homogeneous grey discharge, vaginal pH above 4.5, a positive whiff test and clue cells on microscopy. Bacterial vaginosis is diagnosed when three of these four criteria are present.
What is the Nugent score in bacterial vaginosis?
The Nugent score is a 0 to 10 score from a Gram-stained vaginal smear, based on counts of Lactobacillus, Gardnerella and Mobiluncus morphotypes. A score of 7 to 10 indicates bacterial vaginosis, 4 to 6 is intermediate and 0 to 3 is normal.
Which drug treats bacterial vaginosis?
Oral metronidazole for seven days, or metronidazole gel, is the first-line treatment for bacterial vaginosis per current guidance. Clindamycin is an alternative, and routine treatment of the male partner after a first episode is not needed, although newer guidance allows considering partner treatment in recurrent disease.
Why is bacterial vaginosis important in pregnancy?
Bacterial vaginosis in pregnancy is associated with preterm birth and early pregnancy loss, so symptomatic pregnant women are usually treated. Metronidazole is the usual drug, and decisions in pregnancy follow current obstetric guidance.