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Long rods staining purple in a Gram-stained vaginal smear indicate Lactobacillus as a dominant feature of the microbiome

Clinical Background

Bacterial vaginosis (BV) is the most common of all vaginal conditions that bring women to healthcare providers. It is characterized by a loss of beneficial normal flora (lactobacilli) and an overgrowth of other bacteria. Women with BV are at greater risk of intrauterine and placental infections, preterm labor with delivery of premature low birth weight infants, endometritis, and pelvic inflammatory disease. They are also at greater risk of acquiring sexually transmitted infections and urinary tract infections.

The clinical criteria for BV (Amsel critera), include 'thin' vaginal fluid, fishy odor upon potassium hydroxide treatment, elevated vaginal pH (>4.5) attributed to reduced lactic acid bacteria, and microscopic examination demonstrating exfoliated epithelial cells that are studded with attached bacteria (“clue cells” see Figure). Conventional treatments are often followed by recurrences of BV and little progress has been made improving pregnancy outcomes associated with BV. 

sialidase activity
sialic acid

Gardnerella vaginalis

Gardnerella is often found in large numbers in women with BV. Many but not all Gardnerella strains produce sialidase, believed to be one of the primary sialidase producing organisms in the BV microbiome. 

Gardnerella inoculation of the mouse vagina is sufficient to result in sialidase activity in vaginal fluids (see PLoS, 2013).

Sialidase activity in BV

BV is frequently characterized by the presence of sialidase activity in vaginal fluids. In fact, sialidase activity is now used as a diagnostic feature of BV. 

In general, sialidases remove the outermost sialic acid residues from sugar chains. However, the potential roles of sialidases in BV are not fully understood.

X-ray tomography of the vagina and uterine horns of a nonpregnant mouse
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