Disease

 Gardnerella vaginalis is the main organism associated with bacterial vaginosis. This disease is the most common vaginal infection of sexually active women.

 Important Properties

Gardnerella vaginalis is a small, facultative gram-variable rod. The term “gram-variable” refers to the observation that some organisms are purple while others are pink in a Gram-stained specimen. Structurally, it has a gram-positive cell wall but the wall is thin and older organisms tend to lose the purple color.

Pathogenesis

 The pathogenesis of bacterial vaginosis is uncertain. Gardnerella vaginalis is often found in association with anaerobes such as Mobiluncus  and together they cause the symptoms of this disease. It is not considered to be a sexually transmitted infection.

Clinical Findings

 Bacterial vaginosis is characterized by a malodorous, white or gray-colored vaginal discharge. The discharge has a characteristic “fishy” odor. Inflammatory changes are typically absent which is why it is called a “vaginosis” rather than a “vaginitis.” Mild itching may occur. Women with bacterial vaginosis have a higher incidence of pre term deliveries and, consequently, a higher incidence of morbidity and mortality occurs in their newborn children.

Laboratory Diagnosis

Glue cells, which are vaginal epithelial cells covered with bacteria, are an important laboratory finding seen in a microscopic examination of the vaginal discharge (Figure 1). In addition, the “whiff” test, which consists of treating the vaginal discharge with 10% KOH and smelling a pungent, “fishy” odor, is often positive. However, trichomoniasis, which can also cause a positive whiff test, must be ruled out before a diagnosis of bacterial vaginosis can be made. A pH of greater than 4.5 of the vaginal discharge supports the diagnosis of bacterial vaginosis.

FIG1.  Clue cells in bacterial vaginosis. Note that the lower epithelial cell is a "clue cell" because its surface is covered with bacteria. The upper epithelial cell is not a "clue cell" because its surface has few bacteria. (Reproduced with permission from Usatine RP et al: The Color Atlas of Family Medicine, New York: McGraw-Hill, 2009. Courtesy of E.J. Mayeaux, Jr., MD.)

Treatment and Prevention

The drug of choice is metronidazole. Treatment of sexual partners is not recommended. There is no vaccine.