A 35-year-old woman complains of vaginal discomfort for 2 weeks. Physical examination reveals a scanty vaginal discharge. The fluid develops a "fishy" odor after treatment with 10% potassium hydroxide. A Pap smear taken during the pelvic examination shows squamous cells covered by coccobacilli ("clue" cells). Which of the following is the most likely etiology of vaginal discomfort in this patient?

Sexual transmission of G. vaginalis, a Gram-negative coccobacillus, causes a substantial proportion of cases classified as nonspecific vaginitis. The diagnosis of Gardnerella infection is best established by identifying the organisms either in a wet mount specimen of a vaginal discharge or in a Papanicolaou-stained smear. The "clue cell" is pathognomonic and shows squamous cells covered by coccobacilli. Other aids to the diagnosis are a thin, homogeneous, milk-like vaginal discharge, a vaginal pH above 4.5, and the presence of a "fishy" odor from the discharge once alkalinized with 10% potassium hydroxide. Viruses (choices C and D) do not produce vaginal discharge. Choices A and E are not associated with "clue" cells.Diagnosis: Vaginitis, cervicitis