**Core Concept**
Bacterial vaginosis (BV) is a common vaginal infection caused by an imbalance of the normal vaginal microbiota, characterized by a decrease in the levels of lactobacilli and an overgrowth of anaerobic bacteria, particularly Gardnerella vaginalis.

**Why the Correct Answer is Right**
Bacterial vaginosis is defined by the presence of clue cells, which are vaginal epithelial cells that have adherent bacteria, and a decrease in the pH of the vaginal discharge, typically less than 4.5. The diagnosis of BV is primarily clinical and is based on the presence of three or four of the Amsel criteria: a thin, white or gray vaginal discharge; a pH of less than 4.5; the presence of clue cells; and a fishy odor.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a characteristic feature of bacterial vaginosis. Clue cells are vaginal epithelial cells that have adherent bacteria, and their presence is a key diagnostic criterion for BV.
**Option B:** This option is incorrect because a decrease in pH is a hallmark of bacterial vaginosis. The pH of the vaginal discharge is typically less than 4.5 in women with BV.
**Option C:** This option is incorrect because Gardnerella vaginalis is one of the primary bacteria responsible for causing bacterial vaginosis.

**Clinical Pearl / High-Yield Fact**
Bacterial vaginosis is a common cause of vaginal discharge in women of reproductive age and is associated with an increased risk of pelvic inflammatory disease, preterm labor, and postpartum endometritis.

**Correct Answer: D.**