**Core Concept**
Bacterial vaginosis (BV) is a common vaginal infection caused by an imbalance of the normal vaginal microbiota, characterized by a decrease in lactobacilli and an overgrowth of various anaerobic bacteria. The diagnosis of BV is primarily made based on the presence of specific microscopic findings, including a "clue cell" and a shift in the vaginal flora.

**Why the Correct Answer is Right**
The presence of clue cells is a hallmark of bacterial vaginosis. Clue cells are vaginal epithelial cells that are coated with bacteria, making them appear stippled or granular under microscopic examination. The presence of clue cells is diagnostic of BV and is often used in conjunction with the Nugent score, which takes into account the number of lactobacilli and the presence of various bacteria. The Nugent score is used to quantify the degree of vaginal colonization by different bacteria.

**Why Each Wrong Option is Incorrect**
**Option A:** This option may be tempting, but it is actually a characteristic finding in bacterial vaginosis. The presence of various bacteria, including Gardnerella vaginalis, is a key feature of BV.
**Option B:** This option is incorrect because the presence of a mixed bacterial flora, including anaerobes and facultative anaerobes, is a hallmark of bacterial vaginosis.
**Option C:** This option is incorrect because the presence of an inflammatory response, including an increase in white blood cells, is not typically seen in bacterial vaginosis.

**Clinical Pearl / High-Yield Fact**
Bacterial vaginosis is a common cause of vaginal discharge in women of reproductive age and is often associated with an increased risk of preterm labor and other complications. The diagnosis of BV is primarily made based on microscopic findings, including the presence of clue cells, and is often treated with metronidazole or other antibiotics.

**Correct Answer: D.**