**Core Concept**
The **vaginal flora** is composed of various microorganisms, with **lactobacilli** being the predominant species in a healthy individual. These microorganisms play a crucial role in maintaining the **vaginal ecosystem**. The balance of the vaginal flora is essential for preventing infections.

**Why the Correct Answer is Right**
The correct answer is related to the type of bacteria that is commonly found in the vagina. **Lactobacillus** species are the most prevalent and are important for maintaining the acidic pH of the vagina, which helps to prevent the growth of pathogenic microorganisms.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not represent the normal vaginal anaerobe.
**Option B:** This option is also incorrect as it is not the typical anaerobe found in the vagina.
**Option C:** This option is incorrect because, although it may be present, it is not the primary anaerobe.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that an imbalance of the vaginal flora, also known as **dysbiosis**, can lead to various infections, including **bacterial vaginosis**.

**Correct Answer: D. Lactobacillus**