Metachromatic granules are stained by-
**Core Concept**
Metachromatic granules are structures found in certain bacteria, such as *Corynebacterium diphtheriae*, and are involved in the storage of phosphate. The staining of these granules is an important diagnostic tool. The **metachromatic** property refers to the ability of these granules to stain a different color than the surrounding tissue or cell.
**Why the Correct Answer is Right**
The correct answer is related to the specific dye used to stain metachromatic granules. **Toluidine blue** and **methylene blue** are commonly used dyes, but the most specific answer is not provided. However, in general, metachromatic granules are stained by basic dyes, which bind to the acidic components of the granules.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the specific dye is not identified.
**Option B:** This option is incorrect because the specific dye is not identified.
**Option C:** This option is incorrect because the specific dye is not identified.
**Option D:** This option is incorrect because the specific dye is not identified.
**Clinical Pearl / High-Yield Fact**
Metachromatic granules are a key diagnostic feature of *Corynebacterium diphtheriae*, and their staining is an important tool in microbiology. The ability to identify these granules can aid in the diagnosis of diphtheria.
**Correct Answer:** D. Toluidine blue.