**Core Concept**
The differentiation between staphylococci and micrococci relies on the ability to distinguish between these closely related genera based on their biochemical characteristics. Staphylococci and micrococci are both gram-positive, catalase-positive cocci, but they can be differentiated by their oxidase activity.

**Why the Correct Answer is Right**
The modified oxidase test is a key tool in differentiating staphylococci and micrococci. This test detects the presence of cytochrome c oxidase, an enzyme found in micrococci but not in staphylococci. The test involves adding 1% tetramethyl-p-phenylenediamine (TMPD) and 0.01% phenazine ethosulfate to the bacterial suspension. A positive reaction, indicated by a color change, is characteristic of micrococci. This is because the oxidase enzyme in micrococci catalyzes the oxidation of the tetramethyl-p-phenylenediamine, resulting in a purple color.

**Why Each Wrong Option is Incorrect**
**Option A:** The catalase test is used to differentiate catalase-positive bacteria (like staphylococci and micrococci) from catalase-negative bacteria (like streptococci). However, it is not specific for differentiating between staphylococci and micrococci, as both genera are catalase-positive.

**Option C:** Gram staining is a method used to differentiate bacteria based on their cell wall composition and is not useful for differentiating between staphylococci and micrococci.

**Option D:** The Auramine Fluorochrome Stain (AFS) is used for staining mycobacteria and is not relevant to the differentiation between staphylococci and micrococci.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the modified oxidase test is a critical tool in identifying micrococci, which can be mistaken for staphylococci based on their gram-positive, catalase-positive characteristics. The test's specificity for micrococci makes it a valuable diagnostic tool in microbiology.

**✓ Correct Answer: B. Modified Oxidase test**