**Core Concept**
Bullous impetigo is a skin infection characterized by the formation of large blisters or bullae. It is a type of impetigo, a superficial bacterial infection of the skin, and is most commonly caused by a specific type of bacteria.

**Why the Correct Answer is Right**
Bullous impetigo is primarily caused by Staphylococcus aureus, a gram-positive bacterium that produces exfoliative toxins. These toxins cause the skin cells to separate, leading to the formation of large blisters or bullae. Staphylococcus aureus is highly contagious and can easily spread through contact with an infected person or contaminated objects. The bacteria produce a toxin that cleaves the desmoglein 1 protein, a key component of the epidermal cell-to-cell adhesion, resulting in the formation of bullae.

**Why Each Wrong Option is Incorrect**
**Option A:** Streptococcus, while a common cause of skin infections, is not typically associated with bullous impetigo. Streptococcal infections can cause a different type of impetigo, known as non-bullous impetigo.
**Option C:** This is a duplicate of the correct answer, Staphylococcus, and is therefore incorrect.
**Option D:** Yersinia pestis is the causative agent of plague, a zoonotic disease that affects humans through the bites of infected fleas or direct contact with infected animals. It is not associated with bullous impetigo.

**Clinical Pearl / High-Yield Fact**
Bullous impetigo can be treated with topical or oral antibiotics, and prompt treatment is essential to prevent the spread of the infection and reduce the risk of complications. It's essential to note that bullous impetigo requires a specific type of treatment, and the choice of antibiotic should be guided by the susceptibility patterns of the causative organism.

**✓ Correct Answer: B. Staphylococcus**