Staphylococcus is –
**Core Concept**
Staphylococci are a type of Gram-positive, spherical bacteria belonging to the family Staphylococcaceae. They are commonly found on the skin and mucous membranes of humans and other animals. Staphylococci are known to cause a variety of infections, ranging from mild to life-threatening.
**Why the Correct Answer is Right**
Staphylococci are distinguished from other bacteria by their unique morphology and growth characteristics. They are typically arranged in clusters or grape-like colonies on agar plates, which is a key identifying feature. In addition, staphylococci are capable of producing a range of virulence factors, including toxins and enzymes that contribute to their pathogenicity.
**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because Staphylococcus is not a genus of Gram-negative bacteria. While some staphylococci may have Gram-negative characteristics, they are fundamentally Gram-positive.
**Option B:**
This option is incorrect because Bacillus is a different genus of bacteria altogether, characterized by their rod-shaped morphology and ability to form endospores.
**Option C:**
This option is incorrect because Corynebacterium is a genus of bacteria that is typically associated with respiratory tract infections and is not known for forming clusters or grape-like colonies.
**Clinical Pearl / High-Yield Fact**
One important point to remember is that Staphylococcus aureus is a particularly virulent species that can cause a range of serious infections, including pneumonia, sepsis, and skin and soft tissue infections.
**Correct Answer:** A. Staphylococcus.