**Core Concept**
Streptococcus is a genus of gram-positive, facultatively anaerobic bacteria that can cause a wide range of infections. These bacteria are commonly associated with various diseases, including streptococcal pharyngitis, skin infections, and post-streptococcal glomerulonephritis.

**Why the Correct Answer is Right**
Streptococcus is primarily associated with infections caused by the Lancefield grouping A and B beta-hemolytic streptococci, which are known to cause streptococcal pharyngitis and skin infections. However, group C streptococci are more commonly associated with invasive infections, such as bacteremia and pneumonia, and are less frequently linked to pharyngitis.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because group A streptococci are responsible for streptococcal pharyngitis and skin infections, making this option associated with Streptococcus.
* **Option B:** Incorrect because group B streptococci are commonly linked to neonatal sepsis and infections in pregnant women, making this option associated with Streptococcus.
* **Option D:** Incorrect because group D streptococci, also known as enterococci, can cause urinary tract infections and endocarditis, making this option associated with Streptococcus.

**Clinical Pearl / High-Yield Fact**
The Lancefield grouping system is a method used to classify beta-hemolytic streptococci based on the presence of specific antigens on their cell walls. This system is crucial for identifying the causative agent of streptococcal infections.

**Correct Answer:** C.