## **Core Concept**
Friedlander's bacillus, also known as *Klebsiella pneumoniae*, is a Gram-negative, encapsulated, non-motile rod bacterium. It is a type of bacteria that can cause various infections, particularly pneumonia. The bacterium is named after the German pathologist Carl Friedländer.

## **Why the Correct Answer is Right**
The correct answer, *Klebsiella pneumoniae*, is the bacterium referred to as Friedlander's bacillus. This organism is known for causing pneumonia, especially in individuals with compromised immune systems, and is characterized by its encapsulated form which helps in its virulence. The encapsulation is a key virulence factor that helps the bacteria evade phagocytosis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify *Klebsiella pneumoniae*.
- **Option B:** This option is incorrect as it does not correspond to *Klebsiella pneumoniae*.
- **Option D:** This option is incorrect because it is not the correct identification of Friedlander's bacillus.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that *Klebsiella pneumoniae* infections can be severe and are often associated with specific populations, such as alcoholics or those with diabetes. The bacteria can cause cavitary lesions in the lungs, which is a distinctive feature of *Klebsiella* pneumonia.

## **Correct Answer:** C. Klebsiella pneumoniae.