## Core Concept
The question tests the knowledge of bacterial motility, which is an important characteristic used in the identification and classification of bacteria. Motility in bacteria is often determined by the presence or absence of flagella. Non-motile bacteria lack flagella or have structures that do not enable them to move.

## Why the Correct Answer is Right
The correct answer, *Klebsiella pneumoniae*, is a non-motile Gram-negative bacterium. This characteristic is significant in clinical microbiology for differentiating it from other bacteria. *Klebsiella pneumoniae* is known to cause various infections, including pneumonia, and is often identified in the laboratory by its non-motility, among other features.

## Why Each Wrong Option is Incorrect
* **Option A:** *Escherichia coli* is generally motile, with peritrichous flagella that enable it to move. Its motility is a key characteristic used in its identification.
* **Option B:** *Proteus spp.* are known for their swarming motility on agar plates, which is a distinctive feature of these bacteria.
* **Option D:** *Salmonella Typhi* is also motile, possessing peritrichous flagella.

## Clinical Pearl / High-Yield Fact
A useful clinical pearl is that *Klebsiella pneumoniae* is often associated with severe community-acquired pneumonia, especially in individuals with certain risk factors like alcoholism or diabetes. Its non-motility can aid in its identification.

## Correct Answer: C. Klebsiella pneumoniae