**Question:** L. monocytogenes causes a variety of diseases, including food poisoning. Listeriae are small, Gram-positive, motile rod-shaped bacteria. Which of the following best describes these microorganisms?

A. Gram-negative bacteria
B. Non-motile bacteria
C. Coccobacilli
D. Spirochetes

**Correct Answer:** C. Coccobacilli

**Core Concept:**
Listeria monocytogenes is a Gram-positive, rod-shaped bacterium belonging to the family Listeriaceae. Listeria is a genus of bacteria that includes different species, with L. monocytogenes being the most pathogenic to humans. These bacteria are characterized by their small size, Gram-positive nature, and motility. The term "coccobacilli" refers to their coccoid (cocci) and bacilli (rods) appearance, which accurately describes the morphology of L. monocytogenes.

**Why the Correct Answer is Right:**
Listeria monocytogenes exhibits a unique combination of characteristics, including Gram-positivity, rod-shaped morphology, and motility. These features make L. monocytogenes stand out among other bacteria.

**Why Each Wrong Option is Incorrect:**

A. Gram-negative bacteria: L. monocytogenes is Gram-positive, not Gram-negative.
B. Non-motile bacteria: L. monocytogenes exhibits motility due to its flagella, which is why this option is incorrect.
D. Spirochetes: L. monocytogenes is not a spirochete; it is a rod-shaped bacterium.

**Clinical Pearl:**
Understanding the distinct characteristics of Listeria species, particularly L. monocytogenes, is crucial for diagnosing infections caused by this bacterium. Infections with L. monocytogenes can lead to severe diseases, including meningitis, sepsis, and abortion in pregnant women. Prompt diagnosis and appropriate antimicrobial therapy are essential for managing these infections effectively.