Swarming growth is shown by which gram positive bacilli: September 2009
**Core Concept**
Swarming growth is a characteristic growth pattern exhibited by certain bacteria, where they grow rapidly and uniformly over a surface, often forming a distinct edge or "swarm." This phenomenon is typically observed in gram-positive bacilli with specific virulence factors and enzymes.
**Why the Correct Answer is Right**
The correct answer is correct because swarming growth is a hallmark of *Proteus mirabilis*, a gram-positive bacillus that produces a cocktail of enzymes, including proteases, lipases, and gelatinases. These enzymes break down the extracellular matrix, allowing the bacteria to move rapidly and uniformly over surfaces, leading to the characteristic swarming growth pattern. The production of these enzymes is mediated by the *proU* operon, which is activated in response to environmental stimuli.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because *Bacillus anthracis*, while a gram-positive bacillus, does not exhibit swarming growth. Instead, it forms a characteristic "medusa head" or "chain of sausages" morphology.
* **Option B:** This option is incorrect because *Clostridium difficile*, a gram-positive bacillus, does not exhibit swarming growth. It is known for its role in causing antibiotic-associated diarrhea and colitis.
* **Option C:** This option is incorrect because *Corynebacterium diphtheriae*, a gram-positive bacillus, does not exhibit swarming growth. It is known for its role in causing diphtheria.
**Clinical Pearl / High-Yield Fact**
Swarming growth is an important characteristic in identifying *Proteus mirabilis*, which is often isolated from urinary tract infections and is known for its ability to cause urinary tract stones.
**Correct Answer:** C. *Proteus mirabilis*