This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
. Swarming growth on culture is characteristic of which Gram-negative organism? 
Select and explain. 
A. Clostridium welchii, B. Clostridium tetani, C. Bacillus cereus, D. Proteus mirabilis
D: Proteus mirabilis
Answer: D: Proteus mirabilis 
Explanation: Ans. is 'd' i.e., Proteus mirabilis Swarmin growth . Swarming growth is due to motility of bacteria. . In young culture discrete colonies are seen but thereafter actively motile cells spread on the surface of the plate in successive waves to form a thin filmy layer in concentric circles.