**Question:** Which of the following organisms' culture shows the phenomenon 'satellitism'?

A. Mycobacterium tuberculosis
B. Pseudomonas aeruginosa
C. Escherichia coli
D. Salmonella typhi

**Core Concept:**

Satellitism is a rare phenomenon observed in certain bacterial cultures where a satellite colony develops around a primary colony. This can be seen during the growth of certain bacteria on agar plates. The primary colony represents the main organism, while the satellite colony represents a secondary, less virulent strain or a bacteriophage infecting the primary strain.

**Why the Correct Answer is Right:**

The correct answer, B. Pseudomonas aeruginosa, is known to exhibit satellitism due to the presence of bacteriophages. Pseudomonas aeruginosa is a gram-negative bacillus commonly found in environments like soil, water, and air. These bacteriophages can infect the primary P. aeruginosa colony, forming the satellite colony.

**Why Each Wrong Option is Incorrect:**

A. Mycobacterium tuberculosis is responsible for tuberculosis, a lung disease caused by the infection with Mycobacterium species. It does not exhibit satellitism.

C. Escherichia coli (E. coli) is a common gram-negative bacterium found in the human gut. It does not exhibit satellitism.

D. Salmonella typhi is responsible for typhoid fever caused by Salmonella enterica serovar Typhi. It does not exhibit satellitism.

**Clinical Pearl:**

Understanding satellitism helps in identifying the presence of bacteriophages and their interaction with bacterial colonies, which can be relevant in clinical settings. For example, it can indicate the presence of opportunistic infections in immunocompromised patients or suggest the involvement of bacteriophages in antibiotic resistance mechanisms. However, satellitism is not a definitive diagnostic tool but can provide important clues for further investigation and management of the case.