**Question:** Rapid growing non-tuberculous mycobacteria causing lung infection are all except:

A. M. fortuitum
B. M. abscessus
C. M. chelonae
D. M. kansasii

**Core Concept:** Rapid growing non-tuberculous mycobacteria (NTM) are a group of mycobacteria that can cause infections in humans, particularly in immunocompromised individuals. These infections are distinct from those caused by Mycobacterium tuberculosis (TB), which are typically slow growing.

**Why the Correct Answer is Right:** The correct answer is D. M. kansasii because it is generally considered the slowest growing of the rapid growing NTM. While M. fortuitum, M. abscessus, and M. chelonae are indeed rapid growing NTM, M. kansasii is slower and less common in causing lung infections.

**Why Each Wrong Option is Incorrect:**

A. M. fortuitum: This bacterium is considered one of the fastest growing NTM and is more likely to cause lung infections.
B. M. abscessus: Another fast-growing NTM, M. abscessus is more likely to cause lung infections than M. kansasii.
C. M. chelonae: This bacterium is also among the faster growing NTM and is more commonly associated with lung infections.

**Why Each Wrong Option is Incorrect:**

A. M. fortuitum: This bacterium is considered one of the fastest growing NTM and is more likely to cause lung infections.
B. M. abscessus: Another fast-growing NTM, M. abscessus is more likely to cause lung infections than M. kansasii.
C. M. chelonae: This bacterium is also among the faster growing NTM and is more commonly associated with lung infections.

**Clinical Pearl:** Knowledge of the growth rate of NTM is crucial in diagnosing and treating NTM lung infections, as slower growing species may be overlooked if rapid tests are used exclusively. Rapid growing species like M. fortuitum, M. abscessus, and M. chelonae should raise suspicion for NTM lung infections, while slower growing species like M. kansasii are more likely to be misdiagnosed if not considered in the differential diagnosis.

**Why Each Wrong Option is Incorrect:**

A. M. fortuitum: This bacterium is considered one of the fastest growing NTM and is more likely to cause lung infections.
B. M. abscessus: Another fast-growing NTM, M. abscessus is more likely to cause lung infections than M. kansasii.
C. M. chelonae: This bacterium is also among the faster growing NTM and is more commonly associated with lung infections.

**Why Each Wrong Option is Incorrect:**

A. M. fortuitum: This bacterium is considered one of the fastest growing NTM and is more likely to cause lung infections.
B. M. abscessus: Another fast-growing NTM,