An isolate from sputum of a patient with chronic cavitary lung disease produces colonies that develop bright yellow pigment only after exposure to light for 24 hours. Colonies kept in the dark remain buff coloured. Which organism fits this pattern?
- A Mycobacterium avium complex
- B Mycobacterium fortuitum
- C Mycobacterium kansasii ✓
- D Mycobacterium xenopi
Correct answer: C. Mycobacterium kansasii
Explanation
Photochromogens (Runyon Group I) form colonies that turn yellow only after light exposure due to photoinduced carotenoid production; M. kansasii is the classic example and mimics pulmonary TB. M. avium complex is a non-chromogenic slow grower, M. xenopi is a scotochromogen whose pigment develops even in darkness, and M. fortuitum is a rapid grower, all failing the light-dependent pigment criterion.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.