Which Mycobacterium produces an orange pigment and is most commonly recovered from water?

Which Mycobacterium produces an orange pigment and is most commonly recovered from water?

• A. M. intracellulare
• B. M. gordonae
• C. M. asiaticum
• D. M. kansasii

Answer: (B)

Pigment production patterns in non-tuberculous mycobacteria help identify environmental species. Some produce pigment in the dark (scotochromogens), others only after light exposure (photochromogens), and some do not pigment at all. M. gordonae is a classic scotochromogen that yields an orange pigment even without light and is famously recovered from water supplies, hence the nickname tap water bacillus. That combination—orange pigment and frequent isolation from water—fits best. The other species have different pigment behavior or aren’t as commonly associated with water sources, so they don’t align as well with this clue.

Pigment production patterns in non-tuberculous mycobacteria help identify environmental species. Some produce pigment in the dark (scotochromogens), others only after light exposure (photochromogens), and some do not pigment at all. M. gordonae is a classic scotochromogen that yields an orange pigment even without light and is famously recovered from water supplies, hence the nickname tap water bacillus. That combination—orange pigment and frequent isolation from water—fits best. The other species have different pigment behavior or aren’t as commonly associated with water sources, so they don’t align as well with this clue.