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)

An important way to differentiate environmental Mycobacteria is by pigment production and where they are commonly found. Orange pigment in culture points to scotochromogenic mycobacteria, which produce pigment in the dark. Among these, Mycobacterium gordonae is the classic species frequently recovered from water supplies and often considered a contaminant rather than a true pathogen. Its orange pigment appears without needing light exposure, and its prominence in tap water makes it the best match for an organism described as producing orange pigment and being commonly recovered from water. The other species are more often linked to clinical disease in humans or differ in their pigment response and environmental sources.