Which mycobacterial species is commonly considered a nonpathogenic environmental contaminant and often forms brown colonies on egg-based media?

Which mycobacterial species is commonly considered a nonpathogenic environmental contaminant and often forms brown colonies on egg-based media?

• A. Mycobacterium avium complex
• B. Mycobacterium gordonae
• C. Mycobacterium tuberculosis
• D. Mycobacterium kansasii

Answer: (B)

The main idea is distinguishing an environmental, nonpathogenic mycobacterium from disease-causing ones by its typical lab behavior. Mycobacterium gordonae is famously known as a nonpathogenic environmental contaminant, frequently recovered from water sources, and it often forms brown pigmented colonies on egg-based media. This pigmented, contaminant-associated profile on such media makes it the classic clue that labs use to recognize Gordonae rather than a pathogenic mycobacterium. In contrast, the other organisms are associated with true human disease and are not described as common environmental contaminants with brown pigment on egg-based media. For example, the tuberculosis complex organism is pathogenic and not typically identified by brown pigment as a contaminant pattern, while the other listed species can cause disease in certain hosts and contexts, not merely appear as a routine environmental contaminant on egg-based media.

The main idea is distinguishing an environmental, nonpathogenic mycobacterium from disease-causing ones by its typical lab behavior. Mycobacterium gordonae is famously known as a nonpathogenic environmental contaminant, frequently recovered from water sources, and it often forms brown pigmented colonies on egg-based media. This pigmented, contaminant-associated profile on such media makes it the classic clue that labs use to recognize Gordonae rather than a pathogenic mycobacterium.

In contrast, the other organisms are associated with true human disease and are not described as common environmental contaminants with brown pigment on egg-based media. For example, the tuberculosis complex organism is pathogenic and not typically identified by brown pigment as a contaminant pattern, while the other listed species can cause disease in certain hosts and contexts, not merely appear as a routine environmental contaminant on egg-based media.