FREDERIC B.ASKINMDWILLIAM H.WESTRAMD
The genus Mycobacterium consists of rod-shaped, obligate aerobes known for their slow growth and resistance to destaining by acid alcohol treatments (acid-fast). Mycobacterium tuberculosis is the best known and most virulent Mycobacterium species. Nontuberculous or atypical mycobacteria are a heterogeneous group of organisms sharing many cellular features with M tuberculosis, while maintaining distinct enzymatic and mycolic acid patterns. Atypical mycobacteria are classified into 4 groups.1 Group I is composed of photochromogens, which are found in the central region of the United States. Group II consists of the scotochromogens, which most commonly occur in the Great Lakes region. Both groups derive pigment from β-carotene; with light exposure, photochromogens become yellow, while scotochromogens transition from yellow to orange. Group III is composed of the nonchromogens, which are found most often in the southeastern region of the United States. Group IV consists of the rapid or variable growers, which are ubiquitous across all regions of the country.
Pathology Quiz Case 1: Diagnosis. Arch Otolaryngol Head Neck Surg. 2002;128(12):1426-1427. doi: