The Runyon classification of nontuberculous mycobacteria based on the rate of growth, production of yellow pigment and whether this pigment was produced in the dark or only after exposure to light.[1]
It was introduced by Ernest Runyon in 1959.[2]
On these bases, the nontuberculous mycobacteria are divided into four groups:
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The first three groups are classified as "Slowly growing Mycobacteria".
Runyon I organisms (photochromogens) are slow growing, and produce a yellow-orange pigment when exposed to light. Mycobacterium kansasii, Mycobacterium marinum
Runyon II organisms (scotochromogens) are slow growing, and produce a yellow-orange pigment in light or in the dark. Mycobacterium scrofulaceum, Mycobacterium gordonae, Mycobacterium szulgai