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, Mycobacterium asiaticum
Runyon II organisms (scotochromogens) are slow growing, and produce a yellow-orange pigment in light or in the dark. Some become darker with exposure to light. Mycobacterium scrofulaceum, Mycobacterium gordonae, Mycobacterium szulgai, Mycobacterium xenopi, Mycobacterium celatum, Mycobacterium flavescens
Runyon III organisms are slow growing, and do not produce pigment. Note that some may produce very pale yellow, buff, or tan pigment but do not intensify upon light exposure. Mycobacterium avium-intracellulare, Mycobacterium terrae, Mycobacterium paratuberculosis, Mycobacterium shimoidae, Mycobacterium genavense
Runyon IV organisms are rapid growing for mycobacteria (colonies in 5 days). They do not produce pigment. Mycobacterium fortuitum, Mycobacterium peregrinum, Mycobacterium abscessus, Mycobacterium chelonae, Mycobacterium thermoresistible
Some rapidly growing mycobacteria are considered "late-pigmenting".[3]
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