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The Timpe and Runyon classification of nontuberculous mycobacteria is 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.

It was introduced by Ernest Runyon in 1959.

On these bases, the nontuberculous mycobacteria are divided into four groups:

Slowly growing Mycobacteria

The first three groups are classified as "Slowly growing Mycobacteria".

Runyon I: Photochromogens

Runyon I organisms (photochromogens) are slow growing, and produce a yellow-orange pigment when exposed to light. The group includes Mycobacterium kansasii, Mycobacterium intermedium, Mycobacterium marinum, Mycobacterium asiaticum, and Mycobacterium simiae. Mycobacterium szulgai is a photochromogen when grown at 24 degrees, and a scotochromogen at 37 degrees. In contrast, Runyon classifications III through IV are considered nonphotochromogens, in that exposure to light does not make them produce pigment which they would not develop in dark growing conditions.

Runyon II: Scotochromogens

Runyon II organisms (scotochromogens) are slow-growing and produce a yellow-orange pigment regardless of whether they are grown in the dark or the light. The group includes Mycobacterium scrofulaceum and Mycobacterium gordonae, among others. Mycobacterium szulgai is a scotochromogen when grown at 37 degrees, as mentioned above.

Runyon III: Nonchromogens

Runyon III organisms (nonchromogens) are slow-growing and never produce pigment, regardless of culture conditions. The group includes Mycobacterium avium and Mycobacterium intracellulare (together known as the MAC complex), Mycobacterium tuberculosis, Mycobacterium ulcerans and numerous other organisms. Mycobacterium xenopi is also a nonchromogen.

Runyon IV: Rapid Growers

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 thermoresistibile, Mycobacterium smegmatis.

Some rapidly growing mycobacteria are considered "late-pigmenting".

References

1. Rogall T, Wolters J, Flohr T, Böttger EC (October 1990). "Towards a phylogeny and definition of species at the molecular level within the genus Mycobacterium". International Journal of Systematic Bacteriology. 40 (4): 323–30. doi:10.1099/00207713-40-4-323. PMID 2275850.
2. Runyon EH (January 1959). "Anonymous mycobacteria in pulmonary disease". The Medical Clinics of North America. 43 (1): 273–90. doi:10.1016/S0025-7125(16)34193-1. PMID 13612432.
3. Koneman, Elmer W. (1988). Color atlas and textbook of diagnostic microbiology. Philadelphia: Lippincott Williams & Wilkins. p. 560. ISBN 9780397508259. Runyon has termed these organisms nonphotochromogenic, meaning that exposure to light does not make the pigment more intense.
4. Brown-Elliott BA, Wallace RJ (October 2002). "Clinical and taxonomic status of pathogenic nonpigmented or late-pigmenting rapidly growing mycobacteria". Clin. Microbiol. Rev. 15 (4): 716–46. doi:10.1128/cmr.15.4.716-746.2002. PMC 126856. PMID 12364376.

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