<prompt> Pigment producing atypical mycobacteria ?M. foution and M. chelonaeM. xenopi and MACM. gordonae and M. szulgaiM. ulcerans  <response>: Ans. is c i.e., M. gordonae and M. szulgai Non-tubercular mycobacteria also called atypical mycobacteria have been classified into four groups by Runyon based on pigment production and rate of growth. 1 Group I photochromogens :- These produce pigmented colonies yellow-orange only when exposed to light, but not in dark. Examples of photochromogens are M. asiaticum, M. kansasii, M. marinum, and M. simiae. 2 Group II scotochromogens :- These always produce pigmented colonies yellow-orange-red, i.e. in dark as well as in light. Scotochromogens are M. flovescens, M. gordonae, M. scrofulaceum and M. szulgi. 3 Group HI Nonchromogens :- These do not produce pigment. Nonchromogens are M. avium complex MAC, M. haemophilum, M. gastri, M. ulcerans, M. xenopi and M. nonchromogenicum. 4 Group IV rapid growers :- This is heterogeneous group of mycobacteria capable of rapid growth, colonies appearing within 7 days of incubation. Within the group, photochromogenic, scotochromogenic and nonchromogenic species occur. Chromogenic pigment producing rapid growers are mostly saprophytic, e.g. M. phlei and M. smegmetis. M. fouitum and M. chelonei do not produce any pigment. Other rapid growers are M. abscessus, M. vaccae, M. genevense, M. confluentis, and M. intermedium. 