Some mycobacteria produce a yellowish pigment, with some species doing so only in light.
Production of yellow pigment in the light: photochromogen
Production of yellow pigment in the dark: scotochromogen
Specimen: mycobacterial isolate on 2 culture tubes or plates
Parameters:
(1) appearance after being incubated in the dark at 37°C
(2) appearance after being incubated in the light at 37°C
There are 3 possible combinations of these findings.
Incubated in Dark
Incubated in Light
Mycobacterial Species
pigmented
M. scroulaceum, M. gordonae, M. flavescens, M. xenopi, M. szulgai
not pigmented
M. kansasii, M. marinum, M. simiae, M. asiaticum
M. tuberculosis, M. bovis, M. ulcerans, M. fortuitum, M. chelonae, classic M. avium
where:
• The light exposed culture of M. szulgai should be incubated at 25°C.
• Some members of the M. avium complex produce pigment.
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Specialty: Clinical Laboratory
