Scotochromogens

Scotochromogens

These mycobacteria are characterized by their ability to produce yellow, orange, or red pigmented colonies on the LJ medium even when incubated in dark (Fig. 42-1, Color Photo 45). These species are widely distributed in the environ-ment. Mycobacterium scrofulaceum, Mycobacterium gordonae, and Mycobacterium szulgai are the important species.

      M. scrofulaceum causes infection localized to lymphatictissues and is responsible for causing scrofula or cervical adenitis in children. Morphologically, on staining, the bacil-lus shows short or long filaments. It is sensitive to cycloser-ine, but resistant to INH.

      M. gordonae rarely causes pulmonary disease. It is oftenfound as a contaminant in tap water, hence called tap water scotochromogen. This is also found as a contaminant in clinical specimens. M. gordonae does not hydrolyze urea, nicotinamide, and pyrazinamide; in this respect, it differs from M. scrofulaceum.

      M. szulgai occasionally may cause pulmonary disease andbursitis. It is a scotochromogen when grown at 37°C and photochromogen when grown at 27°C.