Gram-positive, nonmotile and polymorphic acid-fast rods (0.8 μm x 1.4–1.9 μm). Forms clumps, but not cords or cross bands. Does not form spores, capsules and aerial hyphae.
Colony characteristics
Colonies are smooth and glistening with yellow-orange pigmentation (0.5–1.0 mm diameter, scotochromogenic).
Physiology
Slow growth on Löwenstein-Jensen medium or Middlebrook 7H10 agar at 31 °C (optimal temperature). No growth at 37 °C, 42 °C or 45 °C.