• Aerobic Gram-positive rods that form thin branching filaments.
  • Widespread in the environment.
  • N. asteroides is the important human pathogen, although other species can cause infection.


  • Infection is acquired from the soil by the airborne route.
  • Outbreaks of infection in renal transplant units have been associated with local building work.
  • Actinomycetoma is acquired by implantation of organisms into wounds and progressive destruction of skin, fascia, bone and muscle.


N. asteroides is an opportunist pathogen infection in immunocompromised patients; primarily a pulmonary infection, but secondary spread to form abscesses in brain or kidney is common. N. brasiliensis can also cause actinomycetoma.

Laboratory Diagnosis:

  • Gram stains of pus may reveal Gram-positive filaments or rods.
  • Sulphur granules not seen.
  • Grows as ‘breadcrumb’ colonies on blood agar within 2-10 days’ incubation.
  • Often acid-fast.