GENUS NOCARDIA:
Characteristics:
- 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.
Transmission:
- 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.
Diseases:
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.
