Nocardia

MICROBIOLOGY

• Gram-positive branching, beaded, filamentous rod.
  • Partially acid fast with modified Kinyoun stain.
  • Can be difficult to recover; notify lab if high index of suspicion.
  • Grow on non-selective media in 2-14 days.
    • Selective media (Thayer-Martin, paraffin agar, charcoal-buffered yeast extract media) may be needed to enhance growth and minimize contaminants.
• More than 50 species known. Found worldwide, considered a soil pathogen. May also be seen in human oral flora.
  
  • Many of the isolates initially identified as N. asteroides are now known by modern techniques to have been misclassified.
• Classified by some according to drug-susceptibility patterns + other organisms/groups:
  • Type I: N. abscessus
  • Type II: N. brevicatena/paucivorans complex
  • Type III: N. nova complex (including N. nova, N. veterana, N. africana)
  • Type IV: N. transvalensis complex
  • Type V: N. farcinica
    • Most common cause of disseminated/extrapulmonary disease
  • Type VI: N. cyriacigeorgica
  • N. brasiliensis
    • Cause of primary cutaneous infection in immunocompetent hosts
  • N. pseudobrasiliensis 
  • N. otitidiscaviarum