MICROBIOLOGY

• Gram-positive branching, beaded, filamentous rod.
  • Partially acid-fast with modified Kinyoun or Ziehl-Neelsen stain.
  • It can be difficult to recover; notify the lab if there is a high index of suspicion.
  • Grows on non-selective media in 2-14 days.
    • Selective media (Thayer-Martin, paraffin agar, and charcoal-buffered yeast extract media) may be necessary to enhance growth and minimize contamination.
  • Molecular diagnostics exist; culture remains the gold standard.
• More than 50 species are known. Found worldwide, considered a soil pathogen. It may also be seen in human oral flora.
  
  • Many of the isolates initially identified as N. asteroides are now known, through modern techniques, to have been misclassified.
• Individual species are associated with unique drug-susceptibility profiles (see below).