Actinomycetes

Background

• A genetically unrelated group of Gram-positive bacilli
• Filamentous soil bacteria
• More commonly seen in fungal cultures
• Typically not acid-fast

Organisms

• Partially acid-fast (cell wall contains mycolic acid)
  • Nocardia species
  • Rhodococcus species: red colonies, associated with horses
  • Gordonia species
  • Tsukamurella species
  • Corynebacterium species
• Not partially acid-fast (cell wall does not contain mycolic acid)
  • Streptomyces species: common contaminant
  • Actinomadura species
  • Dermatophilus species
  • Nodardiopsis species
  • Oerskovia species