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Nocardia

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Nocardia spp. 

  • Characteristics
    • Gram + rod with branching filaments
      • Forms long, branching filaments resembling fungi
      • Note: Actinomyces is also gram + filamentous rod
    • Partially acid-fast
      • Weakly pink with Ziehl-Neelsen stain, meaning that it resists the acid-mediated removal of stain (hence, acid-fast)
      • Contrast vs.  Actinomyces - not acid fast 
    • Aerobic
      • Contrast vs. Actinomyces - anaerobic
    • Catalase + 
      • Increased risk of infection in patients with chronic granulomatous disease
    • Found in soil
    • Urease +
  • Risk factors 
    • Immunocompromised individuals
      • Inhalation of bacteria causes pulmonary infection
      • E.g. chronic steroid use,  HIV infection
    • Trauma
      • Direct contact via skin break can infect immunocompetent individuals
  • Presentation
    • Pulmonary cavitary lesions
      • Most common in immunocompromised patients
      • Mimics tuberculosis but with negative PPD
      • Contrast vs. Actinomyces, which presents with oral/facial abscesses 
    • Cutaneous infections
      • Usually after trauma in immunocompetent individuals
      • Presents as cellulitis or painful lymphadenopathy
  • Treatment
    • Trimethoprim-sulfamethoxazole (TMP-SMX)
      • First-line treatment 
    • Carbapenems used in patients with sulfa allergies