USMLE

Nocardia

951 views
Bacteria - Gram Positive
  1. Staph aureus: Overview
  2. Staph aureus: Presentation
  3. Methicillin-Resistant Staph aureus (MRSA)
  4. Staph saprophyticus
  5. Strep pneumoniae: Overview
  6. Strep pneumoniae: Presentation
  7. Strep viridans
  8. Strep pyogenes: Overview
  9. Strep pyogenes: Presentation
  10. Strep agalactiae
  11. Strep bovis
  12. Enterococcus
  13. Bacillus anthracis
  14. Bacillus cereus
  15. Clostridium tetani
  16. Clostridium perfringens
  17. Clostridium botulinum
  18. Clostridium difficile
  19. Corynebacterium diphtheriae
  20. Listeria monocytogenes
  21. Nocardia
  22. Actinomyces

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