BACTERIA · Gram-positive filamentous, partially acid-fast
Nocardia spp.
Nocardia — Modified Ziehl-Neelsen (weakly acid-fast)
Stain: Modified Ziehl-Neelsen / Kinyoun stainMorphology: Beaded, branching filamentous gram-positive rods that are weakly/partially acid-fastYield: MEDIUMDifficulty: MEDIUM
Image: Wikimedia Commons (CC BY 4.0)
Key facts
**Pathogenesis**: Soil-dwelling obligate aerobe; inhalation in immunocompromised hosts (chronic steroids, transplant, HIV) causes cavitary pneumonia with hematogenous spread to brain. **Diagnostic clue**: Weakly acid-fast (vs Mycobacterium = strongly acid-fast; vs Actinomyces = NOT acid-fast and anaerobic); branching filaments. Cavitary pneumonia + brain abscess in immunocompromised. **Virulence**: Catalase, superoxide dismutase resist macrophage killing.
Boards buzzwords
- partially acid-fast
- branching filaments
- soil aerobe
- immunocompromised lung
- brain abscess
- cavitary pneumonia
Associated diseases
- Cavitary pneumonia (immunocompromised)
- Brain abscess (hematogenous)
- Cutaneous nocardiosis (gardeners)
Treatment
TMP-SMX (high-dose) first-line; add imipenem ± amikacin or linezolid for CNS / severe disease; prolonged course (6–12 months)
Related organisms
Listeria monocytogenes
Gram-positive rod (facultative intracellular)
Mycobacterium tuberculosis
Acid-fast bacillus (mycolic acid cell wall)
Treponema pallidum
Spirochete
Mycobacterium leprae
Acid-fast bacillus (obligate intracellular)
Neisseria meningitidis
Gram-negative diplococci
Borrelia burgdorferi
Spirochete