Microbiology · Gram-positive rods
Nocardia !
- Bacterium
- Gram-positive
- For completeness
A filamentous soil bacterium that causes lung infection and brain abscess in immunosuppressed people, and skin infection after wounds.
Updated 2026-11-01
Also called: Nocardia asteroides, Nocardia brasiliensis, Nocardia farcinica
At a glance
- Gram
- Gram-positive
- Shape
- Branching filaments that fragment
- Oxygen
- Obligate aerobe
- Family
- Nocardiaceae
- Stain
- Gram positive; weakly acid-fast (modified Kinyoun)
Morphology
- Thin Gram-positive filaments branching at right angles
- Weakly acid-fast
- Slow growth in culture
Transmission
- Inhaling soil dust
- Soil or water entering a wound
- Not considered contagious between people
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Mycolic acids in the cell wall
- Resists killing inside phagocytes
- Tendency to spread to the brain
Diseases it causes
- Pulmonary, disseminated (brain abscess) and cutaneous nocardiosis; actinomycetoma (N. brasiliensis) Nocardiosis →
Clinical picture
- Subacute pneumonia with nodules or cavities in a transplant recipient or a patient on corticosteroids
- Brain abscess
- Mycetoma: a swollen foot with sinus tracts and grains
Diagnosis
- Gram stain: branching filaments
- Modified acid-fast stain (weakly positive)
- Prolonged culture and species identification with susceptibility testing
- Brain imaging in pulmonary disease
Treatment
Sulfonamides (trimethoprim-sulfamethoxazole) are the mainstay, often combined with other antibiotics and given for months; some species such as N. farcinica are resistant, so susceptibility testing is needed. Abscesses may need drainage.
Drug class only; doses and regimens are set by the clinician from the current guideline.
Prevention
- Trimethoprim-sulfamethoxazole prophylaxis in some transplant recipients (it also prevents Pneumocystis)
- Protecting wounds from soil
Test yourself
Think of the answer, then tap the question to see it.
Which stain helps recognise Nocardia?
The modified acid-fast stain (modified Kinyoun): it is weakly positive.
Which organ should be imaged in a patient with pulmonary nocardiosis?
The brain, because it is the most common site of spread.
What is the mainstay of nocardiosis treatment?
Sulfonamides such as trimethoprim-sulfamethoxazole, guided by susceptibility testing.
Related
Related conditions
← Back to the group: Gram-positive rods
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Nocardiosis (CDC, 2024); Clinical Overview of Nocardiosis (CDC, 2024).
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Representative model, for educational purposes only.