Nocardiosis is an infection caused by Nocardia – a branching, filamentous, gram-positive bacteria found in the soil and aquatic environment – which becomes airborne and causes (most commonly) pulmonary infections. In contrast to to Actinomyces, Nocardia exhibits partial acid-fastness on staining and grows under aerobic conditions. This organism can also enter the body via ingestion and direct inoculation from trauma (ie, animal bites and thorns). Most patients with nocardiosis have some form of immunologic impairment ranging from diabetes or HIV to malignancy or immunosuppression for organ transplantation.

Nocardiosis lesions in the brain (left) and lungs (top right). Partial acid fastness on staining (bottom right). Image credit: UpToDate

Nocardia evades the destructive mechanisms of cell-mediated immunity by inhibiting lysosomal fusion (to avoid hydrolysis) and creating enzymes that alter the “oxidative burst” from neutrophils. Trimethoprim-sulfamethoxazole (TMP-SMX, or Bactrim) is the “go to” therapy for practically every manifestation of this infection. According to UpToDate, amikacin, ceftriaxone, and imipenem (often added to Bactrim in cases of CNS infection) are also used. Notable indications for surgical intervention are large abscesses refractory to antibiotics and empyema.

Remember that whenever you see unusual brain AND lung lesions, at least consider nocardiosis!

Have you ever seen Nocardia infections? Drop me a comment with your experience and questions! 🙂

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