Nocardiosis: Nocardia asteroides Complex

Question 1

Classify Nocardia asteroides

Answer 1

Gram +

Bacillis with branching beaded (coccobacillary) filaments (hyphae)

Saprophytic (soil normal flora, water environment)

Aerobic actinomycetes

Acid-fast staining (weakly)

Question 2

How is nocardia transmitted?

Answer 2

1) Inhalation (primary route)
2) Cutaneously through an open skin wound exposed to soil (rare)

**Not transmitted person to person and is not nocoscomial

Question 3

How does nocardia cell walls differ from mycobacteria (like TB)

Answer 3

Nocardia have shorter-chained (40- to 60-carbon) mycolic acids.

Hence, they are weakly acid-fast staining

Question 4

Describe the 2 virulence factors of nocardia:

Answer 4

1) Catalase + superoxide dismutase: protects nocardia from neutrophil/macrophage attack
2) Trehalos 6-6’ dimycolate (cord factor): prevents formation of the phagolysosome

Question 5

What is the most common presenting disease of nocardia?

What kind of patients get infected?

Answer 5

Commonly presents as pulmonary disease.

Nocardiosis is an opportunistic disease, so patients with underlying debilitating factors get infected most often.

• -most commonly in chronic lung disease patients
• -also in immunocompromised, corticosteroid use, diabetes, AIDS, hematological probs

Question 6

Do nocardia form granulomas?

Answer 6

No.

They produce acute inflammatory responses with necrotic abscess formation.

Question 7

There are 3 different syndromes of nocardiosis. What are they?

Answer 7

1) Pulmonary nocardiosis (pneumonia-like symptoms)
2) Cerebral nocardiosis (HA, confusion, seizures)
3) Cutaneous nocardiosis (ulcers)

Question 8

How can you tell between pulmonary nocardiosis versus typical S. pneumonia infection??

Answer 8

Abscess formation and dissemination of nocardia from lungs to produce cerebral and cutaneous nocardiosis.

• *remember, nocardiosis will likely be in immunocompromised patients
• *initial diagnosis is hard since they have similar symptoms

Question 9

How do you diagnose nocardiosis?

Answer 9

1) Smear/culture on BCYE (yeast extract and act. charcoal)
2) Gram stain –> look for beaded, branching filaments
3) Acid-fast stain
4) Various biochemical tests that a lab will do for me so I shouldn’t have to memorize all of them.

Question 10

What is the vaccine for nocardia called?

Answer 10

Trick question. There isn’t a vaccine.

Question 11

How do you treat nocardiosis?

Answer 11

1) Trimethoprim-sulfamethoxazole (Septra) –> sulfa drugs!
2) If complicated, give Sulfonamide, ceftriaxone, and amikacin.

**Must give at least 6 months in IC person, at least 12 months in IC populations

Question 12

BONUS: If you give TMP-SMZ to a person with G6PD deficiency, what could happen??

Answer 12

Hemolysis.

–sulfa drugs are oxidizing. G6PD deficient patients cannot metabolize sulfas well via reduction, so the cells lyse.