Nocardia species

Nocardia species

Background:
>Nocardia species:
     1] Nocardia asteroides
     2] Nocardia brasiliensis

Nocardia: 

  • Genus of weakly staining Gram-positive, catalase-positive, rod-shaped bacteria.
  • It forms partially acid-fast beaded branching filaments (acting as fungi, but being truly bacteria).
  • Majority of strains possess the cord factor (trehalose 6-6′ dimycolate) an important virulence factor.
  • The genus includes at least 30 different species with ten of them isolated from humans. Some species are non-pathogenic while others are responsible for nocardiosis.
  • Nocardia are oral microflora found in healthy gingiva as well as periodontal pockets.
  • Most Nocardia infections are acquired by inhalation of the bacteria or through traumatic introduction.
  • Nocardia are pathogenic bacteria with low virulence:  clinically significant disease most frequently occurs as an opportunistic infection in those with a weak immune system (small children, elderly, HIV, etc).
  •  Nocardia asteroides:  species most frequently infecting humans.  Other species of medical interest are N. brasiliensis and N. caviae. Because it is acid-fast to some degree, it stains only weakly gram positive.
  • The most common form of human nocardial disease is a slowly progressive pneumonia, whose common symptoms include cough, dyspnea (shortness of breath), and fever.  Every organ can be affected if a systemic spread takes place.

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Therapy:
Important considerations:  The choice of an agent should be based on local antimicrobial sensitivities, site of infection, cost, and comorbid conditions.   Generally, the most common agents/regimens are listed first.   Listed dosages may need to be adjusted for renal dysfunction.  Specific therapy depends on the species of Nocardia.
 

  1. Bactrim (TMP-SMX) –  Mild-moderate infection:  5 to 10 mg/kg/day (based on trimethoprim component) IV/oral divided in 2-4 doses.    Severe infection: 15 to 20 mg/kg/day (based on trimethoprim component)  IV, given in equally divided doses every 6 to 8 hours.
  2. Bactrim (TMP-SMX) –  Mild-moderate infection:  5 to 10 mg/kg/day (based on trimethoprim component) IV/oral divided in 2-4 doses.    Severe infection: 15 to 20 mg/kg/day (based on trimethoprim component)  IV, given in equally divided doses every 6 to 8 hours PLUS  Imipenem 500mg IV every 6 hours.
  3. Linezolid 600 mg orally or IV q 12h  + Meropenem 0.5 – 1 gram IV q8h  (life-threatening infection -unlabeled use: 2 grams IV q8h)
  4. Imipenem 500mg IV every 6 hours + Amikacin 5 – 7.5 mg/kg/dose q8-12h (patient-specific pharmacokinetic dosing required)
  5. Minocycline 100-200 mg po bid (unlabeled use).   Usual dosage: 200 mg x 1,  followed by 100mg q12h.
  6. Ceftriaxone  +   Amikacin 5 – 7.5 mg/kg/dose q8-12h (patient-specific pharmacokinetic dosing required)
  7. Cefotaxime 1-2 grams IV q4-12h.  (Moderate to severe: 1-2 grams q8h.  Life-threatening: 2 grams IV q4h)   PLUS  Amikacin 5 – 7.5 mg/kg/dose q8-12h (patient-specific pharmacokinetic dosing required)
Nocardia species