Mycoplasma pneumoniae

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Bacteria - Gram Indeterminate

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Mycoplasma pneumoniae

Characteristics
- Pleomorphic
- No cell wall
  - Cell membrane contains cholesterol
  - Not visualizable by Gram stain
  - Not susceptible to beta-lactam antibiotics
- Grows on Eaton agar
Transmission
- Respiratory droplets
- Occurs frequently in young (<30 y.o.) individuals living in close contact
  - College students, military recruits, and prisoners
Presentation
- atypical “walking pneumonia”
  - Insidious onset, fever, headache, nonproductive cough
  - Caused by tracheobronchitis: inflammatory infiltration of airways
  - patchy/diffuse interstitial infiltrate on CXR
    - CXR looks worse than patient presentation would suggest
- Associated with
  - Cold agglutinins
    - IgM antibodies agglutinate RBCs under cold temperatures
      - Due to similarity between antigens in Mycoplasma and RBC membranes (molecular mimicry)
    - Causes hemolytic anemia
      - Complement-mediated attack of RBCs with bound IgM
      - Presents with positive Coombs test, elevated LDH, elevated reticulocyte count
      - Spontaneous resolution over time
  - Erythema multiforme (EM)
    - Red rash that can evolve into target lesions
      - Caused by autoimmune response to antigens deposited in skin
  - Stevens-Johnson syndrome
  - Culture-negative endocarditis
Treatment
- Macrolides
- Doxycycline
- Fluoroquinolone
  - Respiratory fluoroquinolones used like levofloxacin or moxifloxacin
- Penicillin ineffective since it has no cell wall