USMLE

Bordetella pertussis

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Bacteria - Gram Negative
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Bordetella pertussis

  • Characteristics
    • Gram negative coccobacillus
    • Aerobic
      • Colonizes mucosal surfaces with high oxygen content (e.g. lungs, airway)
  • Virulence factors
    • Pertussis toxin (an exotoxin)
      • activates adenylate cyclase by inhibiting Gi 
        • Increased intracellular cAMP leads to increased secretion of sodium, chloride, and water (edema), which impairs phagocytosis, allowing the bacteria to survive
      • Similar mechanism to Bacillus anthracis edema factor 
    • Tracheal cytotoxin  
      • Kills epithelial cells (cytotoxin) in airways, which impairs mucociliary escalator from clearing respiratory secretions
  • Disease
    • Infants are especially at risk
      • <6 months old – too young to vaccinate
      •  Unvaccinated children
    • 3 stages
      • Catarrhal
        • low-grade fevers and runny nose (coryza)
      • Paroxysmal
        • Causes whooping cough
          • paroxysms of intense cough followed by inspiratory “whoop” (gasp for air)
          • Technically a form of acute bronchitis
          • Severe coughing may cause vomiting (posttussive emesis)
      • Convalescent
        • Gradual recovery of bronchitis and cough
  • Prevention
    • Tdap, DTaP vaccines
      • The acellular pertussis vaccine currently available in the U.S. contains purified components of Bordetella pertussis and detoxified pertussis toxin (toxoid)
  • Diagnosis
    • Bordetella PCR and serology is the gold standard
      • Unlikely to be tested, given that this is too obvious
      • requires nasopharyngeal secretions on a special swab, as the bacteria will not grow on cotton
    • Culture in Bordet-Gengou agar
    • Modified Regan-Lowe medium selective for Bordetella
    • May be mistaken as viral infection due to lymphocytic infiltrate resulting from immune response
  • Treatment 
    • Macrolides
      • TMP-SMX may be used if allergic to macrolides