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Encapsulated Bacteria

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Topic updated on 08/01/15 6:31pm

Overview
  • Most important encapsulated bacteria and fungi ("SHiN Kills Some Patients with Capsules")
    • Streptococcus pneumoniae
    • Haemophilus influenzae type B (B polysaccharide)
    • Neisseria meningitidis
    • Klebsiella pneumoniae 
    • Salmonella typhi
    • Pseudomonas aeruginosa
    • Cryptococcus neoformans
      • only encapsulated fungal pathogen
  • Other encapsulated bacteria
    • Bordetella pertussis
    • Escherichia coli
      • meningeal strains only
    • Bacillus anthracis
      • contains poly D-glutamate capsule
    • Streptococcus pyogenes
      • anti-phagocytic, non-immunogenic capsule
Physiology
  • Quellung reaction
    • antibodies bind to capsule
    • used to visualize
      • S. pneumoniae
      • H. influenzae
      • N. meningitidis
      • K. pneumoniae
  • Capsules serve as antigen in vaccines
    • H. influenzae type B vaccine
    • meningococcal vaccines
    • S. pneumoniae vaccine (pneumovax)
  • Capsules act as antiphagocytic virulence factors
  • Encapsulated bacteria can generally
    • cause meningitis
    • produce IgA protease
    • undergo transformation
      • take up DNA from their environment
  • Opsonization
    • antibodies bind to capsule to aid phagocytosis by macrophages and neutrophils
    • clearance of these pathogens depends on presence of C3 complement and a funcitonal spleen 


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(M1.MC.75) A 23-year-old male is involved in a motorcycle accident and is brought to the nearest level 1 trauma center. On arrival, the patient's vitals are T: 37 deg C, HR: 102 bpm, BP: 105/60, RR: 12, SaO2: 100%. A FAST exam is performed during the initial workup which demonstrates significant free fluid in the abdomen (Figure A). An abdominal CT scan is subsequently obtained which demonstrates a grade V splenic laceration (Figure B) and the patient is emergently brought to the operating room where a splenectomy is successfully performed. Following surgery, this patient will be at increased risk of infection with which of the following organisms? Topic Review Topic
FIGURES: A   B        

1. Legionella
2. S. aureus
3. Shigella dysenteriae
4. K. pneumoniae
5. Chlamydia

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