USMLE

Listeria monocytogenes

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Bacteria - Gram Positive
  1. Staph aureus: Overview
  2. Staph aureus: Presentation
  3. Methicillin-Resistant Staph aureus (MRSA)
  4. Staph saprophyticus
  5. Strep pneumoniae: Overview
  6. Strep pneumoniae: Presentation
  7. Strep viridans
  8. Strep pyogenes: Overview
  9. Strep pyogenes: Presentation
  10. Strep agalactiae
  11. Strep bovis
  12. Enterococcus
  13. Bacillus anthracis
  14. Bacillus cereus
  15. Clostridium tetani
  16. Clostridium perfringens
  17. Clostridium botulinum
  18. Clostridium difficile
  19. Corynebacterium diphtheriae
  20. Listeria monocytogenes
  21. Nocardia
  22. Actinomyces

Listeria monocytogenes 

  • Characteristics
    • Gram + rod
    • Facultative intracellular
    • Grows well in cold temperatures (“cold-enrichment”)
      • Can grow at refrigeration temperatures (4-10 degrees C)
    • Tumbling motility under light microscopy
      • Forms “rocket tails” via actin polymerization, which enhance intracellular movement and cell-to-cell spread
  • Transmission
    • Acquired by ingestion of unpasteurized dairy products and cold deli meats
      • Listeria is found in GI tract and milk of cows
  • Presentation
    • Infections occur in individuals with weak cellular immunity
      • Neonates < 3 months old
        • May be transmitted transplacentally or by vaginal transmission during birth
      • Immunocompromised individuals
        • e.g. HIV patients, organ transplant recipients, and individuals with certain malignancies.
      • Elderly
      • Pregnant women
    • Meningitis 
      • CSF obtained via LP will demonstrate WBCs and gram-positive bacilli.
      • Contrast w Neisseria meningitidis: gram stain would show gram-negative diplococci 
    • Febrile gastroenteritis
      • Most often seen in healthy individuals
    • Sepsis
    • May present as spontaneous abortion in pregnant women
  • Treatment       
    • Ampicillin
      • Ampicillin is first-line for treatment of Listeria, which is resistant to cephalosporins.
    • TMP-SMX (second line)