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Listeria monocytogenes

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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)