Listeria monocytogenes


  • A small facultative, anaerobic, catalase-positive, Gram-positive bacillus.
    • Grows well at 4-10o C. Refrigerator temperature is 4o C.[3]
    • Tumbling motility seen under light microscope at room temperature.
    • Maintain a high index of clinical suspicion for Listeria if "diphtheroids" are identified in CSF or blood because Listeria may be misidentified as Corynebacterium or Lactobacillus.
  • Widespread in nature; recovered from raw milk, soft cheeses, fruits and vegetables, processed deli meats, and undercooked fish, poultry, and meats.[4]
  • Transmission is food-borne and vertical, mother to fetus.[1]
    • Iron is important virulence factor, and iron overload is associated with enhanced susceptibility to infection
  • Immunity is predominantly cell-mediated and established via T-cell-mediated activation of macrophages.[9]
    • Cell-to-cell spread of L. monocytogenes avoids contact with extracellular environment and allows evasion of host defenses.

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Last updated: September 3, 2021