- A small facultative, anaerobic, catalase-positive, Gram-positive bacillus.
- Grows well at 4-10o C. Refrigerator temperature is 4o C.
- 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.
- Transmission is food-borne and vertical, mother to fetus.
- 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.
- Cell-to-cell spread of L. monocytogenes avoids contact with extracellular environment and allows evasion of host defenses.
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