Epidemiology

Etiology

• Pathogen: Listeria monocytogenes; a gram-positive, catalase-positive, rod-shaped, facultative intracellular, motile bacterium
• Route of transmission
  • Acquired listeriosis: ingestion of contaminated food (listeria can grow in temperatures as low as -1.5 ºC)
    • Raw milk products
    • Raw and smoked meat/fish
    • Industrially processed vegetables such as ready-made salads
  • Congenital listeriosis
    • Transplacental transmission during pregnancy
    • Perinatal transmission (via infected vaginal secretions)
• Incubation time: 1–90 days (usually within a month)
• Risk factors
  • Immunodeficiency
  • Age > 60
  • Pregnancy
  • Neonates

Pathophysiology

• Listeriolysin O: This major virulence factor generates pores in phagosome membranes, which allows phagocytosed L monocytogenes to escape into the cytoplasm of monocytes and avoid lysosomal destruction.
• Actin-based transcellular spread: The organism hijacks the actin-based cellular motility mechanism of host cells, which allows it to spread to adjacent cells without reentering the extracellular space. This significantly reduces exposure of L monocytogenes to antibodies and phagocytic cells.
• Because of these adaptations, antibody- and phagocyte-mediated destruction of the pathogen is impaired; therefore, infections are controlled primarily by the cytotoxic T-cell response.

Clinical features

• Healthy adults: self-limiting gastroenteritis (watery diarrhea)
• Pregnant women
  • Flu-like illness
  • Chorioamnionitis
  • Spontaneous abortion
  • Sepsis
• Infants
  • Neonatal meningitis
  • Sepsis
    • Respiratory distress, temperature instability within the first few hours of life
  • Granulomatosis infantiseptica

Diagnostics

Treatment

Ampicillin is the treatment of choice for Listeria, which is not sensitive to cephalosporins.