Listeria monocytogenes

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Listeria monocytogenes
History

• 1926 isolated form rabbits with mononucleosis

• 1927 given its name to honor surgeon lord Lister

• 1929 isolated from human with mononucleosis-like
  disease

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Listeria monocytogeneshabitat

• Found in soil, vegetation, water and GI tract of
  animals
• Disease risk
• fetus
• Neonate
• malignancy
• immunocompromised

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Morphology/Physiology

• Gram-positive coccobacilli
• Short chains

• b-hemolytic on blood agar

• blue-green translucent colonies on colorless
  media observed with obliquely reflected light

• Can grow and replicate at 4o C

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Natural hosts
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Neonatal Disease

• Mother has no symptomatic illness
• Granulomatosis infantiseptica - infection of
  fetus in utero
• can lead to abortion, disease at birth (sepsis,
  pneumonia, fetal distress, seizures, rash,
  abscesses, and granulomas
• High mortality rate
• Exposure on vaginal delivery
• can result in meningitis or meningoencephalitis
  with sepsis within 2-3 weeks

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Adult Disease

• Septicemia following ingestion
• Meningitis
• leading cause of bacterial meningitis in patients
  with cancer and in renal transplant patients
• Common organism in HIV infected patients

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Frequency of symptoms and mortality
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Virulence Properties

• ?-hemolysin (listeriolysin O), lecithinase and
  phospholipase
• produced by virulent strain only
• oxygen labile
• antigenic
• disrupts phagocytic vacuole

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Virulence Properties

• Intracellular Growth

• bacterium escapes from host vacuole
• undergoes rapid division
• becomes encapsulated by short actin filaments
• facilitates movement to periphery with protrusion
  and then penetration to neighboring cells
• never exposed to humoral immunity

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Cell-cell transmission
Entry
Escape

• Fusion with another cell

actin tail
replication
extrusion
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Treatment

• Penicillin or ampicillin alone or in combination
  with gentamicin
• Protection is with activation of macrophages