Card Set Information

2013-10-08 23:13:21
Listeria medical microbiology listeriosis gram positive rods monocytogenes catalase actin polymerization hemolysin hemolysis septicemia meningitis

Epidemiology, pathogenesis, clinical significance, laboratory identification, treatment and prevention.
Show Answers:

  1. General characteristics of Listeria
    • Morphology - slender, gram-positive rods that do not form spores
    • Avid intracellular parasites that reside in the cytoplasm of infected cells.
    • Destinguished from Corynebacterium and Streptococcus because it exhibits tumbling motility and is catalase-positive
    • Asymmetric actin polymerization as motility
    • Salt tolerant and can survive and grow at temps below 1°C
  2. Epidemiology of Listeria
    • Listeria monocytogenes - only species affecting humans
    • Other Listeria species widespread in nature
    • Causes Listerosis - sproadic cases or small epidemics, typically foodborne.
    •         - processed dairy, ground meats, poultry, deli meats.
    • Grows at 4°C - presents issue for food storage in refrigerators and factories.
    • Infections most common in pregnant women, fetuses and newborns, the elderly and immunocompromised individuals.
  3. Pathogenicity of Listeria
    • Facultative intracellular parasite,
    • Attaches and enters cells by normal phagocytic mechanisms.
    • Escapes phagocytic vacuole using listeriolysin O.
    •      -mutants lacking this hemolysin are avirulent.
    • Low pathogenicity (infects mostly immunocompromised and is not transmitted via direct contact), but high virulence (once infected, it is very hard to get rid of and has a high incidence of disease).
  4. Transmission of Listeria from one cell to another
    • After escaping the phagolysosome with the use of listeriolysin O the bacteria multiplies inside the cytoplasm of the macrophage.
    • The bacteria polymerize the actin fibers of the host cell in order to propel itself across the cell and into the neighboring cell.
      Phospholipase C (hemolysin) is used to penetrate the double membrane vacuole once inside a new neighboring cell, thus avoiding the cells of our immune system
  5. Clinical significance of L. monocytogenes
    • Septicemia and meningitis are most commonly reported listeriosis.
    • Pregnant women may exhibit flu like symptoms and it can be passed to the baby both systemically and via asymptomatic vaginal infection.
    •      - Common cause of newborn meningitis and spontaneous abortion.
  6. Laboratory Identification of L. monocytogenes
    • May be isolated from blood, CSF and other specimens
    • On Blood Agar - produces small colonies surrounded by narrow β-hemolysis.
    • Motile, catalase positive, gram positive rod
  7. Treatment and prevention of L. monocytogenes
    • A variety of antibiotics are effective.
    •      - Ampicillin, trimethoprim/sulfamethoxazole

    Prevention accomplished by proper food handling and prep procedures.