Listeria

CASE 1

• A 26 year old woman in the 30th week of gestation develops a brief episode of diarrhea followed by high fever and sepsis. A physical examination at the time of hospitalization was unrevealing except for a temperature of 38.9. Multiple cultures were obtained but none were positive after 3 days. The patient was treated empirically with a combination of broad-spectrum antibiotics.

• The patient is of French origin and regularly consumes sliced, cured meats with lunch and soft cheeses (Camembert and Brie) with dinner.

• On the third hospital day, the patient miscarried. On the sixth hospital day, a blood culture grew pleiomorphic Gram-positive bacilli. Antimicrobial therapy was changed to high-dose, intravenous ampicillin, and the patient improved gradually.

Questions:

1. Why did this woman develop Listeriosis? From what source did she most likely acquire the organism? What microbiological feature of Listeria makes these sources so prominent?
2. What other age groups are particularly susceptible to severe Listeria infection?
3. Apart from generalized sepsis, what other focal infection does Listeria commonly cause in susceptible patients?
4. How does Listeria evade the immune system?
5. Listeria is an intracellular pathogen. How does the organism spread from one cell to an adjacent cell? What virulence factors are required for this cell-to-cell transfer.