Listeria monocytogenes

Question 1

What kind of bacteria is L.monocytogenes (7 characteristics)?

Answer 1

1. gram positive
2. bacillius
3. non-spore forming
4. psychrotroph class
5. facultatviely anerobic (can grow aerobically or anaerobically depending on the presence of oxygen)
6. motile
7. grow well on complex media like blood agar plates (BAPS)

Question 2

What are 3 physical characteristics of the growth of L.monocytogenes?

Answer 2

1. grow over a wide range of temperatures 3-42 degrees
2. grow over wide pH range (less than 5.5 - 9.5)
3. grow in high concentrations of NaCl (up to 10%)

Question 3

Where is listeria’s normal habitat?

Answer 3

usually found in soil and animal intestine through contamination

Question 4

How is listeria presented in animals?

Answer 4

• CNS infections [goats, cattle]

- septic abortions

Question 5

How is listeria presented in man?

Answer 5

• food borne disease
• CNS infections/Death [listeria induced meningitis]
• spontaneous abortion in pregnant mothers

Question 6

How does listeria cause disease (pathogenesis)?

Answer 6

through ingestion of contaminated foods
- listeria makes its way to the intestine, and attaches to macrophages in the intestinal tract; proteins on the surface of the bacteria will induce the host cells to actively take up the listeria (cells in the intestine will develop a high affinity for it), then the bacteria breaks out of its membrane bound compartment (phagolysosome) in the host cell by using listerolysin & then produces two other hemolysins to destroy cell membranes and latch onto actin in the cytoskeleton of the host cell; it then uses the actin to propel itself onto the neighboring cell

• listeria has intracellular and extracellular growth

Question 7

What kind of clinical infections can listeria cause in humans?

Answer 7

meningitis, encephalitis (infection of brain tissue) and septicemia (sepsis)

Question 8

Who are most at risk for listeria?

Answer 8

elderly, immunocompromised people, and pregnant women (can cause a influenza-like illness that can result in abortion or stillbirth)

Question 9

What is the incubation period for listeria [how long it stays “dormant”]?

Answer 9

as long as 2 months

Question 10

what is the mortality percentage for CNS infections caused by listeria?

Answer 10

20-50% because its difficult to diagnose this type of meningitis

Question 11

How is listeria transmitted?

Answer 11

fecal-oral
and in foods like coleslaw, soft unpasteurized cheeses, turkey wieners, cold cuts, mushrooms and prepackaged salads, milk …etc…

Question 12

How many cases of listeria are fatal?

Answer 12

1/3 of cases even with proper antibiotics

Question 13

How many invasive cases is listeria involved in each year in the US?

Answer 13

approx. 1700

Question 14

What are two reasons why listeria is hard to track?

Answer 14

1. it has a long incubation period

2. underreporting [seems like food poisoning]

Question 15

How do we treat listeria?

Answer 15

theres currently no vaccine so the only way is to use antibiotics but only when the infection is diagnosed in time