Lecture 8-Listeria Monocytogenes

Question 1

Listeria monocytogenes?

Answer 1

• only one out of 6 species that is pathogenic to humans
• gram positive, psychrotrophic, faculative anaerobic, nonsporulating, motile, small rod
• displays motility via its flagella
• motile between 20-30C
• survive for long periods in soil, food plants, and water
• it can grow and divide from 4-45C, it grows in the refrigerator and outcompetes other bacteria in this envrionment
• sensitive to pasteurization temp, but when inside a WBC, it can survive pasteurization
• lowering the temp increases Lm survival in high salt environments
• grows easily in hot dogs, bologna, ham

Question 2

can low temperatures kill listeria monocytogenes

Answer 2

-lowering the temp doesn’t stop the Lm growth but it does slow it

Question 3

What should not be recommended to pregnant women and immuno-compromised individuals?

Answer 3

• should not eat raw milk, cured meats because listeria monocytogenes easily grow in these foods d/t favorable conditions
• any ready-to-eat foods that are served without cooking or processing

Question 4

What is used to delineate Lm outbreaks?

Answer 4

PFGE (the pulsed-field gel electrophoresis process)

Question 5

What are some problems that can arise from PFGE?

Answer 5

• over-dicrimination: when PFGE patterns differ for two strains which are the same (most commonly caused by the loss of a mobile genetic element)
• under-discrimination: when PFGE patterns are the same for two strains which are different

Question 6

Who is at high risk of listeriosis?

Answer 6

• not a problem for immunocompetent hosts

- problem for the very young, old, transplant patients, cancer patients, HIV/AIDS, pregnant women

Question 7

What is the incubation time for listeria monocytogenes?

Answer 7

Incubation times can be up to 5 wks which makes outbreaks hard to define

Question 8

Virulence Factor Internalin A and INIB

Answer 8

mediate attachment and bacterial invasion into the host’s intestinal cells
This attachment signals to the cell to up-take the attached listeria cell into a vacuole

Question 9

Listerolysin 0 (LLO) and PI-PLC virulence factors

Answer 9

dissolved the vacuole containing listeria cells

-when cells are free in the cytoplasm, they divide freely, protected from the innate immune system

Question 10

ActA virulence factors

Answer 10

• expressed only on the non-dividing side of the listeria cell (which provides directional movement)
• polymerizes host cell actin and allows the listeria cell to move through the host cell and protrude into neighboring cells
• the vacuoles are now double walled which is digested by LLO (listerolysin O) and the process starts again

Question 11

Which barriers is listeria monocytogenes able to cross? (3)

Answer 11

1. the intestinal barrier
2. the blood brain barrier
3. the placental barrier

Question 12

Is the Lm genome conserved?

Answer 12

Yes, highly conserved

• There is little horizontal gene transfer, and there are few mutations to the genome that are vertically transferred as well
• strong conservation of genome organization

Question 13

What do Lm form that gives them the ability to persist in food processing environments for years?

Answer 13

Lm have the ability to form biofilms in factories