Listeria monocytogenes

Question 1

how many of the 17 species in the Listeria genus are pathogenic

Answer 1

2: Listeria monocytogenes, Listeria ivanovii (pathogenic in cows)

Question 2

characteristics of Lm?

Answer 2

• gram positive
• psychrotrophic
• facultative anaerobic
• nonsporulating
• motile
• small rod
• displays motility via its flagella; temperature dependent, motile between 20-30C

Question 3

what genetic techniques were once used to characterize Lm? what is the main technique now?

Answer 3

genetic finger printing or serotyping

the main technique used today is whole genome sequencing

Question 4

how many serotypes of Lm are there?

Answer 4

13

Question 5

what have the 13 serotypes of Lm been characterized into?

Answer 5

4 evolutionary lineages and 63 clonal complexes (CCs)

Question 6

how old are Lm’s sub-lineages? what did this observation lead to?

Answer 6

50-150 years. observation lead to a hypothesis that Lm may have emerged as a pathogen relatively recently potentially in association with the increased movement of humans, animals, and food

Question 7

how does Lm live in the environment?

Answer 7

lives ubiquitously in the environment as a saprophyte. it can survive for long periods in soil, food plants, and water

Question 8

besides animals and humans, what has Lm also been found to infect?

Answer 8

protozoa

Question 9

true or false: some humans carry Lm without symptoms

Answer 9

true, either in the intestine or the gall bladder

Question 10

what temperatures can Lm grow and divide at?

Answer 10

4-45C; it grows in the refrigerator and outcompetes other bacteria in this environment

Question 11

true or false: Lm can grow in a pH as low as 4.4

Answer 11

true

Question 12

true or false: Lm can grow in high salt concentrations as high as 10%

Answer 12

true; and heat resistance increases as salt content decreases

Question 13

what is Lm sensitive to?

Answer 13

pasteurization

Question 14

when can Lm survive pasteurization?

Answer 14

when its in the white blood cell

Question 15

under what conditions can Lm survive in, on environments like hot dogs, bologna, and ham?

Answer 15

lower temperatures and high salt conditions

Question 16

why is listeria so problematic when established in a food-processing plant?

Answer 16

it can persist for years, due to forming a biofilm which is basically impossible to get rid of

Question 17

what parts of a food-processing plant is listeria often detected in?

Answer 17

in moist areas such as floor drains, stagnant water, and processing equipment

Question 18

lowering the temperature doesnt stop Lm growth but …

Answer 18

it does slow it

Question 19

what is the most common source of Lm

Answer 19

raw milk

Question 20

what does pasteurization do?

Answer 20

reduces the number of Lm cells in milk to levels that do not pose a risk to human health

Question 21

which two groups of people should not eat raw milk cheeses?

Answer 21

pregnant women and immuno-compromised people

Question 22

what kind of meats offer Lm a good environment to grow in?

Answer 22

ready-to-eat meats that are then cooled in brine, since competing bacteria are reduced. if listeria contamination can happen after heating there will be a major problem

Question 23

high risk foods for Lm?

Answer 23

deli meats and hot dogs (not re-heated)

high fat dairy products, raw dairy products, pate and meat spread, soft unripened cheese, smoked seafood

Question 24

general info on Listeria infections:

Answer 24

Lm infection is uncommon but the mortality rate is high (20-30%)

most individuals will experience mild gastroenteritis, however, children, the elderly, immunocompromised people, and pregnant women will experience sepsis, meningitis, infection of the fetus leading to abortion or other pregnancy complications

Question 25

cell biology of the infection process:

Answer 25

contaminated food goes into the intestine, travels to the lymph node, enters the bloodstream where they then go into the liver and spleen and replicate. in the liver, the kupffer cells phagocytose Lm cells and then succumb to necroptosis (a programmed cell death process, which generates inflammatory signals and typically occurs during infection).
monocytes that are then called to the inflammatory regions can travel up to the brain and the placenta (if its a pregnant women).

Question 26

what kind of bacterial pathogen is Lm?

Answer 26

an intracellular bacterial pathogen that can be taken up by non-phagocytic cells, such as epithelial cells, or phagocytic cells

Question 27

what is the cell biology of the infection process regarding epithelial cells?

Answer 27

1) Lm enters non-phagocytic cells through receptor-mediated endocytosis
2) requires Internal A and Internal B to bind to the cell receptors E-cadherin and Met (receptor for hepatocyte growth factor (HGF)), respectively
3) once inside the host cell, Lm uses listeriolysin O (LLO) and two phospholipases, phospholipase A and PlcB for vacuole rupture and escape

• Lm can survive and divide within the cytosol of the host cell and induce changes in the host cell
• Lm can also polymerize actin and use this to become motile to spread laterally from cell to cell

Question 28

what is Listeriolysin O capable of?

Answer 28

• causes changes in the mitochondrial morphology and function
• affects the endoplasmic reticulum by increasing ER stress
• causes permeabilization of the cell due to its pore forming activity

Question 29

What are goblet cells?

Answer 29

specialized epithelial cells that line mucosal surfaces and have a role in barrier maintenance through the secretion of mucus

goblet cells are also part of the innate immunity and secrete anti-microbial proteins, chemokines, and cytokines

goblet cells also form goblet cell associated antigen passages to deliver luminal substances to the underlying lamina propria (LP) antigen-presenting cells to induce adaptive immune responses

Question 30

what is the cell biology of the infection process regarding goblet cells?

Answer 30

• in goblet cells Internal A binds to E-cadherin which leads to receptor clustering, E-cadherin phosphorylation and ubiquitylation and subsequent bacterial uptake by the cell
• in goblet cells, Lm remains internalized in the vacuole and rapidly transcytoses through the cell

Question 31

what is the cell biology of the infection process regarding SLAPs?

Answer 31

• macrophages are phagocytic cells which actively phagocytize Lm cells
• Lm can be replicated in spacious Listeria containing phagosomes (SLAPs)
• SLAPs Lm expresses intermediate levels of LLO which interferes with the pH gradient that is required for acidification of the phagosome- but is not enough to promote phagosomal rupture

Lm can be considered both a vacuolar and cytosolic bacterium

Question 32

what are trophoblasts?

Answer 32

cells that will form the placenta, which are derived from the fetal tissue and form the external layer of the developing blastocyst in the context of pregnancy

Question 33

what is the cell biology of the infection process regarding trophoblasts?

Answer 33

• InlB binds Met and induces phosphorylation and ubiquitylation and receptor-mediated endocytosis
• binding of soluble InlB to the complement component (C1QBP) facilitates receptor clustering and helps to speed bacterial uptake

Question 34

what is the interaction of Lm with the microbiota?

Answer 34

• in the intestinal lumen Lm encounters other bacteria that belong to the microbiome
• Lm produces a bacteriocin known as listeriolysin S (LLS) that restricts the growth of common commensal such as Alloprevotella, Allobaculum and Streptococcus

Question 35

how does virulence gene regulation work with Lm?

Answer 35

• the core Lm virulon is regulated by the PrfA promoter
• genes controlled by this promoter are located on the Listeria pathogenecity island, as well as on three other PrfA regulated loci
• these genes include all the genes necessary for intracellular invasion and vacuole escape (InlA, InlB, ActA, LLO, plcA, and plcB)
• PrfA is also under its own regulation, which causes a positive feedback loop to regulate the expression of these genes under infection conditions

Question 36

at low temperatures, how is promoter PrfA affected? how does it operate in the host when its at a temperature of 37C?

Answer 36

weak transcription of PrfA generated from promoter directly in front of the prfA gene. transcripts are not translated due to a secondary structure that hides access for the ribosome

in the host, the leader RNA sequence is broken down which results in rapid translation of several inactive transcripts. upon entry into the cytosolic compartment an unknown cofactor binds to PrfA and increases its affinity for its target sequence. this results in more synthesis of more PrfA

Question 37

What are the prevention methods for Lm?

Answer 37

• pregnant women, the elderly, people with weakened immune systems and young children should avoid:
  
  • deli meats (unless they are dried, salted, or heated until steaming hot)
  • pate and meat spreads, unless they are frozen, canned, or shelf-stable
  • raw or undercooked meat, poultry and fish
  • hot dogs unless they are heated until steaming hot
  • raw or unpasteurized dairy products including semi-soft cheese
  • refrigerated smoked seafood and fish

avoid drinking pasteurized milk
before cutting a melon, thouroughly wash and scrub the entire melon with warm water using a clean produce brush