8 - Listeria monocytogenes Flashcards
Typical Listeriosis outbreak:
hot dogs (make sure you cook your hot dogs)
What are the 2 species of Listeria that are pathogenic:
- Listeria monocytogenes (humans)
- Listeria Ivanovii (cows)
Characteristics of Lm:
- gram +
- psychrotrophic
- facultative anaerobe
- nonsporulating
- motile small rods
it displays motility via its:
flagella
Motility is temperature dependent; it is motile between _________
20-30C
There are 13 serotypes of Lm though 95% of outbreaks are caused by:
1/2a, 1/2b, 4b
Which lineages are responsible for most infections?
Lineage 1 and Lineage 2
*Lineage 1 has affinity for the brain/placenta (serious / deadly)
Lineage 1 Lm appears to be more virulent, as these CCs appear to have trophism for :
the nervous system and the placenta
Listeria is a young/old pathogen?
young
T OR F: Lm may have emerged as a pathogen relatively recently potentially in association with the increased movement of humans, animals, and food
T
Lm is an almost ubiquitous environmental ________________
saprophyte
T OR F: Some humans carry Lm without symptoms (either in the intestine or gall bladder)
T
It can grow and divide from 4-45C, it grows in the _______________ and outcompetes other bacteria in this environment
refrigerator
It can grow in media as low as pH ___ and in salt contents as high as ____
4.4
10
*hurdle concept: heat resistance increases as salt content decreases
Is Listeria sensitive to pasteurization temperatures?
Yes
When Listeria is inside a _______ it can survive pasteurization
white blood cell
Why does Listeria persist for years once established in a food-processing plant?
because it has the ability to form biofilms
What happens to Listeria when you lower the temperature ?
It doesn’t stop Lm growth but it does slow it
Explain why raw milk cheeses are a source of Lm?
Raw milk cheeses are unpasteurized , Lm survives well during cheese manufacturing due to both the temperature (cold) as well as the salt content (high) - while many of its competitors die
T OR F: it is recommended for pregnant women and those who are immuno-compromised to eat raw milk cheeses
F
Contamination of animal muscle can happen ________ or ________ slaughter
during or after
Explain why cold-meats / ready-to-eat meats are a good source of Lm:
These meats are heated and then cooled in brine
Listeria infection is ___________ but mortality is ___________
uncommon
high
What are the main symptoms associated with Listeria for healthy people vs immunocompromised people:
- most individuals will experience mild gastroenteritis
- immunocompromised/ pregnant women will experience sepsis, meningitis, infection of the fetus leading to abortion or other pregnancy complications
What is the infection process / route followed by Listeria
1) you ingest Lm from contaminated food
2) you absorb it in your intestine
3) goes to the lymph node
4) goes to liver/spleen
5) goes to brain/placenta
In the liver _____ cells phagocytose Lm cells and they succumb to necroptosis
Kupffer
The lymph and blood can also carry Lm to the ________________
blood-brain barrier
Lm is an ______________ bacterial pathogen and can be taken up by non-phagocytic cells, such as epithelial cells, or phagocytic cells
intracellular
How does Lm infect epithelial cells?
1) Lm enters epithelial cells through receptor-mediated endocytosis
2) InlA and InlB bind to the cell receptors E-cadherin and Met
3) Once inside the host cell, Lm uses LLO and phospholipase A and B for vacuole rupture and escape
* Lm can also polymerize actin and use this to become motile to spread laterally from cell to cell
What are goblet cells?
They are specialized epithelial cells that line mucosal surfaces and have a role in barrier maintenance through the secretion of mucus
How does Lm infect goblet cells?
1) In goblet cells lnlA binds to E-cadherin which leads to receptor clustering, E-chaderin phosphorylation and ubiquitylation and subsequent bacterial up-take by the cell
2) In goblet cells, Lm remains internalizaed in the vacuole and rapidly transcytoses through the cell
How does Lm infect macrophages?
1) Macrophages are phagocytic cells which actively phagocytize Lm cells
2) In macrophages, Lm can replicate in spacious listeria containing phagosome (SLAPs)
3) In SLAPs, Lm expresses intermediate levels of LLO which inteferes with the pH gradient that is required for acidification of the phagosome - but is not enough to promote phagosomal rupture
Trophoblasts are cells that will form the ________, which are derived from the fetal tissue and form the external layer of the developing blastocyst in the context of pregnancy
placenta
How does Lm infect trophoblasts ?
1) in trophoblasts InlB binds Met and induces phosphorylation and ubiquitylation and receptor-mediated endocytosis
T OR F: In the intestinal lumen Lm encounters other bacteria that belong to the microbiome
T
Lm produces a _____________ known as listeriolysin S (LLS) that restricts the growth of common commensals such as Allobaculum, Streptococcus, Alloprevotella
bacteriocin
The core Lm virulon is regulated by the _____ promoter
PrfA
If the loop is present, prfA will be _________
weakly active
T OR F: Lm is a very serious food-borne infection which can result in systemic infection, meningitis or encephalitis and abortion in pregnant females
T
Lm is an intracellular disease and can cross 3 important barriers:
- the intestinal barrier
- the blood brain barrier
- the placental barrier
Are the virulence factors of listeria well conserved or constently changing?
well conserved
