Listeria monocytogenes Flashcards
how many of the 17 species in the Listeria genus are pathogenic
2: Listeria monocytogenes, Listeria ivanovii (pathogenic in cows)
characteristics of Lm?
- gram positive
- psychrotrophic
- facultative anaerobic
- nonsporulating
- motile
- small rod
- displays motility via its flagella; temperature dependent, motile between 20-30C
what genetic techniques were once used to characterize Lm? what is the main technique now?
genetic finger printing or serotyping
the main technique used today is whole genome sequencing
how many serotypes of Lm are there?
13
what have the 13 serotypes of Lm been characterized into?
4 evolutionary lineages and 63 clonal complexes (CCs)
how old are Lm’s sub-lineages? what did this observation lead to?
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
how does Lm live in the environment?
lives ubiquitously in the environment as a saprophyte. it can survive for long periods in soil, food plants, and water
besides animals and humans, what has Lm also been found to infect?
protozoa
true or false: some humans carry Lm without symptoms
true, either in the intestine or the gall bladder
what temperatures can Lm grow and divide at?
4-45C; it grows in the refrigerator and outcompetes other bacteria in this environment
true or false: Lm can grow in a pH as low as 4.4
true
true or false: Lm can grow in high salt concentrations as high as 10%
true; and heat resistance increases as salt content decreases
what is Lm sensitive to?
pasteurization
when can Lm survive pasteurization?
when its in the white blood cell
under what conditions can Lm survive in, on environments like hot dogs, bologna, and ham?
lower temperatures and high salt conditions
why is listeria so problematic when established in a food-processing plant?
it can persist for years, due to forming a biofilm which is basically impossible to get rid of
what parts of a food-processing plant is listeria often detected in?
in moist areas such as floor drains, stagnant water, and processing equipment
lowering the temperature doesnt stop Lm growth but …
it does slow it
what is the most common source of Lm
raw milk
what does pasteurization do?
reduces the number of Lm cells in milk to levels that do not pose a risk to human health
which two groups of people should not eat raw milk cheeses?
pregnant women and immuno-compromised people
what kind of meats offer Lm a good environment to grow in?
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
high risk foods for Lm?
deli meats and hot dogs (not re-heated)
high fat dairy products, raw dairy products, pate and meat spread, soft unripened cheese, smoked seafood
general info on Listeria infections:
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
cell biology of the infection process:
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).
what kind of bacterial pathogen is Lm?
an intracellular bacterial pathogen that can be taken up by non-phagocytic cells, such as epithelial cells, or phagocytic cells
what is the cell biology of the infection process regarding epithelial cells?
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
what is Listeriolysin O capable of?
- 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
What are goblet cells?
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
what is the cell biology of the infection process regarding goblet cells?
- 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
what is the cell biology of the infection process regarding SLAPs?
- 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
what are trophoblasts?
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
what is the cell biology of the infection process regarding trophoblasts?
- 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
what is the interaction of Lm with the microbiota?
- 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
how does virulence gene regulation work with Lm?
- 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
at low temperatures, how is promoter PrfA affected? how does it operate in the host when its at a temperature of 37C?
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
What are the prevention methods for Lm?
- 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
