Denise - Listeria Flashcards
What type of bacteria is Listeria
Gram Positive Non-endosporing rod
What is the main listeria species of interest
L. monocytogenes
Describe L. monocytogenes
Relatively short rods
Gram positive
Catalase positive
Oxidase Negative
B-haemolytic narrow zone
Motile at 20-25 degrees but nonmotile at 37
Write about the pathogenicity of L. monocytogenes
Facultative anaerobe
Non sporulating
Psychrotrolerant
Acid tolerant
Bile salt tolerant
Can survive in food for long period
Major concern for food industry
How psychrotolerant is L. monocytogenes
Can initiate growth from -1.5 to 45 degree celsius
Can grow in fridge
How acid tolerant is Psychrotolerant is > monocytogenes
Can grow at Ph as low as 4.4
How salt tolerant is Listeria Monocytogenes
Can grow in 10 to 12% sodium chloride
What are the most important of the 13 Listeria monocytogenes serotypes
1/2 a
1/2 b
4b
What are the main reservoirs for L. monocytogenes
Animals - direct or indirect contact
Environment - soil and water
Humans - carriers in food processing environments and transmission in hospital setting (neonates)
Write about Listeria gastroenteritis
Contaminated food source
Oral entry route
Colonisation of the intestine
Intestinal translocation - replication in liver and spleen
Resolution or haematogenous spread to other organs
Immunocompetent symptoms include enteritis or a febrile flu-like condition
Write about Listeria epidemiology
22 total infection in 2018
11 were 4b
6 were 1/2a
1 was 1/2 b
Write about L. monocytogenes outbreaks
While listeriosis outbreaks attract the most attention
But most cases of human listeriosis are sporadic as it is a rare disease
Why is listeriosis food poisoning so difficult to tract
Incubation times up to 5 weeks
Write about the pathogenesis of listeria
Ingestion
Activation of PrfA
How does listeria cause infection
Entry into macrophage
Uptake by macrophage and incorporation into phagolysosome
Escape from phagolysosome
Replication
Actin tail allows movement into other cells via
Extrusion via filopods
Enters other cell
What are the virulence factors of listeria
Internalins
Listeriolysin O
Phospholipases
ActA
What are the two main internalins and what are they
InIA and InIB
Surface associated proteins
How does InIA work
Binds to E-cadherin on host epithelial cells
Role in adherence and invasion
Responsible for uptake into epithelial cells is required for crossing the intestinal and placental barriers
Intestinal and placental barriers
How does InIB work
Mediates entry into a variety of cell types and plays a role in invading human placenta in conjunction with InIA
Binds to Met on host cells
How does InIB work
Mediates entry into a variety of cell types and plays a role in invading human placenta in conjunction with InIA
Binds to Met on host cells
Role in invasion
BBB or CSF
What is listeriolysin O also called
B haemolysin
Write about Listeriolysin O/B haemolysin
Haemolysin gene hly
Cholesterol dependent pore forming toxin
Required for survival and proliferation within macrophages and epithelial cells
Virulent strains only
What does Listeriolysin O do
Disrupts phagosome
Antigenic
Oxygen labile
What are phospholipases
3 different enzymes with phospholipase C activity (PLC)
PI PLC and PC PLC
Mechanical function in the escape of the phagolysome
What is PI PLC
Phosphatidyl inositol-specific phospholipase C
What is PC PLC
Phosphatidylcholine phospholipase C
Lecithinase
Write about ActA
Surface protein that promotes polymerization of actin to form “actin tails”
Actin based intracellular motility
What samples are there for Listeria
CSF
Blood
What media is Listeria put up on
Listeria chromogenic agar
Fraser broth
How is direct detection done for listeria
Molecular detection
Write about listeria chromogenic agar base
Peptones/salts/chromogenic substrate/lithium chloride/antibiotics
Listeria species growth in blue colonies (halo around L. monocytogenes)
The lipase is responsible for the opaque white halo which surrounds L. monocytogenes
B-glucosidase is common to all listeria species giving the colonies their blue
What are the basic characteristics of Listeria
Gram positive bacilli
KoH negative
Catalase positive
Oxidase negative
Narrow zone of B haemolysis
What confirmatory tests are there for listeria
Biochemical identification
Rapid detection from culture
MALDI
What biochemical tests are done on day 2 and 3 for listeria
Carbohydrate utilisation
CAMP test
Aesculin hydrolysis
Haemolysis
Motility
Write about Listeria biochemical tests
Aesculin hydrolysis
Acid production without gas from glucose, maltose and salicin
No acid production from mannitol
Write about the confirmation of listeria results
CSF/Blood sent to IMSRL - temple street
Irish meningitis and sepsis reference laboratory
Real time PCR directly on specimen
Write about the confirmation of listeria results
CSF/Blood sent to IMSRL - temple street
Irish meningitis and sepsis reference laboratory
Real time PCR directly on specimen
Write about the motility of listeria
L. monocytogenes strains are highly flagellated
Motile at low termperatures such as 30 degrees
Not motile at 37 degrees
Write about Listeria serotyping
For epidemiological purposes
Listeria possess group-specific surface proteins
Somatic (O) antigens
Flagellar (H) antigens
1/2a, 1/2b and 4 b are responsible for 98% of documented human listeriosis cases
Serotypes 4a and 4c are rarely associated with outbreaks of the disease
How is epidemiological typing done
Molecular basis
WGS
Investigating foodborne disease outbreaks
Tracking strains of L. monocytogenes through the food chain and in the environment
How is listeria treatment
Ampicillin
Gentamycin
