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2.2 Microbiology > Denise - Listeria > Flashcards

Denise - Listeria Flashcards

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1
Q

What type of bacteria is Listeria

A

Gram Positive Non-endosporing rod

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2
Q

What is the main listeria species of interest

A

L. monocytogenes

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3
Q

Describe L. monocytogenes

A

Relatively short rods
Gram positive
Catalase positive
Oxidase Negative
B-haemolytic narrow zone
Motile at 20-25 degrees but nonmotile at 37

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4
Q

Write about the pathogenicity of L. monocytogenes

A

Facultative anaerobe
Non sporulating
Psychrotrolerant
Acid tolerant
Bile salt tolerant
Can survive in food for long period
Major concern for food industry

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5
Q

How psychrotolerant is L. monocytogenes

A

Can initiate growth from -1.5 to 45 degree celsius
Can grow in fridge

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6
Q

How acid tolerant is Psychrotolerant is > monocytogenes

A

Can grow at Ph as low as 4.4

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7
Q

How salt tolerant is Listeria Monocytogenes

A

Can grow in 10 to 12% sodium chloride

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8
Q

What are the most important of the 13 Listeria monocytogenes serotypes

A

1/2 a
1/2 b
4b

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9
Q

What are the main reservoirs for L. monocytogenes

A

Animals - direct or indirect contact
Environment - soil and water
Humans - carriers in food processing environments and transmission in hospital setting (neonates)

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10
Q

Write about Listeria gastroenteritis

A

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

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11
Q

Write about Listeria epidemiology

A

22 total infection in 2018
11 were 4b
6 were 1/2a
1 was 1/2 b

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12
Q

Write about L. monocytogenes outbreaks

A

While listeriosis outbreaks attract the most attention
But most cases of human listeriosis are sporadic as it is a rare disease

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13
Q

Why is listeriosis food poisoning so difficult to tract

A

Incubation times up to 5 weeks

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14
Q

Write about the pathogenesis of listeria

A

Ingestion
Activation of PrfA

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15
Q

How does listeria cause infection

A

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

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16
Q

What are the virulence factors of listeria

A

Internalins
Listeriolysin O
Phospholipases
ActA

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17
Q

What are the two main internalins and what are they

A

InIA and InIB

Surface associated proteins

18
Q

How does InIA work

A

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

19
Q

How does InIB work

A

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

20
Q

How does InIB work

A

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

21
Q

What is listeriolysin O also called

A

B haemolysin

22
Q

Write about Listeriolysin O/B haemolysin

A

Haemolysin gene hly
Cholesterol dependent pore forming toxin
Required for survival and proliferation within macrophages and epithelial cells
Virulent strains only

23
Q

What does Listeriolysin O do

A

Disrupts phagosome
Antigenic
Oxygen labile

24
Q

What are phospholipases

A

3 different enzymes with phospholipase C activity (PLC)

PI PLC and PC PLC

Mechanical function in the escape of the phagolysome

25
Q

What is PI PLC

A

Phosphatidyl inositol-specific phospholipase C

26
Q

What is PC PLC

A

Phosphatidylcholine phospholipase C
Lecithinase

27
Q

Write about ActA

A

Surface protein that promotes polymerization of actin to form “actin tails”
Actin based intracellular motility

28
Q

What samples are there for Listeria

A

CSF
Blood

29
Q

What media is Listeria put up on

A

Listeria chromogenic agar
Fraser broth

30
Q

How is direct detection done for listeria

A

Molecular detection

31
Q

Write about listeria chromogenic agar base

A

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

32
Q

What are the basic characteristics of Listeria

A

Gram positive bacilli
KoH negative
Catalase positive
Oxidase negative
Narrow zone of B haemolysis

33
Q

What confirmatory tests are there for listeria

A

Biochemical identification
Rapid detection from culture
MALDI

34
Q

What biochemical tests are done on day 2 and 3 for listeria

A

Carbohydrate utilisation
CAMP test
Aesculin hydrolysis
Haemolysis
Motility

35
Q

Write about Listeria biochemical tests

A

Aesculin hydrolysis

Acid production without gas from glucose, maltose and salicin

No acid production from mannitol

36
Q

Write about the confirmation of listeria results

A

CSF/Blood sent to IMSRL - temple street
Irish meningitis and sepsis reference laboratory
Real time PCR directly on specimen

37
Q

Write about the confirmation of listeria results

A

CSF/Blood sent to IMSRL - temple street
Irish meningitis and sepsis reference laboratory
Real time PCR directly on specimen

38
Q

Write about the motility of listeria

A

L. monocytogenes strains are highly flagellated
Motile at low termperatures such as 30 degrees
Not motile at 37 degrees

39
Q

Write about Listeria serotyping

A

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

40
Q

How is epidemiological typing done

A

Molecular basis
WGS
Investigating foodborne disease outbreaks
Tracking strains of L. monocytogenes through the food chain and in the environment

41
Q

How is listeria treatment

A

Ampicillin
Gentamycin

2.2 Microbiology (60 decks)

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