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MIIM20002 - Microbes, Infections, Responses > Lecture 30 - Legionella > Flashcards

Lecture 30 - Legionella Flashcards

1
Q

Where does the causative agent of Legionaire’s disease come from?

A

Environment
• soil
• water

No human or animal reservoir

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2
Q

Describe Legionnaire’s disease

A

Acute form of pneumonia

- requires serious medical intervention

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3
Q

What is Pontiac fever?

A

Milder form of Legionnaire’s disease
• flu like
• self limiting

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4
Q

What determines whether the infection causes Legionnaire’s or Pontiac fever?

A

Unclear
• patient factors?
• strain?

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5
Q

How many species of Legionella are there?

A

more than 50

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6
Q

Which is the most common species of Legionella?

A

Legionella pneumophila

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7
Q

Which serogroup is the most common cause of Legionnaire’s disease?

A

Serogroup 1

90 % of cases

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8
Q

Why is it an emerging pathogen

A

Only been identified from the late 1970’s

Only recently has it caused outbreaks, due to man-made water systems

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9
Q

Describe the Gram classification of Legionella

A

Gram negative

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10
Q

Describe the trends of Legionnaire’s disease in AUstralia

A

Not very common
• only a few cases reported
• since most people clear the infection

2000
• very large outbreak at Melbourne Aquarium

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11
Q

Describe the result of most cases of infection with Legionella

A

Most people will feel ill, but then clear the infection

Tip of the iceberg:
• immunocompromised will get full blown disease

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12
Q

Describe what happened at the Melbourne Aquarium

A

2000
Just before the Aquarium opened
Legionella in the air conditioning
SPread to many people working around the site

Since then, tight regulations on cooling towers etc.

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13
Q

What are the different places where Legionella can be picked up?

A

Community acquired
• eg Melbourne Aquarium

Nosocomial

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14
Q

How is Legionella transmitted?

A 
Aerosols
Man made water sources
•  cooling towers
•  spas
•  fountains
•  car wash
•  showers

Cannot be transferred from person to person

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15
Q

What are the risk factors for Legionnaire’s disease?

A 
•  Immune deficiency
•  Drinking
•  Male gender 
•  Old age
•  Co-morbidity: 
- smoking
- poor lung function
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16
Q

Why is Legionella called an accidental pathogen?

A

Infection in a human is a dead end for the pathogen

It can not be spread further from there

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17
Q

Why does Legionella grow in man made water sources?

A

Higher than normal temperature

Favourable conditions for the bacteria

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18
Q

What are some important Legionella outbreaks?

A

Philadelphia 1976
• American Legion convention

Netherlands, 1999
• Whirlpool spa

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19
Q

How are water sources tested?

A

Water sample taken
Growth on medium
Viable count test

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20
Q

How did they identify Legionella initially?

A

Philadelphia outbreak
Initially, didn’t know what is was
Took a biopsy
Growth in pig cells

21
Q

How is Legionella pneumophila cultured?

A 
Charcoal agar (iron and cysteine)
•  because it is very fastidious

Dessicated white colonies

22
Q

How is Legionella treated?

A

Antibiotics - Erythromycin
Macrolides
Auinolones

23
Q

How is Legionella detected in the lab?

Describe the features of this test

A 
Urine antigen test
•  very high specificity
•  rapid
•  non-invasive
•  only serogroup 1
24
Q

What is seen in the urine in people with Legionella infection?

A

LPS in the urine

25
Q

What does high specificity of a test mean?

A

Very few false positives

26
Q

Describe the pathogenesis of Legionella

A
  1. Taken into lung
  2. Taken up by alveolar macrophages
  3. Avoids phagolysosome fusion
  4. Recruits host cell vesicles
  5. Recruits rough ER into the vaculole
  6. Grows and replicates in alveolar macrophages
  7. Macrophage dies
  8. Released to infect more macrophages
27
Q

Describe the appearance of the alveolar macrophage after infection with Legionella

A

Very large vacuole forms

Full of Legionella bacteria

28
Q

How does Legionella survive in the environment?

A

Not free living
Must infect amoebae
• survives and resplicates in amoebae
• kills amoebae and spreads further

29
Q

What are amoebae?

A

Single celled phagocytes

Take up bacteria as a food source

Training ground for pathogens

30
Q

Describe the role of amoebae in transmission of Legionella

A
  • Amoebae in cooling towers

* Amoebae protect the bacteria from disinfectants and biocides

31
Q

What is the difference between Legionella and other intracellular bacteria pathogens?

A

Legionella not at all evolved to survive in human cells

32
Q

Describe normal phagocytosis

A
  1. Phagosome formed around bacteria
  2. Fusion of lysosomes
  3. Early endosome → lysosome
  4. Degradation of bacteria
    • hydrolytic enzymes
    • ROS
    • RNS
33
Q

How does Legionella avoid killing once phagocytosed?

A
  • prevents lysosomal fusion
  • recruitment of ER exit vesicles
  • vesicles coat the outside of the vacuole
  • vacuole look like ER → obtains ribosomes, allowing replication
34
Q

What are LCVs?

A

Legionella containing vacuoles

  • don’t acidify
  • don’t fuse with lysosomes
  • come to resemble rER
35
Q

What makes the LCV resemble ER?

A

Retains ER markers on the membrane

  1. Type IV secretion system in membranes of bacterium
  2. Interacts with host cell membrane
  3. Transfers proteins into the host cell
36
Q

What is the name of the T IV SS of Legionella?

A

Dot / Icm secretion system
Defective organelle trafficking
Intracellular multiplication

37
Q

Where is Dot/Icm SS found?

A

Poles of bacterium

38
Q

How many different proteins are injected by the type IV SS?

A

300 ‘effector’ proteins

39
Q

What do the effector proteins do?

A
  • similar to eukaryotic proteins
  • mimic eukaryotic function
→ take over eukaryotic cell processes such as:
•  mitochondrial activity
•  gene transcription and translation
•  apoptosis
•  GTPase activity
•  vesicle trafficking
40
Q

Do many bacteria have these ‘eukaryotic proteins’

A

No, almost exclusively Legionella have them

Due to close evolution of Legionella with amoebae

41
Q

Describe how Legionella targets host GTPases

A

Legionella has taken up a Sec7 domain from a eukaryotic cell

Sec7 domain in the RalF
RalF is a Guanine exchange factor

  1. RalF recruits Arf1 (a GTPase) to the LCV
  2. RalF activates Arf1
  3. Arf1 controls vesicle fusion
42
Q

What is the function of GTPases?

A

Regulate many processes in cells
• vesicle trafficking, for example

  1. GEF swaps GDP → GTP
  2. GTPase now active
43
Q

What is Arf 1?

A

A GTPase in the host cell

• controls vesicle fusion

44
Q

What is a GEF?

A

Guanine exchange factor

Activates GTPase

45
Q

What is Sec7?

A

A domain in RalF (a GEF in Legionella)

46
Q

Describe the immune response to Legionella

A
  • inflammatory cytokine response
  • neutrophils
  • NK
  • T and B cells response
47
Q

Which cytokines are required for an effective immune response?

A

TNF, IL-12, IFN-gamma

48
Q

What is required for clearance of Legionella?

A

T and B cell responses

MIIM20002 - Microbes, Infections, Responses (32 decks)

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