Legionella

Question 1

What is Legionnaire’s disease?

Answer 1

Acute pneumonia

Caused by >90% of cases caused by Legionella pneumophilla

Question 2

Is Legionella Gram negative or positive?

Answer 2

Gram negative

Question 3

Number of species of Legionella

Answer 3

~50

Question 4

Serogroup of Legionella pneumophilla that causes most cases of Legionnaire’s disease

Answer 4

Serogroup 1

Question 5

To what does serogroup refer?

Answer 5

O antigen

Question 6

Where does Legionella like to live?

Answer 6

Water and soil

Question 7

Can Legionella be spread person-to-person?

Answer 7

No

Only acquired form environment

Question 8

Risk factors in Legionella infection
1)
2)
3)
4)
5)

Answer 8

1) Immunodeficiency
2) Age
3) Smoking
4) Drinking
5) Male gender

Question 9

Environmental sources associated with Legionella infection

Answer 9

Man-made water sources

Cooling towers, spas, fountains, ventilation systems, showers

Question 10

Culturing Leginoella pneumophilla

Answer 10

Charcoal agar

Needs high levels of cysteine and iron

Question 11

Why is charcoal used to culture Legionella?

Answer 11

Charcoal detoxifies toxic metabolites of Legionella

Question 12

Diagnostic test for Legionella infection

Answer 12

Urine antigen test

Question 13

Treatment of Legionella pneumophilla infection

Answer 13

Erythromycin, macrolides, quinolones

Question 14

Pros of Legionella urine antigen test

Answer 14

Non-invasive

90% sensitivity

Question 15

Cons of Legionella urine antigen test

Answer 15

Only detects Legionella pneumophilla serogeoup 1

<76% specificity (false positives can occur)

Question 16

Which human cells do Legionella live and replicate in?

Answer 16

Macrophages

Question 17

How are Legionella so well-adapted to living in human macrophages?

Answer 17

Normally live inside amoebae (eukaryotes)

Amoebae phagocytose, so Legionella can subvert this process in macrophages

Question 18

How do amoebae make eradication of Legionella more difficult?

Answer 18

Amoebae are tough, provide protection against disinfectants and biocides

Question 19

What does Legionella do when it enters a cell?
1)
2)
3)
4)

Answer 19

1) Avoids phagolysosome fusion
2) Interacts with vesicles in secretory pathway
3) ER exit vesicles travelling to the Golgi are attached to vacuole
4) Ribosomes attach to wall of vacuole, feed Legionella proteins

Question 20

Legionella vacuoles
1)
2)
3)

Answer 20

1) Fail to acidify, fuse with lysosome
2) Phagosome does not acquire endosomal markers
3) Phagosome retains ER markers,
resembles rough ER

Question 21

Legionella type IVb secretion system

Answer 21

DOT/Icm

Injects ~300 effector proteins into host cell

Question 22

DOT

Answer 22

Defective interorganelle trafficking

Question 23

Icm

Answer 23

Intracellular multiplication

Question 24

What do injected Legionella effector proteins do?

Answer 24

Mimic eukaryotic protein function

Question 25

How did Legionella acquire eukaryotic-like effector proteins?

Answer 25

Lateral gene transfer from simple protozoans

Question 26

RalF

Answer 26

First identified Legionella effector protein
Guanine exchange factor
Contains Sec7 domain

Question 27

What does RalF do?

Answer 27

Recruits host cell Arf1 GTPase to vacuole

Arf1 controls vesicle fusion

Question 28

How does the immune system clear Legionella?

Answer 28

Most importantly a robust inflammatory response
Neutrophils, NK
T- and B-cells needed for clearance

Question 29

Cytokines important in Legionella clearance

Answer 29

IL-12
TNF
IFN gamma

Question 30

Evidence that T and B cells aren’t very important in Legionella clearance

Answer 30

HIV patients aren’t more susceptible to Legionella infection than healthy people

Question 31

Evidence that the inflammatory response is very important in clearing Legionella

Answer 31

Patients receiving treatment for cancer are more susceptible to Legionella infection