13. Legionella & TB Flashcards
What bacterium causes Legionnaire’s disease?
Legionella pneumophila
How does Legionella pneumophila cause Legionnaire’s disease?
Evasion of destruction by phagosome
Legionella only grow?
Intracellularly in macrophages - do not grow on agar plates
A non-pneumonic variant caused by the same species as Legionella pneumophila is called?
Pontiac fever
Non-pneumonic - found other places besides the lungs
Features of Legionella species?
- Poorly staining
- Obligate (needs cells to replicate in)
- Aerobic
- Gram negative bacilli
- Tricky to culture, visualise & stain
- Rod-shaped
Is L. pneumophila spore-forming?
No
Symptoms of Legionnaire’s disease?
Initial symptoms within 2-10 days may include loss of energy, headache, nausea, aching muscles, high fever & chest pains.
Victims who survive may suffer permanent physical or mental impairment (20% fatality rate)
Has person-person spread of Legionnaire’s disease ever been demonstrated?
No
Death rate of those identified with Legionnaire’s?
20%
10,000 - 100,000 cases in US
How is Legionnaire’s contracted?
By inhaling airborne water droplets containing Legionellae
Legionnaire’s disease is particularly associated with?
Man made things e.g cooling water used in air conditioning
Where does infection by Legionella begin in the body?
Lower respiratory tract
Legionnaire’s disease pathogenesis:
- Bacteria bind alveolar macrophages via complement receptors & are engulfed into a phagosomal vacuole
- T4SS stimulates the uptake of bacteria into the macrophage
- Bacteria block fusion of lysosomes with phagosome, preventing normal acidification of phagolysosome
- Bacilli multiply within phagosome (which becomes a Legionella-containing vesicle)
- Phagosome modified to become a privileged niche for bacteria to replicate
- Eventually, the cell is destroyed, releasing a new generation of microbes to infect other cells
Why is infection by Legionella difficult to diagnose?
Because they only grow inside macrophages
What happens if phagocytosis is prevented by treatment with cytochalasin?
The bacteria (Legionella) are denied access to the intracellular environment and growth does not occur
True or False: Legionella do not replicate in water but can infect amoeba and multiply
True
Amoeba are a training ground for intracellular bacteria.
What are the most important virulence factors in Legionella?
Those that help modify the phagosome
What does Legionella use to secrete proteins into the phagosome itself?
Type 4 Secretion System
What is the most important virulence factor in Legionella pnuemophila?
Dot/Icm T4SS
Dot = defect in organelle trafficking, Icm = intracellular multiplication
What gene has been shown to have some role in adhesion, invasion and phagosome trafficking in macrophages and amoeba?
RtxA gene
What has pore-forming activity and is required for bacterial egress from mammalian or protozoan cells after bacterial replication is complete?
IcmT
Different strains of Legionella have different…
effector profiles
The symptoms of Legionella infection undoubtedly result from a combination of what?
- Physical interference with oxygenation of blood
- Ventilation-perfusion imbalance in the remaining lung tissue, and
- Release of toxic products from bacteria & inflammatory cells
What greatly reduces the death rate of Legionnaire’s?
Prompt treatment with erythromycin
