5. Legionella Flashcards
Legionella pneumophila are gram()? Non motile or motile? What shape?
Gram negative, motile, coccobacilli
> 60 species in the genus (legionella genus) - 27 species pathogenic to humans - most and 2nd most are?
Most common is L. Pneumophila w/ >15 serotypes
2nd most common is L.longbeachae
What medium is used for L. Pneumophila ?
Buffered charcoal yeast extract (BCYE) agar
Incubation in 3-5% CO2 for 3-4 days at 37C
Culture of L.pneumoniaphila?
- Gray - white to Blue - green w/ cut glass appearance by plate (dissecting) microscope
- Blue- white autofluorescence on long wave of UV light
- BCYE agar
- specific identification of colony by staining of culture w\ fluorescent-labelled monoclonal antibody
Habitat of L. Pneumophila?
- Aquatic bacterium in biofilm, single or living inside water amoeba ( multiplies inside amoeba and kills host)
- in Air-conditioning, colling towers as biofilm
- heat and chlorine resistent
- transfer to humans respiratory by aerosol (liquid droplet) inhalation
- NO HUMAN TO HUMAN TRANSMISSION
Is L.pneuomophila an intracellular pathogen?
Yes , E.coli is not.
Internalisation or legionella by?
Coiling phagocytosis by amoeba and macrophage ( also grows bc of them)
- macrophage in human lung
- amoeba could also be in water
Explain the pathogensis (entry) of L.pneuomophila into human lungs?
- Entry into resp. Tract by aspiration of water containing it or by inhalation of contaminated aerosol
- Organism phagocytosed by alveolar macrophage
- PHAGOSOME FAILS TO FUSE W/ LYSOSOME
- multiplication and rupture of cell releasing more bacteria
what organelle may allows the pathogen to obtain nutrients from the host?
RER: since its function is to synthsize and export proteins
What are the virulence factors of L.pneuomophila?
- MIP: Macrophage infectivity promoter, required of phagocytic cells, protozoa ( water amoeba)
- Dot/Icm: Defective for organelle trafficking/ intracellular multiplication (diverts phagosome from endocytic pathway): TYPE 4 SECRETORY SYSTEM (SYRINGE-LIKE)
- PMI: protozoan & macrophage infectivity
- MAK: macrophage killing
- MIL: macrophage- specific infectivity locus
Entry and Release in amoebae and Macrophage by what? What happens when they do?
Entry: Requires dot/icm
Release: ~ameobea by necrosis - pore formation ~macrophage by APOPTOSIS - necrosis - pore formation
2/ exhaustion of nutrients as the pathogen utilizes it all, leading to AA depletion and ppGpp build up ( leading to intracellular motility)
Spectrum of the disease?
Asymptomatic to life-threatening disease (pneumonia, Legionnaire’s disease); patchy unilobar infiltrates to consolidation on radiology
Pontiac fever (flu-like illness, lungs not affected)
Who are the individuals at risk of L.pneumophila infection?
Immunocompromised patients > 50 yrs Smokers, alcoholics, patients w/ malignancy Organ transplant patients Patients on corticosteroids
Specimens for diagnosis?
- difficult to get sputum in early disease when few patients have productive cough
- resp. Secretions (bronchial alveolar lavage, bronchial aspirate) ideal.
- gram stain of sputum wont reveal the organism
- if sputum obtained, it can be used for fluorescent antibody (serogroup 1)
- urine ( antigen detection by ELISA esp. serogroup 1, most commonly used test)
What are the molecular test used for L.pneumophila?
- PCR tests tarageting 5S rRNA, 16S rRNA, mip gene on resp. Specimens, serum and urine
- more sensitive than other tests
