Legionella

Question 1

Legionella morpholgy:

Most common ?

Answer 1

Gram-negative (poorly staining) coccobacilli
Motile

L.pneumophila

Question 2

Just read

Most infections due to serotype

Answer 2

1- L.pneumophila

2- second most common L.longbeachae

Question 3

Culture of L.pneumophila

Medium used to culture L.pneumophila :

Answer 3

.Bufferd charcoal yeast extract (BCYE) ager
.Incubation in 3-5% co2 atmosphere for 3-4 days at 37°c
.Gray-white to blue-green, glistening, convex, circular colonies with a cut-glass type internal granular speckling by plate microscopy
.Blue-white autofluorescences on long wave UV light

Question 4

Specific identification of L.pneumophila colony :

Answer 4

By staining of culture with fluorecent-labelled monoclonal antibody

Question 5

L.pneumophila habitat and transmission to humans :

Answer 5

Aquatic bacterium in biofilm, single or living inside water amoeba
Multiplies inside amoeba and kills the host
Present in air-conditioning ducts and cooling towers as biofilms

Transmission to humans by respiratory rout by aerosol (liquid droplet) inhlation
* there is no human to human transmission

Question 6

Examble of intracellular pathogen :

Answer 6

Growth of L.pneumophila in water amoeba or macrophage on the human lung
Mycobacterium tuberculosis

**E.coli is not an intracellular pathogen

Question 7

Internalisation of legionella by ?

Answer 7

Coiling phagocytosis by amoeba and macrophage

Question 8

Pathogenesis of L.pneumophila :

Answer 8

Entery to the body :
Entery to respiratory tract by aspiration of water containing the organism or inhalation of contaminated aerosol.
Entery in the cell :
Organism phagocytosed by alveolar macrophage
Phagosome (vacuole carrying the bacteria) fails to fuse with lysosome
Multiplcation of the organism
Rupture of cell with release of new crop of bacteria

Question 9

Virulence factors of L.pneumophila :

Answer 9

1- Mip : macrophage infectivity promoter, required for infection of phagocytic cells, protozoa
2- Dot/icm: defective for organell traffiking/intraellular mutipilication ( diverts phagosome from endocytic pathway)
Type IV secretory system (syring-like) for secretion of virulence factors required in phagocytic cells and protozoa.
3- pmi: protozosn and macrophage infectivity
4-mak : macrophage killing
5- mil: macrophage-specific infectivity locus

Question 10

Spectrum of disease (L.pneumophila)

Answer 10

Asymptomatic to life-threating disease (pneumonia, Legionnaire’s disease) patchy unipolar infiltrate to consolidation on radiology

Systemic involvment may include : diarrhea
Kidney and liver dysfunction

Ponatic fever ( milder form of legionnair’s disease) : flu-like illness, lungs not affected

Other infections-wound abscess, enecephalitis, endocarditis! Cellulitis , peritonitis

Question 11

Individuals at risk of L.pnemophila infection

Answer 11

immunocompromised patients 
    Person older than 50
    Smokers, alcholics, patients with      malignanct 
     Organ transplant patients 
     Patients on corticosteroides

Question 12

Specimens for diagnosis L.pnumophila :

Answer 12

Difficult to get sputum in early disease (few patients have productive cough)

Gram staining of sputum will not reveal the organism (take up the stain poorly)

Urine (antigen detection by ELISA especially serogroup 1, most commenly used test)

Question 13

Molecular tests
Serodiagnosis
L.pneumophila

Answer 13

Molecular test :
PCR tests targeting 5S rRNA, 16S rRNA, mip gend on respiratory specimens, serum and urine.
More sensitive than other tests

Serodiagnosis (serum antibodies):

Question 14

You can treat this disease with antibiotics.

L.penumophila

Answer 14

Antimicrobial therapy :
Macrolides: erythromycin, azitharomycin
Fluroquinolone: ciprofloxcin, levofloxacin
Tertacycline

Question 15

How to control Legionella :

Answer 15

Chlorine as a bioacid not effective in killing Legionella

But : monochlorine , UV light treatment or superheating of water to 60°c

Question 16

Immunity to Legionella :

Answer 16

Antibodies not protective
Cell-mediated immunity protective (cytokines produced by infected macriphages activate polymorphs and natural killer cells which eliminate the bacteria)