Legionella

Question 1

Morphology (2)

Answer 1

Gram Negative coccobacilli

Motile

Question 2

Diseases (3)

Answer 2

Atypical pneumonia

Community-acquired pneumonia

Nosocomial pneumonia

Question 3

Species (2)

Answer 3

L.pneumophila (most common)

L.longbeachae

Question 4

Gram stain Appearance

Answer 4

POORLY staining, THIN gram-negative coccobacilli

Question 5

Culture (5)

Answer 5

Buffered Charcoal Yeast Extract (BCYE) agar

Incubation 3-5% CO2 for 3-4 days at 37 degrees

BLUE-GREEN, glistening, convex, circular colonies with CUT-GLASS type internal granular speckling by plate microscopy

Blue-white AUTOFLUORESCENCE on long wave UV light (Fluorescent Labeled Monoclonal Antibody)

STICKY appearance of colony

Question 6

Habitat (4)

Answer 6

Aquatic bacterium in biofilm, single or living inside water amoeba

Multiplies inside amoeba and kills host

Also present in air-conditioning ducts and cooling towers as biofilms

HEAT-RESISTANT and CHLORINE-RESISTANT

Question 7

Transmission (2)

Answer 7

To humans by RESPIRATORY route by aerosol (liquid-droplet) inhalation

NO HUMAN-HUMAN transmission

Question 8

Intracellular Pathogen (2)

Answer 8

In water amoeba

In macrophage in human lung

Question 9

How is Legionella internalized?

Answer 9

By coiling phagocytosis of Ameoba and Macrophage

Question 10

Pathogenesis (5)

Answer 10

1- Entry into respiratory tract by aspiration of water containing organism or by inhalation of contaminated aerosol

2- Organism phagocytosed by alveolar macrophage

3- Phagosome fails to fuse with lysosome (NO ACIDIFICATION)

4- Multiplication of organism in protected environment of phagosome

5- Rupture of cell with release of new crop of bacteria

(RER allows pathogen to obtain nutrients from host)

Question 11

Virulence Factors (5)

Answer 11

Mip—> (Macrophage infectivity promoter) —> Required for infection of Phagocytic cells, Protozoa

Dot/Icm —> (Defective for organelle trafficking) / (Intracellular multiplication) —> Diverts phagosome from Endocytic pathway; Type IV secretory system (syringe-like) for secretion of virulence factors required in Phagocytic cells and Protozoa

Pmi —> Protozoan and macrophage infectivity

Mak —> Macrophage killing

Mil—> Macrophage-specific infectivity locus

Question 12

Entry in Ameoba / Macrophage

Answer 12

Ameoba —> Receptor-mediated uptake, Requires dot/icm, Gal/GalNac receptor

Macrophage —> Actin dependent, Requires dot/icm

Question 13

Release from Ameoba / Macrophages

Answer 13

Ameoba —>Necrosis (pore formation)

Macrophages —> Necrosis (pore formation), Apoptosis

Question 14

Radiology

Answer 14

Patchy UNILOBAR infiltrates

Question 15

Systemic Involvement (3)

Answer 15

Diarrhea

Kidney dysfunction

Liver dysfunction

Question 16

Other infections (5)

Answer 16

Wound abscess

Encephalitis

Endocarditis

Cellulitis

Peritonitis

Question 17

Pontiac Fever (2)

Answer 17

Flu-like illness

Lungs NOT affected

Question 18

Diagnosis (3)

Answer 18

MOST COMMON —> URINE (antigen detection by ELISA especially serogroup 1)

Respiratory secretions (BAL) —> Fluorescent antibody tests

NOT GRAM STAIN!!!!

Question 19

Serodiagnosis (serum antibodies)

Answer 19

Acute and Convalescent (recovered) sera taken 2 weeks apart:

• Demonstration of FOUR-FOLD RISE in Legionella antibody-titre by INDIRECT FLUORESCENT ANTIBODY TEST
• Single serum sample with titre of 256 or more with clinical characteristic is diagnostic

Question 20

Antimicrobial Therapy (3)

Answer 20

1- Macrolides (Erythromycin, Azithromycin)

2- Flouroquinlone (Ciprofloxacin, Levofloxacin)

3- Tetracycline

Question 21

Control (3)

Answer 21

Monochloramine (CHLORINE = NOT EFFECTIVE)

UV Light treatment

Superheating water to 60 degrees