Legionella

Question 1

Legionella pneumophila

Morphology

Culture

Answer 1

Gram negative long rod 2-5 uM long bacilli

Pleomorphic, flagellated at one pole

non-spore-forming

Aerobic (pneumophila)

Catalse positive, Oxidase positive

Hydrolyzes hippurate

Culture:

Fastidious, requires L-cysteine and Iron salts

BCYE: Buffered Charcoal Yeast Extract agar with alpha-ketoglutarate and pH 6.9. at 35C and 90% humidity

Long incubation, 3 days. >2 weeks in blood cultures

Pleiomorphic colonies: round or flat, colorless to irridescent pink or blue. Transparent or speckled

Colonies glow white/blue when grown on BCYE agar under UV light.

Question 2

Legionella pneumophila

Habitat

Transmission

Answer 2

Ubiquitous in moist areas - A/C units, fountains, cooling systems for machines, shower heads, dirty sinks

Transmission: infects immunocompromised patients by inhalation of aerosolized bacteria.

Can be a nosocomial infection, sporadic infection, or an epidemic infection (ex. a fountain or building A/C unit is infected and contaminates everyone there).

No human-to-human transmission (bacteria is intracellular, and not in respiratory droplets)

Question 3

Legionella pneumophila

Clinical disease

Answer 3

Disease:

Initial “Pontiac fever”: 2-3 days of incubation and a fever with headache, joint, and muscle pain develops and then resolves within a few days.

In immunocompromised or weak patients, Legionaires disease then develops.

Acute purulent alveiolar pneumonia

Very high fever

Initial non-productive cough

Later, sputum producing and may be bloody

Intra-alveolar accumulation of macrophages, PMC leukocytes, RBCs, and proteinacious exudate.

Little or no inflammation in brochioles and upper airways

Legionella bacteria is inside of the phagocytes.

Headache, muscle pain, and GI symptoms occur as well.

Question 4

Legionella pneumophila

Virulence factors

Answer 4

Proteases and Phospholipases: allow them to escape macrophage endosomes after they replicate inside of the macrophages.

Question 5

Legionella pneumophila

Diagnosis

Treatment

Answer 5

Clinical specimen and growth on BCYE medium. at 5% CO₂

Silver impregnation staining the direct smear or direct-IF staining, showing Pleiomorphic cells.

Serology:

Indirect Immunostain using patients sera as the primary antibody

Treatment:

Macrolides: azithromycin, clarithromycin

Respiratory Fluroquinolones (topisomerase inhibiting bactericidal)