History and Legionella

Question 1

What is Koch’s Postulate?

Answer 1

1. The organism is found in the diseased
   tissue.
2. The organism can be isolated in pure culture.
3. Inoculation of animals with organisms from the pure culture produces a similar disease.
4. The organism can be recovered from the lesions of these animals.

Question 2

How is Legionella pneumophila transmitted?

Answer 2

They grow in amoebae in the water. When misted (aerosols) they reach the lungs and cause pneumonia. Legionella are thermophiles, and there is no person-to-person transmission.

Question 3

What are the risk factors of legionella?

Answer 3

older than 50, immunosuppressed, diabetes, cancer, COPD, smoker

Question 4

What is Pontiac Fever?

Answer 4

Caused by the serogroups 1-6 of L. pneumophila. Only recognized in outbreaks. It is a self-limiting, flu-like illness with NO PNEUMONIA and is not fatal.

Question 5

How can you diagnose L. pneumophila?

Answer 5

1. Isolation on buffered charcoal yeast extract agar
2. Detection of Legionella antigens in urine for serogroup 1 ONLY.
3. Visualization of organisms in smears by fluorescent antibody
4. Retrospectively, by a 4-fold rise in indirect fluorescent antibody titer against the organism, comparing acute versus convalescent serum samples. (retrospective)
5. Molecular probes

Question 6

How do you treat L. pneumophila?

Answer 6

1. Erythromycin (able to penetrate into mammalian cells, and L pnemophila lives in macrophages)
2. DO NOT use ampicillin (not able to penetrate the cells)

Question 7

Where does L. pneumophila live and grow?

Answer 7

Lives inside amoebae, then ingested by macrophages by coiling phagocytosis and then has intracellular replication