Atypical Pneumonia - Legionella and Mycoplasma

Question 1

What type of pathogen is Legionella?

Answer 1

Opportunistic facultative intracellular pathogen (live with or without oxygen)

Question 2

By what means do patients acquire Legionella?

Answer 2

Aspiration/inhalation of contaminated water - NOT PERSON TO PERSON

Question 3

Describe the cellular pathogenesis of the Legionella. What is the natural lifecycle for Legionella? What is the dead-end host for Legionella?

Answer 3

Legionella survive monocyte/macrophage endocytosis and alter endosomes so that they can multiply and escape; Natural lifecycle: Betwixt amoebas; Humans are dead-end hosts

Question 4

What caused the increase in Legionella infection?

Answer 4

Increased use of cooling towers and whirpools spas

Question 5

What can Legionella outbreaks be traced back to?

Answer 5

Contaminated locations NOT PEOPLE

Question 6

What is the optimal Dx for Legionella infection?

Answer 6

BOTH urine test and culture of respiratory secretions

Question 7

What is important for Legionella growth?

Answer 7

Special fastidious media

Question 8

What are the three steps in Dx geriatric community-acquired pneumonias?

Answer 8

1. Take samples for culture/ELISA
2. Start Tx with levofloxacin
3. Get labs back

Question 9

What is a colloquial name for pneumonia caused by Mycoplasma?

Answer 9

“Walking pneumonia”

Question 10

What function of the respiratory tract does the Mycoplasma exotoxin target?

Answer 10

The mucociliary escalator causing ciliostasis

Question 11

What allows M. pneumoniae to dodge AB treatment?

Answer 11

Slow growth and ability to hide within cells

Question 12

What are the typical Tx for M. pneumoniae?

Answer 12

Tetracyclines or macrolides

Question 13

How are phagosomes altered by Legionella?

Answer 13

They alter the phagosomes so that they don’t merge with a lysosome

Question 14

What are the virulence factors of Legionella?

Answer 14

1. Dot/Icm locus: Type IV secretion system alters endosome
2. pilE & pilD - Type IV pili for attachment
3. Pep/pro: Metalloproteinase for endosome escape

Question 15

What are the three possible outcomes of infection with Legionella?

Answer 15

1. Asymptomatic seroconversion
2. Pontiac Fever
3. Legionnaires Disease

Question 16

What would be the stereotypical patient with all the risk factors for contracting Legionnaires disease?

Answer 16

A 65 yo male immunosuppressed smoker with a chronic swallowing disorder and heart disease at a convention

Question 17

What are the two major methods for Dx Legionella infection? Problems with each method?

Answer 17

• Rapid urine antigen test - Only detects LP1 strain of Legionella (90% US patients)
• Culture - Difficult to grow, takes time,

Question 18

What is the best Tx for Legionella infection? Why?

Answer 18

Fluoroquinolones Levofloxacin and Trovafloxacin because they penetrate cells and also cover for M. pneumoniae and S. pneumoniae

Question 19

A young adult patient presents with nonproductive cough, sore throat, and all around mild cold like Syx that has persisted. A sputum culture is shown below. What is your Dx? What is unique about the structure of these organisms? How are they describe on microscopy?

Answer 19

• Mycoplasma pneumoniae
• No cell wall, cholesterol in cell membrane
• “Fried Eggs”

Question 20

How is M. pneumoniae transmitted?

Answer 20

Aerosols

Question 21

What are the virulence factors of M. pneumoniae?

Answer 21

• P1 adhesin: Adheres to sialic acid residues on epithelial surfaces
• CARDS exotoxin: Causes ciliostasis

Question 22

What is the general course and Tx of M. pneumoniae?

Answer 22

Generally self-resolving but can be treated with Fluoroquinolones, Erythromycin, Azithromycin, Clarithromycin, Tetracycline