Genus Legionella Flashcards
1
Q
Classification
A
Family: Legionellaceae
Genus: Legionella
40 species
Most important:
- Legionella pneumophila
2
Q
Morphology
A
Gram negative rods (but stains poorly with standard gram staining)
- visualised by silver stain
3
Q
Growth characteristics
A
Aerobic
Fastidious
Oxidase positive
4
Q
Antigenic structure
A
LPS
5
Q
Virulence factor
A
Protease Phosphatase Lipase DNAase RNAase
(DLR train PP)
A major secretory protein, a metalloprotease, has hemolytic and cytotoxic activity; however this protein has not been shown to be a required virulence factor.
6
Q
Disease
A
Most severe:
Legionnaires’ disease (“atypical” pneumonia)
- most common in smokers
- X-ray shows patchy infiltrate with consolidation on one side
- associated with:
> hyponatremia
> neurological symptoms: headache + confusion
> diarrhea
> fever (> 40oC)
Less severe:
Pontiac fever -> self-limited fever and malaise
7
Q
Microbiological diagnosis
A
- microscopy: silver impregnation
- culture: charcoal yeast extract agar containing increased amounts of iron and cysteine
- rapid diagnosis: urinary antigen
- oxidase positive
- serologically diagnosis: detecting rise in antibody titer in patient’s serum
8
Q
Treatment and prevention
A
Treatment:
- macrolides: azithromycin or erythromycin
- fluoroquinolones associated with less complications and equally as effective
Prevention:
No vaccine or prophylactic drug
