Legionella pneumophila Flashcards
General Feature and habitat of Legionella pneumophila
Gram – (but stain poorly, therefore needs silver stain)
Coccobacillus
Habitat- moist, watery places; rivers, streams, air-conditioning water cooling tanks
Biochemical Properties of Legionella pneumophila
Oxidase +
Catalase +
Facultative intracellular- can enter PMNs (in nature inside amoebae)
Pathogenesis of Legionella pneumophila
Transmitted by aerosols- from contaminated air conditioning, showers, baths, humidifiers, aquarium, gardens hoes and fountains (no human-to-human)
Spreading is travel associated (i.e. hotels), nosocomial and community acquired
Higher risk for immunosuppressed patients (e.g. renal transplant patients)
Legionella multiply inside cells (e.g. macrophages) until numerous, then lyse the cell
Virulence factors- proteases (for invasion), phospholipases (for cell lysis)
Clinical Features Legionellosis
Pontiac fever- fever, malaise, headache, chills; self-limiting (without pneumonia)
Legionnaires’ disease: (Pneumonia form, more common in smokers > 55 years old)
Atypical pneumonia- X-ray show patchy infiltrate of one lobe, rapidly progress
Unproductive coughing, which can later be bloody
Hyponatremia (low Na+ levels) and liver enzymes in laboratory diagnosis
Headache and neurological symptoms / confusion (30%)
Diarrhea and vomiting (but legionella is not found in GI tract)
High fever
Diagnosis of Legionella pneumophila
Buffered Charcoal-Yeast Extract agar (BCYE) from respiratory sample - Growth requires iron and cysteine (fastidious)
Urine antigen test- rapid diagnosis by immune chromatography from urine sample
Serology: (can use serum, urine or BAL- broncho-alveolar lavage)
Antigen detection- DIF (BAL sample), ELISA (serum sample) or IC
Antibody detection- IF or ELISA (not too accurate since IgG persist high for long time)
PCR, hybridization
Treatment of Legionella pneumophila
Fluoroquinolone (empirically- start with this)
Macrolide
Rifampin can also be used or combination of all
