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- Gram-negative aerobe, cause of legionellosis or Legionnaires’ disease.
- Common environmental organism, found in warm water sources (e.g., 32°- 45°C temperature range as in warm ponds, air chillers, industrial air conditioning systems, water systems include storage and hot water).
- Legionella spp. include >60 species and 70 serotypes.
- Most are capable of causing human disease.
- L. pneumophila serogroup 1: most common, accounting for 80-90% of cases of Legionnaires’ disease.
- The appellation is based on the first recognition of the disease in an epidemic of pneumonia at the American Legion Convention in Philadelphia in 1976
- Others: L. pneumophila serogroups 2-15, L. micdadei, L. dumoffi, L. longbeachae, and L. bozemanii cause disease less often.
- Legionella do not grow on most commonly used microbiologic media; buffered charcoal yeast extract (BCYE) agar is preferred.
- Legionella are poorly visualized with Gram stain. Silver stains such as Warthin-Starry or Dieterle stains are preferred.
- An intracellular pathogen, effective drugs in animal models include fluoroquinolones, macrolides, TMP/SMX, rifampinand doxycycline.