- Gram-negative aerobe, cause of legionellosis or Legionnaires’ disease.
- Common environmental organisms 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).
- Commonly infect free-living amoeba and other ciliated protozoa as natural hosts for this bacteria.
- 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 a pneumonia epidemic at the American Legion Convention in Philadelphia in 1976.
- Others: less frequent, occasional causes of legionellosis
- L. pneumophila serogroups 2-15
- L. micdadei
- Sometimes referred to as the "Pittsburgh pneumonia agent."
- Alternatively, the organism has been called Tatlockia micdadei
- L. dumoffi
- L. longbeachae
- L. bozemanii
- Legionella do not grow on the most commonly used microbiologic media; buffered charcoal yeast extract (BCYE) agar [Fig 1] is preferred.
- Legionella are poorly visualized with Gram stain but may be seen as a Gram negative [Fig 2]. Silver stains such as Warthin-Starry or Dieterle stains [Fig 3] are preferred.
- It may weakly stain acid-fast but loses this characteristic when grown in culture.
- An intracellular pathogen, effective drugs in animal models include fluoroquinolones, macrolides, TMP/SMX, rifampin and doxycycline.
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