Legionella species


Atypical Organisms
>Chlamydophila pneumoniae
>Chlamydophila psittaci
>Coxiella burnetii
>Legionella species ( L. pneumophila) led
>Mycoplasma pneumonia

Legionella species

  • pathogenic group of gram negative bacterium. 
  • Common in many environments, including soil and aquatic systems, with at least 50 species identified.  
  • Requires the presence of cysteine and iron to grow and therefore does not grow on common blood agar media used for laboratory based total viable counts or on site dipslides.   
  • Many hospitals use the Legionella Urinary Antigen test for initial detection when Legionella pneumonia is suspected (results can be obtained in a matter of hours rather than the five days required for culture).   
  • L. pneumophila, causes Legionnaires Disease. L.longbeachae causes Pontiac Fever.


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Legionella pneumophila:  

  • Thin, aerobic, pleomorphic, flagellated, non-spore forming, Gram-negative bacterium of the genus Legionella.
  • L. pneumophila is the primary human pathogenic bacterium in this group and is the causative agent of legionellosis or Legionnaires’ disease.
  • L. pneumophila is a gram-negative, non-encapsulated, aerobic bacillus with a single, polar flagellum often characterized as being a coccobacillus. It is aerobic and unable to hydrolyse gelatin or produce urease. It is also non-fermentative.
  • It is oxidase- and catalase-positive, and produces beta-lactamase.
  • L. pneumophila has a colony morphology that is gray-white with a textured, cut-glass appearance; it also requires cysteine and iron to thrive.
  • Legionella stains poorly with gram stain (due to its unique lipopolysaccharide-content), stains positive with silver, and is cultured on charcoal yeast extract with iron and cysteine.
  • Source: https://en.wikipedia.org/wiki/Legionella_pneumophila

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Important considerations:  The choice of an agent should be based on local antimicrobial sensitivities, site of infection, cost, and comorbid conditions.   Generally, the most common agents/regimens are listed first.  Total duriation of therapy is usually 7 to 10 days, however, for more severe cases or for immunosuppressed patients consider prolonging therapy for up to 3 weeks.

  1. Levofloxacin 750 mg IV/PO once daily
  2. Moxifloxacin 400mg orally/IV once daily
  3. Azithromycin 500mg oral/IV once daily.  Some references suggest giving 1 gram x 1  for 1st dose, then continue with 500mg daily.
  4. Doxycycline 100mg oral or IV twice daily
  5. Bactrim 8 to 10 mg/kg/day (based on trimethoprim component) IV divided in 2-4 doses.

Note: In severe disease consider adding Rifampin 300-450 mg  orally/IV q12h PLUS one antibiotic from above.


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