What is the role of gram stains and cultures in the diagnosis of Legionella infection?

Updated: Nov 13, 2018
  • Author: Mobeen H Rathore, MD, CPE, FAAP, FIDSA; Chief Editor: Russell W Steele, MD  more...
  • Print

Gram stains and cultures of sputum, lower respiratory tract secretions, tissue, or blood

  • In children, the best samples are obtained by bronchoscopy. [16] Samples obtained by bronchoalveolar lavage (BAL) are better than those from bronchial washings. In addition, fluid or pus from normally sterile sites (eg, cerebrospinal fluid [CSF], pleural fluid, peritoneal fluid) should be cultured.

  • Gram stain may show small, pleomorphic, weakly staining, gram-negative bacilli or no organisms with a large number of polymorphonuclear leukocytes. L micdadei may stain with acid-fast stain.

  • Culturing, considered the criterion standard, requires the use of special media (buffered charcoal yeast extract [BCYE] agar with L-cysteine and ferric ions to support growth, antibiotics to prevent overgrowth of other organisms, and dyes to impart a distinctive color to the organisms).

  • Specialized techniques may require 2-7 days to isolate Legionella organisms. Routine sputum cultures provide 80% sensitivity and 100% specificity. Culture from BAL specimens has a sensitivity of 90% or greater.

  • Since co-infection with other pathogens often occurs, isolation of other pathogens does not exclude the possibility of concomitant Legionella infection.

  • Legionella species can also be isolated from blood cultures; yield can be optimized by blind subculture (before sample results turn positive) onto BCYE agar from radiometric culture bottles.

Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!